How to get pixel information from CIImage of QT frame
How to get pixel information from CIImage of QT frame
- Subject: How to get pixel information from CIImage of QT frame
- From: JArod Wen <email@hidden>
- Date: Tue, 15 Jan 2008 18:51:23 -0500
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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