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Re: [depth] depth value encoding proposal

From: Harald Alvestrand <harald@alvestrand.no>
Date: Tue, 19 Aug 2014 21:31:35 +0200
Message-ID: <53F3A617.6020905@alvestrand.no>
To: public-media-capture@w3.org
On 08/19/2014 06:01 PM, Benjamin Schwartz wrote:
> On Tue, Aug 19, 2014 at 10:58 AM, Kostiainen, Anssi
> <anssi.kostiainen@intel.com <mailto:anssi.kostiainen@intel.com>> wrote:
>     Hi Benjamin,
>     Thanks for your comments, and sorry for the late reply due to the
>     vacation period.
>     I noticed the following comments (1) and (2) you’ve made, and
>     would like to check the status, and ask your help to fill in the
>     gaps if any:
>     (1) "I do not think this kind of arbitrary mapping is appropriate
>     in a W3C standard.  We should arrange for a natural representation
>     instead, with modifications to Canvas and WebGL if necessary.” [1]
>     To make sure I understood this correctly:
>     Firstly, you're proposing we patch the CanvasRenderingContext2D
>     and make ImageData.data of type ArrayBufferView instead of
>     Uint8ClampedArray to allow the Uint16Array type, correct? Better
>     suggestions?
> I would suggest going all the way to Float32 as well. 
>     Secondly, extend the WebGLRenderingContext along the lines of the
>     LUMINANCE16 extension proposal [2] -- or would you prefer to use
>     the depth component of a GL texture as you previously suggested?
>     Known issues? I’d like to hear your latest thoughts on this and if
>     possible a concrete proposal how you’d prefer this to be spec’d to
>     be practical for developers and logical for implementers.
> I'd strongly prefer to use a depth component (and also have an option
> to use 32-bit float).  This would raise the GLES version requirement
> for WebGL, but I think this is not an unreasonable requirement for a
> feature that also requires a depth camera!
>     (2) "I don't think getDepthTracks() should return color-video.  If
>     you want to prototype using depth-to-color mappings, the logical
>     way is to treat the depth channel as a distinct color video
>     camera, accessible by the usual device selection mechanisms.” [3]
>     This is what the spec currently says re getDepthTracks():
>     [[
>     The getDepthTracks() method, when invoked, must return a sequence
>     of MediaStreamTrack objects representing the depth tracks in this
>     stream.
>     The getDepthTracks() method must return a sequence that represents
>     a snapshot of all the MediaStreamTrack objects in this stream's
>     track set whose kind is equal to "depth". The conversion from the
>     track set to the sequence is user agent defined and the order does
>     not have to be stable between calls.
>     ]]
>     Do you have a concrete proposal how you’d tighten the prose to
>     clear the confusion?
> I would not include |getDepthTracks| until we have a depth datatype.
>  Instead, I would add each depth camera as an input device of kind:
> 'video' in the list returned by enumerateDevices(), with its label
> containing a human-readable indication that its color video data is
> computed from depth via a mapping defined by the user agent.

But once this spec is implemented, we have a depth datatype.... or did I
misunderstand the proposal?

I'm afraid that if we spec out a path where depth is treated as a weird
kind of video, we'll never escape from it - so I'm happy to see such a
fully-worked proposal that includes both the depth datatype and the
depth track definition.
Received on Tuesday, 19 August 2014 19:32:09 UTC

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