MediaStream Image Capture

Editor’s Draft,

This version:
https://w3c.github.io/mediacapture-image/
Latest published version:
https://www.w3.org/TR/image-capture/
Previous Versions:
Feedback:
public-webrtc@w3.org with subject line “[image-capture] … message topic …” (archives)
Issue Tracking:
GitHub
Editors:
(Google LLC)
Rijubrata Bhaumik (Intel Corporation)
Former Editor:
Giridhar Mandyam (Qualcomm Innovation Center Inc.)
Participate:
Mailing list
GitHub repo (new issue, open issues)
Implementation:
Implementation Status
Can I use Image Capture?

Abstract

This document specifies methods and camera settings to produce photographic image capture. The source of images is, or can be referenced via a MediaStreamTrack.

Status of this document

This is a public copy of the editors’ draft. It is provided for discussion only and may change at any moment. Its publication here does not imply endorsement of its contents by W3C. Don’t cite this document other than as work in progress.

If you wish to make comments regarding this document, please send them to public-webrtc@w3.org (subscribe, archives). When sending e-mail, please put the text “image-capture” in the subject, preferably like this: “[image-capture] …summary of comment…”. All comments are welcome.

This document was produced by the Web Real-Time Communications Working Group.

This document was produced by a group operating under the W3C Patent Policy. W3C maintains a public list of any patent disclosures made in connection with the deliverables of the group; that page also includes instructions for disclosing a patent. An individual who has actual knowledge of a patent which the individual believes contains Essential Claim(s) must disclose the information in accordance with section 6 of the W3C Patent Policy.

This document is governed by the 15 September 2020 W3C Process Document.

1. Introduction

The API defined in this document captures images from a photographic device referenced through a valid MediaStreamTrack [GETUSERMEDIA]. The produced image can be in the form of a Blob (see takePhoto() method) or as a ImageBitmap (see grabFrame()).

Reading capabilities and settings and applying constraints is done in one of two ways depending on whether it impacts the video MediaStreamTrack or not. Photo-specific capabilities and current settings can be retrieved via getPhotoCapabilities()/getPhotoSettings() and configured via takePhoto()'s PhotoSettings argument. Manipulating video-related capabilities, current settings and constraints is done via the MediaStreamTrack extension mechanism.

2. Security and Privacy Considerations

The privacy and security considerations discussed in [GETUSERMEDIA] apply to this extension specification.

Moreover, implementors should take care to prevent additional leakage of privacy-sensitive data from captured images. For instance, embedding the user’s location in the metadata of the digitzed image (e.g. EXIF) might transmit more private data than the user is expecting.

3. Image Capture API

The User Agent must support Promises in order to implement the Image Capture API. Any Promise object is assumed to have a resolver object, with resolve() and reject() methods associated with it.

[Exposed=Window]
interface ImageCapture {
   constructor(MediaStreamTrack videoTrack);
   Promise<Blob>              takePhoto(optional PhotoSettings photoSettings = {});
   Promise<PhotoCapabilities> getPhotoCapabilities();
   Promise<PhotoSettings>     getPhotoSettings();

   Promise<ImageBitmap>       grabFrame();

   readonly attribute MediaStreamTrack track;
};
takePhoto() returns a captured image encoded in the form of a Blob, whereas grabFrame() returns a snapshot of the track video feed in the form of a non-encoded ImageBitmap.

3.1. Attributes

track, of type MediaStreamTrack, readonly
The MediaStreamTrack passed into the constructor.

3.2. Methods

ImageCapture(MediaStreamTrack videoTrack)
Parameter Type Nullable Optional Description
videoTrack MediaStreamTrack The MediaStreamTrack to be used as source of data. This will be the value of the track attribute. The MediaStreamTrack passed to the constructor MUST have its kind attribute set to "video" otherwise a DOMException of type NotSupportedError will be thrown.
takePhoto(optional PhotoSettings photoSettings)
takePhoto() produces the result of a single photographic exposure using the video capture device sourcing the track and including any PhotoSettings configured, returning an encoded image in the form of a Blob if successful. When this method is invoked, the user agent MUST run the following steps:
  1. If the readyState of track provided in the constructor is not live, return a promise rejected with a new DOMException whose name is InvalidStateError, and abort these steps.
  2. Let p be a new promise.
  3. Run the following steps in parallel:
    1. Gather data from the track underlying source with the defined photoSettings and into a Blob containing a single still image. The method of doing this will depend on the underlying device.
      Devices MAY temporarily stop streaming data, reconfigure themselves with the appropriate photo settings, take the photo, and then resume streaming. In this case, the stopping and restarting of streaming SHOULD cause onmute and onunmute events to fire on the track in question.
    2. If the operation cannot be completed for any reason (for example, upon invocation of multiple takePhoto() method calls in rapid succession), then reject p with a new DOMException whose name is UnknownError, and abort these steps.
    3. Resolve p with the Blob object.
  4. Return p.
Parameter Type Nullable Optional Description
settings PhotoSettings The PhotoSettings dictionary to be applied.
getPhotoCapabilities()
getPhotoCapabilities() is used to retrieve the ranges of available configuration options, if any. When this method is invoked, the user agent MUST run the following steps:
  1. If the readyState of track provided in the constructor is not live, return a promise rejected with a new DOMException whose name is InvalidStateError, and abort these steps.
  2. Let p be a new promise.
  3. Run the following steps in parallel:
    1. Gather data from track into a PhotoCapabilities dictionary containing the available capabilities of the device, including ranges where appropriate. The method of doing this will depend on the underlying device.
    2. If the data cannot be gathered for any reason (for example, the MediaStreamTrack being ended asynchronously), then reject p with a new DOMException whose name is OperationError, and abort these steps.
    3. Resolve p with the PhotoCapabilities dictionary.
  4. Return p.
getPhotoSettings()
getPhotoSettings() is used to retrieve the current configuration settings values, if any. When this method is invoked, the user agent MUST run the following steps:
  1. If the readyState of track provided in the constructor is not live, return a promise rejected with a new DOMException whose name is InvalidStateError, and abort these steps.
  2. Let p be a new promise.
  3. Run the following steps in parallel:
    1. Gather data from track into a PhotoSettings dictionary containing the current conditions in which the device is found. The method of doing this will depend on the underlying device.
    2. If the data cannot be gathered for any reason (for example, the MediaStreamTrack being ended asynchronously), then reject p with a new DOMException whose name is OperationError, and abort these steps.
    3. Resolve p with the PhotoSettings dictionary.
  4. Return p.
grabFrame()
grabFrame() takes a snapshot of the live video being held in track, returning an ImageBitmap if successful. grabFrame() returns data only once upon being invoked. When this method is invoked, the user agent MUST run the following steps:
  1. If the readyState of track provided in the constructor is not live, return a promise rejected with a new DOMException whose name is InvalidStateError, and abort these steps.
  2. Let p be a new promise.
  3. Run the following steps in parallel:
    1. Gather data from track into an ImageBitmap object. The width and height of the ImageBitmap object are derived from the constraints of track.
    2. If the operation cannot be completed for any reason (for example, upon invocation of multiple grabFrame()/takePhoto() method calls in rapid succession), then reject p with a new DOMException whose name is UnknownError, and abort these steps.
    3. Resolve p with the ImageBitmap object.
  4. Return p.

4. PhotoCapabilities

dictionary PhotoCapabilities {
  RedEyeReduction         redEyeReduction;
  MediaSettingsRange      imageHeight;
  MediaSettingsRange      imageWidth;
  sequence<FillLightMode> fillLightMode;
};

4.1. Members

redEyeReduction, of type RedEyeReduction
The red eye reduction capacity of the source.
imageHeight, of type MediaSettingsRange
This reflects the image height range supported by the UA.
imageWidth, of type MediaSettingsRange
This reflects the image width range supported by the UA.
fillLightMode, of type sequence<FillLightMode>
This reflects the supported fill light mode (flash) settings, if any.
The supported resolutions are presented as segregated imageWidth and imageHeight ranges to prevent increasing the fingerprinting surface and to allow the UA to make a best-effort decision with regards to actual hardware configuration.

5. PhotoSettings

dictionary PhotoSettings {
  FillLightMode   fillLightMode;
  double          imageHeight;
  double          imageWidth;
  boolean         redEyeReduction;
};

5.1. Members

redEyeReduction, of type boolean
This reflects whether camera red eye reduction is desired
imageWidth, of type double
This reflects the desired image height. The UA MUST select the closest height value this setting if it supports a discrete set of height options.
imageHeight, of type double
This reflects the desired image width. The UA MUST select the closest width value this setting if it supports a discrete set of width options.
fillLightMode, of type FillLightMode
This reflects the desired fill light mode (flash) setting.

6. MediaSettingsRange

dictionary MediaSettingsRange {
    double max;
    double min;
    double step;
};

6.1. Members

max, of type double
The maximum value of this setting
min, of type double
The minimum value of this setting
step, of type double
The minimum difference between consecutive values of this setting.

7. RedEyeReduction

enum RedEyeReduction {
  "never",
  "always",
  "controllable"
};

7.1. Values

never
Red eye reduction is not available in the device.
always
Red eye reduction is available in the device and it is always configured to true.
controllable
Red eye reduction is available in the device and it is controllable by the user via redEyeReduction.

8. FillLightMode

enum FillLightMode {
  "auto",
  "off",
  "flash"
};

8.1. Values

auto
The video device’s fill light will be enabled when required (typically low light conditions). Otherwise it will be off. Note that auto does not guarantee that a flash will fire when takePhoto() is called. Use flash to guarantee firing of the flash for takePhoto() method.
off
The source’s fill light and/or flash will not be used.
flash
This value will always cause the flash to fire for takePhoto() method.

9. Extensions

This Section defines a number of new set of Constrainable Properties for MediaStreamTrack that can be applied in order to make its behavior more suitable for taking pictures. Use of these constraints via MediaStreamTrack's methods getCapabilities(), getSettings(), getConstraints() and applyConstraints() will modify the behavior of the ImageCapture object’s track.

9.1. MediaTrackSupportedConstraints dictionary

MediaTrackSupportedConstraints is extended here with the list of constraints that a User Agent recognizes for controlling the photo capabilities. This dictionary can be retrieved using MediaDevices getSupportedConstraints() method.

partial dictionary MediaTrackSupportedConstraints {
  boolean whiteBalanceMode = true;
  boolean exposureMode = true;
  boolean focusMode = true;
  boolean pointsOfInterest = true;

  boolean exposureCompensation = true;
  boolean exposureTime = true;
  boolean colorTemperature = true;
  boolean iso = true;

  boolean brightness = true;
  boolean contrast = true;
  boolean pan = true;
  boolean saturation = true;
  boolean sharpness = true;
  boolean focusDistance = true;
  boolean tilt = true;
  boolean zoom = true;
  boolean torch = true;
};

9.1.1. Members

whiteBalanceMode, of type boolean, defaulting to true
Whether white balance mode constraining is recognized.
colorTemperature, of type boolean, defaulting to true
Whether color temperature constraining is recognized.
exposureMode, of type boolean, defaulting to true
Whether exposure constraining is recognized.
exposureCompensation, of type boolean, defaulting to true
Whether exposure compensation constraining is recognized.
exposureTime, of type boolean, defaulting to true
Whether exposure time constraining is recognized.
iso, of type boolean, defaulting to true
Whether ISO constraining is recognized.
focusMode, of type boolean, defaulting to true
Whether focus mode constraining is recognized.
pointsOfInterest, of type boolean, defaulting to true
Whether points of interest are supported.
brightness, of type boolean, defaulting to true
Whether brightness constraining is recognized.
contrast, of type boolean, defaulting to true
Whether contrast constraining is recognized.
pan, of type boolean, defaulting to true
Whether pan constraining is recognized.
saturation, of type boolean, defaulting to true
Whether saturation constraining is recognized.
sharpness, of type boolean, defaulting to true
Whether sharpness constraining is recognized.
focusDistance, of type boolean, defaulting to true
Whether focus distance constraining is recognized.
tilt, of type boolean, defaulting to true
Whether tilt constraining is recognized.
zoom, of type boolean, defaulting to true
Whether configuration of the zoom level is recognized.
torch, of type boolean, defaulting to true
Whether configuration of torch is recognized.

9.2. MediaTrackCapabilities dictionary

MediaTrackCapabilities is extended here with the capabilities specific to image capture. This dictionary is produced by the UA via getCapabilities() and represents the supported ranges and enumerations of the supported constraints.

partial dictionary MediaTrackCapabilities {
  sequence<DOMString>  whiteBalanceMode;
  sequence<DOMString>  exposureMode;
  sequence<DOMString>  focusMode;

  MediaSettingsRange   exposureCompensation;
  MediaSettingsRange   exposureTime;
  MediaSettingsRange   colorTemperature;
  MediaSettingsRange   iso;

  MediaSettingsRange   brightness;
  MediaSettingsRange   contrast;
  MediaSettingsRange   saturation;
  MediaSettingsRange   sharpness;

  MediaSettingsRange   focusDistance;
  MediaSettingsRange   pan;
  MediaSettingsRange   tilt;
  MediaSettingsRange   zoom;

  boolean              torch;
};

9.2.1. Members

whiteBalanceMode, of type sequence<DOMString>
A sequence of supported white balance modes. Each string MUST be one of the members of MeteringMode.
colorTemperature, of type MediaSettingsRange
This range reflects the supported correlated color temperatures to be used for the scene white balance calculation.
exposureMode, of type sequence<DOMString>
A sequence of supported exposure modes. Each string MUST be the members of MeteringMode.
exposureCompensation, of type MediaSettingsRange
This reflects the supported range of exposure compensation. The supported range can be, and usually is, centered around 0 EV.
exposureTime, of type MediaSettingsRange
This reflects the supported range of exposure time. Values are numeric. Increasing values indicate increasing exposure time.
iso, of type MediaSettingsRange
This reflects the permitted range of ISO values.
focusMode, of type sequence<DOMString>
A sequence of supported focus modes. Each string MUST be one of the members of MeteringMode.
brightness, of type MediaSettingsRange
This reflects the supported range of brightness setting of the camera. Values are numeric. Increasing values indicate increasing brightness.
contrast, of type MediaSettingsRange
This reflects the supported range of contrast. Values are numeric. Increasing values indicate increasing contrast.
pan, of type MediaSettingsRange
This reflects the pan value range supported by the UA and by the track.

If the track has been created without requesting permission to use (as defined in [permissions]) a PermissionDescriptor with its name member set to camera and its panTiltZoom member set to true or if that permission request is denied, the track does not support pan. In that case the UA MUST NOT expose the pan value range.

saturation, of type MediaSettingsRange
This reflects the permitted range of saturation setting. Values are numeric. Increasing values indicate increasing saturation.
sharpness, of type MediaSettingsRange
This reflects the permitted sharpness range of the camera. Values are numeric. Increasing values indicate increasing sharpness, and the minimum value always implies no sharpness enhancement or processing.
focusDistance, of type MediaSettingsRange
This reflects the focus distance value range supported by the UA.
tilt, of type MediaSettingsRange
This reflects the tilt value range supported by the UA and by the track.

If the track has been created without requesting permission to use (as defined in [permissions]) a PermissionDescriptor with its name member set to camera and its panTiltZoom member set to true or if that permission request is denied, the track does not support tilt. In that case the UA MUST NOT expose the tilt value range.

zoom, of type MediaSettingsRange
This reflects the zoom value range supported by the UA and by the track.

If the track has been created without requesting permission to use (as defined in [permissions]) a PermissionDescriptor with its name member set to camera and its panTiltZoom member set to true or if that permission request is denied, the track does not support zoom. In that case the UA MUST NOT expose the zoom value range.

torch, of type boolean
A boolean indicating whether camera supports torch mode- on meaning supported.

9.3. MediaTrackConstraintSet dictionary

MediaTrackConstraintSet [GETUSERMEDIA] dictionary is used for both reading the current status with getConstraints() and for applying a set of constraints with applyConstraints().

MediaTrackSettings can be retrieved to verify the effect of the application by the user agent of the requested MediaTrackConstraints. Some constraints such as, e.g. zoom, might not be immediately applicable.
partial dictionary MediaTrackConstraintSet {
  ConstrainDOMString           whiteBalanceMode;
  ConstrainDOMString           exposureMode;
  ConstrainDOMString           focusMode;
  ConstrainPoint2D             pointsOfInterest;

  ConstrainDouble              exposureCompensation;
  ConstrainDouble              exposureTime;
  ConstrainDouble              colorTemperature;
  ConstrainDouble              iso;

  ConstrainDouble              brightness;
  ConstrainDouble              contrast;
  ConstrainDouble              saturation;
  ConstrainDouble              sharpness;

  ConstrainDouble              focusDistance;
  (boolean or ConstrainDouble) pan;
  (boolean or ConstrainDouble) tilt;
  (boolean or ConstrainDouble) zoom;

  ConstrainBoolean             torch;
};

9.3.1. Members

whiteBalanceMode, of type ConstrainDOMString
This string MUST be one of the members of MeteringMode. See white balance mode constrainable property.
exposureMode, of type ConstrainDOMString
This string MUST be one of the members of MeteringMode. See exposure constrainable property.
focusMode, of type ConstrainDOMString
This string MUST be one of the members of MeteringMode. See focus mode constrainable property.
colorTemperature, of type ConstrainDouble
See color temperature constrainable property.
exposureCompensation, of type ConstrainDouble
See exposure compensation constrainable property.
exposureTime, of type ConstrainDouble
See exposure time constrainable property.
iso, of type ConstrainDouble
See iso constrainable property.
pointsOfInterest, of type ConstrainPoint2D
See points of interest constrainable property.
brightness, of type ConstrainDouble
See brightness constrainable property.
contrast, of type ConstrainDouble
See contrast constrainable property.
pan, of type (boolean or ConstrainDouble)
A value of true is normalized to a value of empty ConstrainDoubleRange. A value of false is normalized to a value of undefined. See pan constrainable property.
saturation, of type ConstrainDouble
See saturation constrainable property.
sharpness, of type ConstrainDouble
See sharpness constrainable property.
focusDistance, of type ConstrainDouble
See focus distance constrainable property.
tilt, of type (boolean or ConstrainDouble)
A value of true is normalized to a value of empty ConstrainDoubleRange. A value of false is normalized to a value of undefined. See tilt constrainable property.
zoom, of type (boolean or ConstrainDouble)
A value of true is normalized to a value of empty ConstrainDoubleRange. A value of false is normalized to a value of undefined. See zoom constrainable property.
torch, of type ConstrainBoolean
See torch constrainable property.

9.4. MediaTrackSettings dictionary

When the getSettings() method is invoked on a video stream track, the user agent must return the extended MediaTrackSettings dictionary, representing the current status of the underlying user agent.

partial dictionary MediaTrackSettings {
  DOMString         whiteBalanceMode;
  DOMString         exposureMode;
  DOMString         focusMode;
  sequence<Point2D> pointsOfInterest;

  double            exposureCompensation;
  double            exposureTime;
  double            colorTemperature;
  double            iso;

  double            brightness;
  double            contrast;
  double            saturation;
  double            sharpness;

  double            focusDistance;
  double            pan;
  double            tilt;
  double            zoom;

  boolean           torch;
};

9.4.1. Members

whiteBalanceMode, of type DOMString
Current white balance mode setting. The string MUST be one of the members of MeteringMode.
exposureMode, of type DOMString
Current exposure mode setting. The string MUST be one of the members of MeteringMode.
colorTemperature, of type double
Color temperature in use for the white balance calculation of the scene. This field is only significant if whiteBalanceMode is manual.
exposureCompensation, of type double
Current exposure compensation setting. A value of 0 EV is interpreted as no exposure compensation. This field is only significant if exposureMode is continuous or single-shot
exposureTime, of type double
Current exposure time setting. This field is only significant if exposureMode is manual.
iso, of type double
Current camera ISO setting.
focusMode, of type DOMString
Current focus mode setting. The string MUST be one of the members of MeteringMode.
pointsOfInterest, of type sequence<Point2D>
A sequence of Point2Ds in use as points of interest for other settings, e.g. Focus, Exposure and Auto White Balance.
brightness, of type double
This reflects the current brightness setting of the camera.
contrast, of type double
This reflects the current contrast setting of the camera.
pan, of type double
This reflects the current pan setting of the camera.

If the track has been created without requesting permission to use (as defined in [permissions]) a PermissionDescriptor with its name member set to camera and its panTiltZoom member set to true or if that permission request is denied, the track does not support pan. In that case the UA MUST NOT expose the pan setting.

saturation, of type double
This reflects the current saturation setting of the camera.
sharpness, of type double
This reflects the current sharpness setting of the camera.
focusDistance, of type double
This reflects the current focus distance setting of the camera.
tilt, of type double
This reflects the current tilt setting of the camera.

If the track has been created without requesting permission to use (as defined in [permissions]) a PermissionDescriptor with its name member set to camera and its panTiltZoom member set to true or if that permission request is denied, the track does not support tilt. In that case the UA MUST NOT expose the tilt setting.

zoom, of type double
This reflects the current zoom setting of the camera.

If the track has been created without requesting permission to use (as defined in [permissions]) a PermissionDescriptor with its name member set to camera and its panTiltZoom member set to true or if that permission request is denied, the track does not support zoom. In that case the UA MUST NOT expose the zoom setting.

torch, of type boolean
Current camera torch configuration setting.

9.5. Additional Constrainable Properties

dictionary ConstrainPoint2DParameters {
  sequence<Point2D> exact;
  sequence<Point2D> ideal;
};

typedef (sequence<Point2D> or ConstrainPoint2DParameters) ConstrainPoint2D;

9.5.1. Members

exact, of type sequence<Point2D>
The exact required value of points of interest.
ideal, of type sequence<Point2D>
The ideal (target) value of points of interest.

10. Photo Capabilities and Constrainable Properties

Many of the mentioned photo and video capabilities mirror hardware features that are hard to define since can be implemented in a number of ways. Moreover, manufacturers tend to publish vague definitions to protect their intellectual property.
  1. White balance mode is a setting that cameras use to adjust for different color temperatures. Color temperature is the temperature of background light (usually measured in Kelvin). This setting can usually be automatically and continuously determined by the implementation, but it’s also common to offer a manual mode in which the estimated temperature of the scene illumination is hinted to the implementation. Typical temperature ranges for popular modes are provided below:
    Mode Kelvin range
    incandescent 2500-3500
    fluorescent 4000-5000
    warm-fluorescent 5000-5500
    daylight 5500-6500
    cloudy-daylight 6500-8000
    twilight 8000-9000
    shade 9000-10000
  2. Exposure is the amount of light that is allowed to fall on the photosensitive device. In auto-exposure modes (single-shot or continuous exposureMode), the exposure time and/or camera aperture are automatically adjusted by the implementation based on the subject of the photo. In manual exposureMode, these parameters are set to fixed absolute values.
  3. Focus mode describes the focus setting of the capture device (e.g. auto or manual).
  4. Points of interest describe the metering area centers used in other settings, e.g. exposure, white balance mode and focus mode each one being a Point2D (usually these three controls are modified simultaneously by the so-called 3A algorithm: auto-focus, auto-exposure, auto-white-balance).

    A Point2D Point of Interest is interpreted to represent a pixel position in a normalized square space ({x,y} &isin; [0.0, 1.0]). The origin of coordinates {x,y} = {0.0, 0.0} represents the upper leftmost corner whereas the {x,y} = {1.0, 1.0} represents the lower rightmost corner: the x coordinate (columns) increases rightwards and the y coordinate (rows) increases downwards. Values beyond the mentioned limits will be clamped to the closest allowed value.

  5. Exposure Compensation is a numeric camera setting that adjusts the exposure level from the current value used by the implementation. This value can be used to bias the exposure level enabled by auto-exposure, and usually is a symmetric range around 0 EV (the no-compensation value). This value is only used in single-shot and continuous exposureMode.
  6. Exposure Time is a numeric camera setting that controls the length of time during which light is allowed to fall on the photosensitive device. This value is used in manual exposureMode to control exposure. The value is in 100 microsecond units. That is, a value of 1.0 means an exposure time of 1/10000th of a second and a value of 10000.0 means an exposure time of 1 second.
  7. The ISO setting of a camera describes the sensitivity of the camera to light. It is a numeric value, where the lower the value the greater the sensitivity. This value should follow the [iso12232] standard.
  8. Red Eye Reduction is a feature in cameras that is designed to limit or prevent the appearance of red pupils ("Red Eye") in photography subjects due prolonged exposure to a camera’s flash.
  9. [LIGHTING-VOCABULARY] defines brightness as "the attribute of a visual sensation according to which an area appears to emit more or less light" and in the context of the present API, it refers to the numeric camera setting that adjusts the perceived amount of light emitting from the photo object. A higher brightness setting increases the intensity of darker areas in a scene while compressing the intensity of brighter parts of the scene. The range and effect of this setting is implementation dependent but in general it translates into a numerical value that is added to each pixel with saturation.
  10. Contrast is the numeric camera setting that controls the difference in brightness between light and dark areas in a scene. A higher contrast setting reflects an expansion in the difference in brightness. The range and effect of this setting is implementation dependent but it can be understood as a transformation of the pixel values so that the luma range in the histogram becomes larger; the transformation is sometimes as simple as a gain factor.
  11. [LIGHTING-VOCABULARY] defines saturation as "the colourfulness of an area judged in proportion to its brightness" and in the current context it refers to a numeric camera setting that controls the intensity of color in a scene (i.e. the amount of gray in the scene). Very low saturation levels will result in photos closer to black-and-white. Saturation is similar to contrast but referring to colors, so its implementation, albeit being platform dependent, can be understood as a gain factor applied to the chroma components of a given image.
  12. Sharpness is a numeric camera setting that controls the intensity of edges in a scene. Higher sharpness settings result in higher contrast along the edges, while lower settings result in less contrast and blurrier edges (i.e. soft focus). The implementation is platform dependent, but it can be understood as the linear combination of an edge detection operation applied on the original image and the original image itself; the relative weights being controlled by this sharpness.
    Brightness, contrast, saturation and sharpness are specified in [UVC].
  13. Image width and image height represent the supported/desired resolution of the resulting photographic image after any potential sensor corrections and other algorithms are run.
    The supported resolutions are managed segregated e.g. imageWidth and imageHeight values/ranges to prevent increasing the fingerprinting surface and to allow the UA to make a best-effort decision with regards to actual hardware configuration vis-a-vis requested constraints.
  14. Focus distance is a numeric camera setting that controls the focus distance of the lens. The setting usually represents distance in meters to the optimal focus distance.
  15. Pan is a numeric camera setting that controls the pan of the camera. The setting represents pan in arc seconds, which are 1/3600th of a degree. Values are in the range from -180*3600 arc seconds to +180*3600 arc seconds. Positive values pan the camera clockwise as viewed from above, and negative values pan the camera counter clockwise as viewed from above.

    Any algorithm which uses a MediaTrackConstraintSet object and its pan dictionary member which exists after a possible normalization MUST request permission to use (as defined in [permissions]) a PermissionDescriptor with its name member set to camera and its panTiltZoom member set to true, and, optionally, consider its deviceId member set to any appropriate device’s deviceId.

    If the visibilityState of the top-level browsing context value is "hidden", the applyConstraints() algorithm MUST throw a SecurityError if pan dictionary member exists after a possible normalization.

    The pan, tilt and zoom dictionary members exists after a possible normalization if the normalized value is a double value or a ConstrainDoubleRange value (whether empty or not). A boolean value of true is normalized to an empty ConstrainDoubleRange value thus the dictionary member exists after a normalization. A boolean value of false is normalized to no value thus the dictionary member does not exist after a normalization. An empty ConstrainDoubleRange value implies no constraints but only a permission and capability request.
  16. Tilt is a numeric camera setting that controls the tilt of the camera. The setting represents tilt in arc seconds, which are 1/3600th of a degree. Values are in the range from -180*3600 arc seconds to +180*3600 arc seconds. Positive values tilt the camera upward when viewed from the front, and negative values tilt the camera downward as viewed from the front.

    Any algorithm which uses a MediaTrackConstraintSet object and its tilt dictionary member which exists after a possible normalization MUST request permission to use (as defined in [permissions]) a PermissionDescriptor with its name member set to camera and its panTiltZoom member set to true, and, optionally, consider its deviceId member set to any appropriate device’s deviceId.

    If the visibilityState of the top-level browsing context value is "hidden", the applyConstraints() algorithm MUST throw a SecurityError if tilt dictionary member exists after a possible normalization.

    There is no defined order when applying pan and tilt, the UA is allowed to apply them in any order. In practice this should not matter since these values are absolute, so order will not affect the final position. However, if applying pan and tilt is slow enough, the order in which they are applied may be visually noticeable.
  17. Zoom is a numeric camera setting that controls the focal length of the lens. The setting usually represents a ratio, e.g. 4 is a zoom ratio of 4:1. The minimum value is usually 1, to represent a 1:1 ratio (i.e. no zoom).

    Any algorithm which uses a MediaTrackConstraintSet object and its zoom dictionary member which exists after a possible normalization MUST request permission to use (as defined in [permissions]) a PermissionDescriptor with its name member set to camera and its panTiltZoom member set to true, and, optionally, consider its deviceId member set to any appropriate device’s deviceId.

    If the visibilityState of the top-level browsing context value is "hidden", the applyConstraints() algorithm MUST throw a SecurityError if zoom dictionary member exists after a possible normalization.

  18. Fill light mode describes the flash setting of the capture device (e.g. auto, off, on). Torch describes the setting of the source’s fill light as continuously connected, staying on as long as track is active.

11. MeteringMode

enum MeteringMode {
  "none",
  "manual",
  "single-shot",
  "continuous"
};

11.1. Values

none
This source does not offer focus/exposure/white balance mode. For setting, this is interpreted as a command to turn off the feature.
manual
The capture device is set to manually control the lens position/exposure time/white balance, or such a mode is requested to be configured.
single-shot
The capture device is configured for single-sweep autofocus/one-shot exposure/white balance calculation, or such a mode is requested.
continuous
The capture device is configured for continuous focusing for near-zero shutter-lag/continuous auto exposure/white balance calculation, or such continuous focus hunting/exposure/white balance calculation mode is requested.

12. Point2D

A Point2D represents a location in a two dimensional space. The origin of coordinates is situated in the upper leftmost corner of the space.

dictionary Point2D {
  double x = 0.0;
  double y = 0.0;
};

12.1. Members

x, of type double, defaulting to 0.0
Value of the horizontal (abscissa) coordinate.
y, of type double, defaulting to 0.0
Value of the vertical (ordinate) coordinate.

13. Examples

Slightly modified versions of these examples can be found in e.g. this codepen collection.

13.1. Update camera pan, tilt and zoom and takePhoto()

The following example can also be found in e.g. this codepen with minimal modifications.
<html>
<body>
<video autoplay></video>
<img>
<div>
  <input id="pan" title="Pan" type="range" disabled />
  <label for="pan">Pan</label>
</div>
<div>
  <input id="tilt" title="Tilt" type="range" disabled />
  <label for="tilt">Tilt</label>
</div>
<div>
  <input id="zoom" title="Zoom" type="range" disabled />
  <label for="zoom">Zoom</label>
</div>
<script>
  let imageCapture;

  async function getMedia() {
    try {
      const stream = await navigator.mediaDevices.getUserMedia({
        video: {pan: true, tilt: true, zoom: true},
      });
      const video = document.querySelector('video');
      video.srcObject = stream;

      const [track] = stream.getVideoTracks();
      imageCapture = new ImageCapture(track);

      const capabilities = track.getCapabilities();
      const settings = track.getSettings();

      for (const ptz of ['pan', 'tilt', 'zoom']) {
        // Check whether pan/tilt/zoom is available or not.
        if (!(ptz in settings)) continue;

        // Map it to a slider element.
        const input = document.getElementById(ptz);
        input.min = capabilities[ptz].min;
        input.max = capabilities[ptz].max;
        input.step = capabilities[ptz].step;
        input.value = settings[ptz];
        input.disabled = false;
        input.oninput = async event => {
          try {
            // Warning: Chrome requires advanced constraints.
            await track.applyConstraints({[ptz]: input.value});
          } catch (err) {
            console.error("applyConstraints() failed: ", err);
          }
        };
      }
    } catch (err) {
      console.error(err);
    }
  }

  async function takePhoto() {
    try {
      const blob = await imageCapture.takePhoto();
      console.log("Photo taken: " + blob.type + ", " + blob.size + "B");

      const image = document.querySelector('img');
      image.src = URL.createObjectURL(blob);
    } catch (err) {
      console.error("takePhoto() failed: ", err);
    }
  }
</script>
</body>
</html>

13.2. Repeated grabbing of a frame with grabFrame()

The following example can also be found in e.g. this codepen with minimal modifications.
<html>
<body>
<canvas></canvas>
<button id="stopButton">Stop frame grab</button>
<script>
  async function grabFrames() {
    try {
      const canvas = document.querySelector('canvas');
      const video = document.querySelector('video');

      const stream = await navigator.mediaDevices.getUserMedia({video: true});
      video.srcObject = stream;
      const [track] = stream.getVideoTracks();
      try {
        const imageCapture = new ImageCapture(track);

        stopButton.onclick = () => track.stop();

        while (track.readyState == 'live') {
          const imgData = await imageCapture.grabFrame();
          canvas.width = imgData.width;
          canvas.height = imgData.height;
          canvas.getContext('2d').drawImage(imgData, 0, 0);
          await new Promise(r => setTimeout(r, 1000));
        }
      } finally {
        track.stop();
      }
    } catch (err) {
      console.error(err);
    }
  }
</script>
</body>
</html>

13.3. Grabbing a Frame and Post-Processing

The following example can also be found in e.g. this codepen with minimal modifications.
<html>
<body>
<canvas></canvas>
<script>
  async function grabFrames() {
    try {
      const canvas = document.querySelector('canvas');
      const video = document.querySelector('video');

      const stream = await navigator.mediaDevices.getUserMedia({video: true});
      video.srcObject = stream;
      const [track] = stream.getVideoTracks();
      try {
        const imageCapture = new ImageCapture(track);
        const imageBitmap = await imageCapture.grabFrame();

        // |imageBitmap| pixels are not directly accessible: we need to paint
        // the grabbed frame onto a <canvas>, then getImageData() from it.
        const ctx = canvas.getContext('2d');
        canvas.width = imageBitmap.width;
        canvas.height = imageBitmap.height;
        ctx.drawImage(imageBitmap, 0, 0);

        // Read back the pixels from the <canvas>, and invert the colors.
        const imageData = ctx.getImageData(0, 0, canvas.width, canvas.height);

        const data = imageData.data;
        for (let i = 0; i < data.length; i += 4) {
          data[i] ^= 255;     // red
          data[i + 1] ^= 255; // green
          data[i + 2] ^= 255; // blue
        }
        // Finally, draw the inverted image to the <canvas>
        ctx.putImageData(imageData, 0, 0);
      } finally {
        track.stop();
      }
    } catch (err) {
      console.error(err);
    }
  }
</script>
</body>
</html>

13.4. Update camera focus distance and takePhoto()

<html>
<body>
<video autoplay></video>
<img>
<input type="range" hidden>
<script>
  let imageCapture;

  async function getMedia() {
    try {
      const stream = await navigator.mediaDevices.getUserMedia({video: true});
      const video = document.querySelector('video');
      video.srcObject = stream;

      const [track] = stream.getVideoTracks();
      imageCapture = new ImageCapture(track);

      const capabilities = track.getCapabilities();
      const settings = track.getSettings();

      // Check whether focus distance is available or not.
      if (!capabilities.focusDistance) {
        return;
      }

      // Map focus distance to a slider element.
      const input = document.querySelector('input[type="range"]');
      input.min = capabilities.focusDistance.min;
      input.max = capabilities.focusDistance.max;
      input.step = capabilities.focusDistance.step;
      input.value = settings.focusDistance;
      input.oninput = async event => {
        try {
          await track.applyConstraints({
            focusMode: "manual",
            focusDistance: input.value
          });
        } catch (err) {
          console.error("applyConstraints() failed: ", err);
        }
      };
      input.parentElement.hidden = false;
    } catch (err) {
      console.error(err);
    }
  }

  async function takePhoto() {
    try {
      const blob = await imageCapture.takePhoto();
      console.log("Photo taken: " + blob.type + ", " + blob.size + "B");

      const image = document.querySelector('img');
      image.src = URL.createObjectURL(blob);
    } catch (err) {
      console.error("takePhoto() failed: ", err);
    }
  }
</script>
</body>
</html>

Conformance

Document conventions

Conformance requirements are expressed with a combination of descriptive assertions and RFC 2119 terminology. The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “MAY”, and “OPTIONAL” in the normative parts of this document are to be interpreted as described in RFC 2119. However, for readability, these words do not appear in all uppercase letters in this specification.

All of the text of this specification is normative except sections explicitly marked as non-normative, examples, and notes. [RFC2119]

Examples in this specification are introduced with the words “for example” or are set apart from the normative text with class="example", like this:

This is an example of an informative example.

Informative notes begin with the word “Note” and are set apart from the normative text with class="note", like this:

Note, this is an informative note.

Conformant Algorithms

Requirements phrased in the imperative as part of algorithms (such as "strip any leading space characters" or "return false and abort these steps") are to be interpreted with the meaning of the key word ("must", "should", "may", etc) used in introducing the algorithm.

Conformance requirements phrased as algorithms or specific steps can be implemented in any manner, so long as the end result is equivalent. In particular, the algorithms defined in this specification are intended to be easy to understand and are not intended to be performant. Implementers are encouraged to optimize.

Index

Terms defined by this specification

Terms defined by reference

References

Normative References

[FileAPI]
Marijn Kruisselbrink; Arun Ranganathan. File API. 11 September 2019. WD. URL: https://www.w3.org/TR/FileAPI/
[GETUSERMEDIA]
Cullen Jennings; et al. Media Capture and Streams. 4 November 2020. CR. URL: https://www.w3.org/TR/mediacapture-streams/
[HTML]
Anne van Kesteren; et al. HTML Standard. Living Standard. URL: https://html.spec.whatwg.org/multipage/
[PERMISSIONS]
Mounir Lamouri; Marcos Caceres; Jeffrey Yasskin. Permissions. 20 July 2020. WD. URL: https://www.w3.org/TR/permissions/
[RFC2119]
S. Bradner. Key words for use in RFCs to Indicate Requirement Levels. March 1997. Best Current Practice. URL: https://tools.ietf.org/html/rfc2119
[WebIDL]
Boris Zbarsky. Web IDL. 15 December 2016. ED. URL: https://heycam.github.io/webidl/

Informative References

[ISO12232]
Photography - Digital still cameras - Determination of exposure index, ISO speed ratings, standard output sensitivity, and recommended exposure index. 15 April 2006. URL: http://www.iso.org/iso/catalogue_detail.htm?csnumber=37777
[LIGHTING-VOCABULARY]
CIE International Lighting Vocabulary: IEC International Electrotechnical Vocabulary.. 15 December 1987.
[UVC]
USB Device Class Definition for Video Devices. 9 August 2012. URL: http://www.usb.org/developers/docs/devclass_docs/

IDL Index

[Exposed=Window]
interface ImageCapture {
   constructor(MediaStreamTrack videoTrack);
   Promise<Blob>              takePhoto(optional PhotoSettings photoSettings = {});
   Promise<PhotoCapabilities> getPhotoCapabilities();
   Promise<PhotoSettings>     getPhotoSettings();

   Promise<ImageBitmap>       grabFrame();

   readonly attribute MediaStreamTrack track;
};

dictionary PhotoCapabilities {
  RedEyeReduction         redEyeReduction;
  MediaSettingsRange      imageHeight;
  MediaSettingsRange      imageWidth;
  sequence<FillLightMode> fillLightMode;
};

dictionary PhotoSettings {
  FillLightMode   fillLightMode;
  double          imageHeight;
  double          imageWidth;
  boolean         redEyeReduction;
};

dictionary MediaSettingsRange {
    double max;
    double min;
    double step;
};

enum RedEyeReduction {
  "never",
  "always",
  "controllable"
};

enum FillLightMode {
  "auto",
  "off",
  "flash"
};

partial dictionary MediaTrackSupportedConstraints {
  boolean whiteBalanceMode = true;
  boolean exposureMode = true;
  boolean focusMode = true;
  boolean pointsOfInterest = true;

  boolean exposureCompensation = true;
  boolean exposureTime = true;
  boolean colorTemperature = true;
  boolean iso = true;

  boolean brightness = true;
  boolean contrast = true;
  boolean pan = true;
  boolean saturation = true;
  boolean sharpness = true;
  boolean focusDistance = true;
  boolean tilt = true;
  boolean zoom = true;
  boolean torch = true;
};

partial dictionary MediaTrackCapabilities {
  sequence<DOMString>  whiteBalanceMode;
  sequence<DOMString>  exposureMode;
  sequence<DOMString>  focusMode;

  MediaSettingsRange   exposureCompensation;
  MediaSettingsRange   exposureTime;
  MediaSettingsRange   colorTemperature;
  MediaSettingsRange   iso;

  MediaSettingsRange   brightness;
  MediaSettingsRange   contrast;
  MediaSettingsRange   saturation;
  MediaSettingsRange   sharpness;

  MediaSettingsRange   focusDistance;
  MediaSettingsRange   pan;
  MediaSettingsRange   tilt;
  MediaSettingsRange   zoom;

  boolean              torch;
};

partial dictionary MediaTrackConstraintSet {
  ConstrainDOMString           whiteBalanceMode;
  ConstrainDOMString           exposureMode;
  ConstrainDOMString           focusMode;
  ConstrainPoint2D             pointsOfInterest;

  ConstrainDouble              exposureCompensation;
  ConstrainDouble              exposureTime;
  ConstrainDouble              colorTemperature;
  ConstrainDouble              iso;

  ConstrainDouble              brightness;
  ConstrainDouble              contrast;
  ConstrainDouble              saturation;
  ConstrainDouble              sharpness;

  ConstrainDouble              focusDistance;
  (boolean or ConstrainDouble) pan;
  (boolean or ConstrainDouble) tilt;
  (boolean or ConstrainDouble) zoom;

  ConstrainBoolean             torch;
};

partial dictionary MediaTrackSettings {
  DOMString         whiteBalanceMode;
  DOMString         exposureMode;
  DOMString         focusMode;
  sequence<Point2D> pointsOfInterest;

  double            exposureCompensation;
  double            exposureTime;
  double            colorTemperature;
  double            iso;

  double            brightness;
  double            contrast;
  double            saturation;
  double            sharpness;

  double            focusDistance;
  double            pan;
  double            tilt;
  double            zoom;

  boolean           torch;
};

dictionary ConstrainPoint2DParameters {
  sequence<Point2D> exact;
  sequence<Point2D> ideal;
};

typedef (sequence<Point2D> or ConstrainPoint2DParameters) ConstrainPoint2D;

enum MeteringMode {
  "none",
  "manual",
  "single-shot",
  "continuous"
};

dictionary Point2D {
  double x = 0.0;
  double y = 0.0;
};