W3C home > Mailing lists > Public > public-media-capture@w3.org > December 2011

Re: use cases not covered by media capture under DAP

From: Rich Tibbett <richt@opera.com>
Date: Thu, 01 Dec 2011 01:50:48 +0100
Message-ID: <4ED6CF68.3000206@opera.com>
To: Brian LeRoux <b@brian.io>
CC: public-media-capture@w3.org
Brian LeRoux wrote:
> Hey guys, I'm Brian and I work on the PhoneGap project. [1] We
> implemented Media Capture. [2] It doesn't cover a number of use cases
> so we have a complementary API of our own utility that covers the
> common cases for image capturing discovered by PhoneGap app authors.
> [3]
> Perhaps these real world cases can be of use.
> In particular things we see all the time:
> - image source (many camera sensors common now, select from photo
> lib/gallary VERY common)

The HTML Media Capture spec does provide an easy way to obtain 1 or more 
photo/video/audio files from a file system:


Would this gallery/lib 'capture' need to be real-time for any reason, 
and therefore manifest itself as a programmatic API for this purpose or 
would the above suffice?

> - image destination (local to app, to the SD card, filesystem, as base64 string)

'Download to save' is something the majority of web users are familiar 
with today. When that mechanism gets triggered (by a user clicking a 
downloadable file) then files on the web don't have a destination per 
se. It's very much up to the user at the point of download where they 
want to save that file.

It might be nice to provide a destination hint for a downloadable file 
but I'm uncertain on the exact use cases for that at this point.

Alternatively, we could store all capture data in a common directory on 
the user's filesystem - so if required the user can go to that common 
file system location (e.g. ~/Pictures/web/) and obtain their generated 
image/audio/video data - or a native application can programmatically 
obtain files from that location since it always knows where to look.

> - image quality

If you copy the image data to a canvas element you can then get a data 
URI or blob where you can specify the desired encoding and quality e.g.

canvas.toDataURL('image/jpeg', 0.6);
// or
canvas.toBlob(function(blob) {}, 'image/jpeg', 0.2);

> - image rotation

If you copy the image data to a canvas element and then obtain its 2D 
context you can then call rotate() on that context object to rotate the 
displayed 'image'. You can then obtain the manipulated image back via 
toDataURL or toBlob as above if you want to generate a file-like object 
that you can then pass around as required.

> - image encoding

See image quality above.


I wanted to record the above points in the discussion. I do like the 
efficacy of canvas to achieve any desired image manipulation (and soon 
to also be capable of audio manipulation).

- Rich

> [1] http://phonegap.com
> [2] http://docs.phonegap.com/en/1.2.0/phonegap_media_capture_capture.md.html#Capture
> [3] http://docs.phonegap.com/en/1.2.0/phonegap_camera_camera.md.html#Camera
Received on Thursday, 1 December 2011 00:51:38 UTC

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