Re: [Playerstage-developers] Stage 2.1 SVN: What happend to blobfinder model?

[Paul O. <new...@ki...>]

On Sat, 8 Nov 2008, Geoffrey Biggs wrote:

> I did a bit of quick research, and it looks like Stage is the correct
> one here. 0xFF in the alpha channel is understood as fully opaque by the
> PNG standard, the CSS3 standard, and OpenGL (the last being what Stage
> uses), so that seems to be the convention.
>
> The blobfinder interface description doesn't say that it returns an ARGB
> colour, but rather an RGB colour with the 3 values 32-bit packed,
> leaving 8 bits on the end. I think the intention is that it returns an
> RGB value, and the remaining 8 bits should be ignored for the purposes
> of colour matching. Cameras are not likely to return a transparency
> channel, anyway. I think the documentation should be clarified rather
> than patching Stage.
>
> Geoff
>

This page here: 
http://playerstage.sourceforge.net/doc/Player-cvs/player/structplayer__blobfinder__blob.html 
explicitly says: "The color is stored as packed 32-bit RGB, i.e., 
0x00RRGGBB.", so recently, Stage's blobfinder is incompatible with that. I 
guess it is a result of turnign Stage into OpenGL (through FLTK), however 
I see no reason for doing that for 2.1 branch. My patch (on a tracker) for 
Stage-2.1 branch at least reverts old behaviour. Let's leave new troubles 
for new versions.
Paul

> Paul Osmialowski wrote:
>>
>> On Sat, 8 Nov 2008, Geoffrey Biggs wrote:
>>
>>> The 0xFF000000 is probably setting the alpha channel of an ARGB colour.
>>> Whether 0xFF or 0x00 is correct, I don't know. Probably the value you
>>> have for cyan thinks that 0x00 is fully opaque, while stage thinks that
>>> 0xFF is fully opaque. Is that value for cyan something coded into the
>>> blobfinder drivers?
>>>
>>> Geoff
>>>
>>
>> Not in the code but in the manual, see description of blobfinder interface
>> it says it returns color values as 0x00RRGGBB. And all my programs were
>> written according to that. Also most of the 32-bit graphics programs I
>> ever seen used 0 for alpha channel when it is fully opaque. Proposed patch
>> solves this incompability between stages perception of opacity and
>> blobfinder interface documentation.
>> Paul
>
>
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