[GEM-dev] pix_chroma_key not acting as I expect?

[B. Bogart]

Hi all,

attached is what I ended up getting to work.

#1. loading the video as rgb indeed messes up how pix_chroma_key works, I
can't really describe how, but I had to make sure the videos were loading
as yuv for it to work at all. Teresa, on OSX this is the default so don't
worry about it.

#2. Chris's 128, 50,50 value for the RGB 0,240,0 seems to work, but where
the heck did that number come from??

#3. I had to use a high range, about 80, but I think thats because of
antialiasing between the green-screen and the figure.

So it looks good!

I can't do a checkout from sourceforge gem cvs this morning, but based on
Johannes's new abstractions, I'd like to volunteer to make a keying
color-picker. Maybe something that shows your video, allows you to click
on a spot, and then feeds that into pix_chroma_key. Maybe even a range of
pixels could be chosen.

I think the only way to get the pixel values is pix_dump right? Does it
support dumping YUV?

Thanks all for your help.

.b.

On Wed, April 26, 2006 1:03 am, Teresa Ascencao said:
> thanks so much for all that you have been helping me with!  I really
> appreciate it.
>
> teresa ascencao
> www.tascencao.com
> 416-929-6854
>
>
> On 25-Apr-06, at 3:07 PM, Mathieu Bouchard wrote:
>
>> On Tue, 25 Apr 2006, chris clepper wrote:
>>
>>> On 4/25/06, B. Bogart <ben at ekran.org> wrote:
>>>>  I still could not get pix_chroma_key to key on "value 16,16,16"
>>>> remember
>>>> our green is 0,240,0 not 0,255,0. (which I guess is YUV 0,0,0)? what
>>>> should the YUV range be like for this video?
>>> I may have bungled some of the code in that object.  Try 128, 50, 50
>>> and a range of 30 or so for a green background.  I was able to key out
>>> a fairly typical green screen with that.
>>
>> there's [rgb2hsv], [hsv2rgb], but do [rgb2yuv] and [yuv2rgb] exist yet?
>>
>> There's [#rgb_to_yuv] and [#yuv_to_rgb] which works for both single
>> pixels
>> and whole pictures, but they use JPEG-style yuv, which goes 0..255
>> instead
>> of the legacy range 16..239 (and such) which are due to NTSC/PAL
>> voltage
>> specifications. (Both ranges of YUV are in wide use).
>>
>>  _ _ __ ___ _____ ________ _____________ _____________________ ...
>> | Mathieu Bouchard - tél:+1.514.383.3801 - http://artengine.ca/matju
>> | Freelance Digital Arts Engineer, Montréal QC Canada
>>
>
>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: chroma_key.pd
Type: application/octet-stream
Size: 2696 bytes
Desc: not available
URL: <http://lists.puredata.info/pipermail/gem-dev/attachments/20060426/87669a5a/attachment.obj>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: chroma_key.pd
Type: application/octet-stream
Size: 2696 bytes
Desc: not available
URL: <http://lists.puredata.info/pipermail/gem-dev/attachments/20060426/87669a5a/attachment-0001.obj>