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This document specifies the takePhoto()and grabFrame()methods, and corresponding camera settings for use with MediaStreamTracks (as defined in Media Capture and Streams [GETUSERMEDIA]).
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This document was published by the Device and Sensors Working Group and the Web Real-Time Communications Working Group as a Working Draft. This document is intended to become a W3C Recommendation. If you wish to make comments regarding this document, please send them to public-media-capture@w3.org (subscribe, archives). All comments are welcome.
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This document is governed by the 1 September 2015 W3C Process Document.
The API defined in this document captures images from a valid MediaStreamTrack. The produced image can be in the form of a Blob (as defined in [FILE-API]) or as an ImageBitmap (as defined in [HTML51])). The source image is provided by the capture device that provides the MediaStreamTrack. Moreover, picture-specific settings can be optionally provided as arguments that can be applied to the device for the capture.
The User Agent must support Promises in order to implement the Image Capture API. Any Promise object is assumed to have resolver object, with resolve() and reject() methods associated with it.
[Constructor(MediaStreamTrack track)]
interface ImageCapture {
readonly attribute MediaStreamTrack videoStreamTrack;
readonly attribute MediaStream previewStream;
Promise<PhotoCapabilities> getPhotoCapabilities();
Promise<void> setOptions(PhotoSettings? photoSettings);
Promise<Blob> takePhoto(PhotoSettings? photoSettings);
Promise<ImageBitmap> grabFrame();
};ImageCapture| Parameter | Type | Nullable | Optional | Description |
|---|---|---|---|---|
| track | MediaStreamTrack |
✘ | ✘ | The MediaStreamTrack to be used as source of data. This will be the value of the videoStreamTrack attribute. The MediaStreamTrack passed to the constructor MUST have its kind attribute set to "video" otherwise a DOMException of type NotSupportedError will be thrown. |
videoStreamTrack of type MediaStreamTrack, readonlypreviewStream of type MediaStream, readonlygetPhotoCapabilitiesgetPhotoCapabilities() method of an ImageCapture object is invoked, a new Promise is returned. If the UA is unable to execute the getPhotoCapabilities() method for any reason (for example, the MediaStreamTrack being ended asynchronously), then the UA MUST return a promise rejected with a newly created ImageCaptureError with the appropriate errorDescription set. Otherwise it MUST queue a task, using the DOM manipulation task source, that runs the following steps:
MediaStreamTrack into a PhotoCapabilities object containing the available capabilities of the device, including ranges where appropriate. The resolved PhotoCapabilities will also include the current conditions in which the capabilities of the device are found. The method of doing this will depend on the underlying device. PhotoCapabilities object.setOptionssetOptions() method of an ImageCapture object is invoked, then a valid PhotoSettings object MUST be passed in the method to the ImageCapture object. In addition, a new Promise object is returned. If the UA can successfully apply the settings, then the UA MUST return a resolved promise. If the UA cannot successfully apply the settings, then the UA MUST return a promise rejected with a newly created ImageCaptureError whose errorDescription is set to OPTIONS_ERROR. If the UA can successfully apply the settings, the effect MAY be reflected, if visible at all, in previewStream| Parameter | Type | Nullable | Optional | Description |
|---|---|---|---|---|
| type | PhotoSettings |
✔ | ✘ |
The PhotoSettings dictionary to be applied.
|
takePhototakePhoto() method of an ImageCapture object is invoked, a new Promise object is returned. If the readyState of the VideoStreamTrack provided in the constructor is not "live", the UA MUST return a promise rejected with a newly created ImageCaptureError object whose errorDescription is set to INVALID_TRACK. If the UA is unable to execute the takePhoto() method for any other reason (for example, upon invocation of multiple takePhoto() method calls in rapid succession), then the UA MUST return a promise rejected with a newly created ImageCaptureError object whose errorDescription is set to PHOTO_ERROR. Otherwise it MUST queue a task, using the DOM manipulation task source, that runs the following steps:
undefined.setOptions() had been called immediately before takePhoto()). If the UA cannot successfully apply the settings, then the UA MUST return a promise rejected with a newly created ImageCaptureError whose errorDescription is set to OPTIONS_ERROR.MediaStreamTrack 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 mute and unmute events to fire on the Track in question. | Parameter | Type | Nullable | Optional | Description |
|---|---|---|---|---|
| type | PhotoSettings |
✔ | ✔ |
The PhotoSettings dictionary to be applied.
|
grabFramegrabFrame() method of an ImageCapture object is invoked, a new Promise object is returned. If the readyState of the MediaStreamTrack provided in the contructor is not "live", the UA MUST return a promise rejected with a newly created ImageCaptureError object whose errorDescription is set to INVALID_TRACK. If the UA is unable to execute the grabFrame() method for any other reason, then the UA MUST return a promise rejected with a newly created ImageCaptureError object whose errorDescription is set to FRAME_ERROR. Otherwise it MUST queue a task, using the DOM manipulation task source, that runs the following steps:
MediaStreamTrack into an ImageBitmap object (as defined in [HTML51]). The width and height of the ImageBitmap object are derived from the constraints of the MediaStreamTrack. ImageBitmap object. (Note: grabFrame() returns data only once upon being invoked).ImageCaptureError[NoInterfaceObject]
interface ImageCaptureError {
readonly attribute DOMString? errorDescription;
};errorDescription of type DOMString?, readonlyerrorDescription attribute returns the appropriate DOMString for the error description. Acceptable values are FRAME_ERROR, OPTIONS_ERROR, PHOTO_ERROR, INVALID_TRACK, and ERROR_UNKNOWN.PhotoCapabilitiesinterface PhotoCapabilities {
readonly attribute MeteringMode whiteBalanceMode;
readonly attribute unsigned long colorTemperature;
readonly attribute MeteringMode exposureMode;
readonly attribute MediaSettingsRange exposureCompensation;
readonly attribute MediaSettingsRange iso;
readonly attribute boolean redEyeReduction;
readonly attribute MeteringMode focusMode;
readonly attribute MediaSettingsRange brightness;
readonly attribute MediaSettingsRange contrast;
readonly attribute MediaSettingsRange saturation;
readonly attribute MediaSettingsRange sharpness;
readonly attribute MediaSettingsRange imageHeight;
readonly attribute MediaSettingsRange imageWidth;
readonly attribute MediaSettingsRange zoom;
readonly attribute FillLightMode fillLightMode;
};whiteBalanceMode of type MeteringModecolorTemperature of type unsigned longwhiteBalanceMode is manual.exposureMode of type MeteringModeexposureCompensation of type MediaSettingsRangeiso of type MediaSettingsRangeredEyeReduction of type booleanfocusMode of type MeteringModebrightness of type MediaSettingsRangecontrast of type MediaSettingsRangesaturation of type MediaSettingsRangesharpness of type MediaSettingsRangeimageHeight of type MediaSettingsRangeimageWidth of type MediaSettingsRangezoom of type MediaSettingsRangefillLightMode of type FillLightModeFillLightMode.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.
This section is non-normative.
The PhotoCapabilities interface provides the photo-specific settings options and current settings values. The following definitions are assumed for individual settings and are provided for information purposes:
manual mode in which the estimated temperature of the scene illumination is hinted to the implementation. Typical temperature ranges for popular mode 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 |
auto or manual). auto, off, on). PhotoSettingsThe PhotoSettings object is optionally passed into the setOptions() method in order to modify capture device settings specific to still imagery. Each of the attributes in this object is optional.
dictionary PhotoSettings {
MeteringMode whiteBalanceMode;
unsigned long colorTemperature;
MeteringMode exposureMode;
unsigned long exposureCompensation;
unsigned long iso;
boolean redEyeReduction;
MeteringMode focusMode;
sequence<Point2D> pointsOfInterest;
unsigned long brightness;
unsigned long contrast;
unsigned long saturation;
unsigned long sharpness;
unsigned long zoom;
unsigned long imageHeight;
unsigned long imageWidth;
FillLightMode fillLightMode;
};whiteBalanceMode of type MeteringModecolorTemperature of type unsigned longwhiteBalanceMode is manual.exposureMode of type MeteringModeMeteringMode.exposureCompensation of type unsigned long, multiplied by 100 (to avoid using floating point). iso of type unsigned longredEyeReduction of type booleanfocusMode of type MeteringModeMeteringMode.pointsOfInterest of type sequence<Point2D>sequence of Point2Ds to be used as metering area centers for other settings, e.g. Focus, Exposure and Auto White Balance.brightness of type unsigned longcontrast of type unsigned longsaturation of type unsigned longsharpness of type unsigned longzoom of type unsigned longimageHeight of type unsigned longimageWidth of type unsigned longfillLightMode of type FillLightModeFillLightMode.MediaSettingsRangeinterface MediaSettingsRange {
readonly attribute long max;
readonly attribute long min;
readonly attribute long current;
};max of type long, readonlymin of type long, readonlycurrent of type long, readonlyFillLightModeenum FillLightMode {
"unavailable",
"auto",
"off",
"flash",
"on"
};unavailableautoflash to guarantee firing of the flash for the takePhoto() or getFrame() methods.offflashtakePhoto() or getFrame() methods. onMediaStreamTrack is activeMeteringModeNote that MeteringMode is used for both status enumeration and for setting options for capture(s).
enum MeteringMode {
"none",
"manual",
"single-shot",
"continuous"
};nonemanualsingle-shotcontinuousPoint2DA Point2D represents a location in a normalized square space with values in [0.0, 1.0].
x of type floaty of type floatThis section is non-normative.
navigator.mediaDevices.getUserMedia({video: true}).then(gotMedia, failedToGetMedia);
function gotMedia(mediastream) {
// Extract video track.
var videoTrack = mediastream.getVideoTracks()[0];
// Check if this device supports a picture mode...
var captureDevice = new ImageCapture(videoTrack);
if (captureDevice) {
captureDevice.grabFrame().then(processFrame(imgData));
}
}
function processFrame(e) {
imgData = e.imageData;
width = imgData.width;
height = imgData.height;
for (j = 3; j < imgData.width; j += 4) {
// Set all alpha values to medium opacity
imgData.data[j] = 128;
}
// Create new ImageObject with the modified pixel values
var canvas = document.createElement('canvas');
ctx = canvas.getContext("2d");
newImg = ctx.createImageData(width,height);
for (j = 0; j < imgData.width; j++) {
newImg.data[j] = imgData.data[j];
}
// ... and do something with the modified image ...
}
}
function failedToGetMedia(e) {
console.log('Stream failure: ' + e);
}navigator.mediaDevices.getUserMedia({video: true}).then(gotMedia, failedToGetMedia);
function gotMedia(mediastream) {
// Extract video track.
var videoDevice = mediastream.getVideoTracks()[0];
// Check if this device supports a picture mode...
var captureDevice = new ImageCapture(videoDevice);
if (captureDevice) {
if (captureDevice.photoCapabilities.redEyeReduction) {
captureDevice.setOptions({redEyeReductionSetting:true})
.then(captureDevice.takePhoto()
.then(showPicture(blob),function(error){alert("Failed to take photo");}));
} else {
console.log('No red eye reduction');
}
}
}
function showPicture(e) {
var img = document.querySelector("img");
img.src = URL.createObjectURL(e.data);
}
function failedToGetMedia(e) {
console.log('Stream failure: ' + e);
}<html>
<body>
<p><canvas id="frame"></canvas></p>
<button onclick="stopFunction()">Stop frame grab</button>
<script>
var canvas = document.getElementById('frame');
navigator.mediaDevices.getUserMedia({video: true}).then(gotMedia, failedToGetMedia);
function gotMedia(mediastream) {
// Extract video track.
var videoDevice = mediastream.getVideoTracks()[0];
// Check if this device supports a picture mode...
var captureDevice = new ImageCapture(videoDevice);
var frameVar;
if (captureDevice) {
frameVar = setInterval(captureDevice.grabFrame().then(processFrame()), 1000);
}
}
function processFrame(e) {
imgData = e.imageData;
canvas.width = imgData.width;
canvas.height = imgData.height;
canvas.getContext('2d').drawImage(imgData, 0, 0, imgData.width, imgData.height);
}
function stopFunction(e) {
clearInterval(myVar);
}
function failedToGetMedia(e) {
console.log('Stream failure: ' + e);
}
</script>
</body>
</html>