Hi pure people,
I am new to pure but an experienced software developer.
I use PD for an interactive audio installation and especially GEM for the actual video processing and movement detection. Allthough it works fine on my development plattform, an old ibook G4, a few differences of the behaviour betweeb Mac and Windows of some GEM objects make me worry.

My development machine (on the go... is an old ibook with tiger (and an ati 9200) and a new pc with xp sp2 and a geforce 7600. The target plattform will likely be a pc also with xp sp2.
The software I use is the pd-extended 0.38-4 release.

My development works as this: I use a movie that is prerecorded and shows movement of a single object (like an elevator moving up and down with stops in between).
My patch is partially build like the GEM documentation example Gem - 04.video - 0.3.movement_detection.pd. Additionally to this I have subpatches that do movement analysis patches for speed and accelleration of a single moving object.

On the mac (with an ATI 9200) the initial view of the prerecorded movie is quite dark and the basic movement detection is very sensible and works quite well (and also the analysis).
On windows (with a geforce 7600) it is different. The movie looks quite normal, with the normal brightness (the mac was very dark), and the movement detection is very insensitive and does not really work.

Things that I recognized and resulting questions:
1. Is there a difference in initial values the GEM objects have if there is no explicit initialisation?

2. The colormodel seems to be different. A color of 1 1 1 is black on the ibook (with the ATI card) and white at the PC (with the geforce)

3. What reason can it have, that the displayed video on the mac (with the given example) is initially way darker than expected.

4. On the mac, the prerecorded movie cycles infinitely with the auto option of pix_film whereas pure on windows stops after one cycle. Is there a reason for this behaviour?

5. Is there actually a difference between the way GEM objects are initialized between Windows and Mac and also between different opengl vendors (like the color model between ati and nvidia).

Hope someone can share some experiences with GEM and how to work around the difficulties of GEM on different plattforms.

Regards,
Michael.

tx Megale for your answer, im under OSX and using Pd-0.39.2-extended-test1.app and that's why i pose the question since in linux i know how to locate the webcam, simply /dev/video0..but under os x im simply lost.. i did search what you said an got some patches to play with and see but so far i get this when trying to load [pix_videoDS]

... couldn't create

If i take away the DS part it comes up

pix_videoDarwin: height 320 width 240
pix_videoDarwin: could not make new SG channnel
pix_videoDarwin: could not set SG ChannelBounds
pix_videoDarwin: could not set SG ChannelUsage
pix_videoDarwin: set SG NormalQuality
pix_videoDarwin: Using YUV

but when trying to access any help file or documentation i get this:

sorry, couldn't find help patch for "Gem/pix_videoDarwin.pd"

what means that so far the learning curve, withouth dokumentantion, gets really steep..

thanks for you answer, it opened a way..but please if possible (if you are under OS X) could you share a llittle example patch?

tx,
/kad

From http://gem.iem.at/manual/ListObjects.html

pix_film - use a movie file as a pix source for image-processing
pix_movie - use a movie file as a pix source and load it immediately into the texture-buffer

I don't use Gem myself, but reading that it seems pix_movie would load the whole video file into RAM, and probably into the video RAM on the graphics card. Not knowing much about Gem, there may be a difference between "pix for image processing" and "pix for texture", which may or may not be important.