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How to get pixel information from CIImage of QT frame
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How to get pixel information from CIImage of QT frame



Hi All,

Thanks for your attention to this newbie in CoreImage programming!

I think this must be an old topic since when I met this trouble I found many similar problems on line. However, there are no perfect solution for it, and most importantly, they are not feasible to my situation.

I am now on a video analysis program. We have get the QT movie and show it in a OpenGLView using Core Video(mainly based on the source code of civideoDemo). Now we need to do pixel analysis on the frame of the movie. I am sure that there is no problem on the video->frame since we have done some composite filter based on the CIImage frame we get from the movie.

It is a straight forward idea that we convert each frame into a Core Image object using

[CIImage imageWithCVImageBuffer:currentFrame]

Here currentFrame is defined by:

CVImageBufferRef	currentFrame;

and then our idea is to get the pixel information using NSBitmapImageRep.

One solution of using [[NSBitmapImageRep alloc] initWithCIImage] failed when the program run into a Exec_Bad_Access error.

I tried another way: draw the CIImage on to a CIContext and then render it to bitmap data:

NSData* pixelData = nil;
[ciContextOffScreen render:inputCIImage toBitmap:pixelData rowBytes:rowBytes bounds:[inputCIImage extent] format:kCIFormatRGBAf colorSpace:nil];
if(!pixelData)
[ciContext render:inputCIImage toBitmap:pixelData rowBytes:rowBytes bounds:[inputCIImage extent] format:kCIFormatRGBAf colorSpace:nil];
return [[NSBitmapImageRep alloc] initWithData:pixelData];


But the problem is finally there is no data in pixelData. So finally the returned NSBitmapImageRep is empty.

So I am now stuck here. Any expert who can give me some suggestions?

Thanks for any of your help!

JArod
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