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Editorial Team
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Asked: 2026-06-08T10:37:58+00:00

I have a big image which is too big to be loaded into memory

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I have a big image which is too big to be loaded into memory but i am only interested in a sub set of pixels within that big image. Is it possible to decode into memory only this subset of pixels? I know that in Android there is a class in the API to do exactly this called BitmapRegionDecoder are something like that

I found CGDataProviderCreateSequential but it needs the raw pixels in the constructor…

Right now i am doing something like this : 

UIImage* srcImage = ...;
    CFDataRef cgImgDataRef = CGDataProviderCopyData(CGImageGetDataProvider(srcImage.CGImage));//After this call, all pixels are decoded into memory and the app crashes
char* imageData = (char*)CFDataGetBytePtr(cgImgDataRef);
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1 Answer

  1. Editorial Team

    The only possible way this might work is if you create an CGImageSourceCreateWithData() (or URL whatever), then create a CGImageRef using CGImageCreateWithJPEGDataProvider or CGImageCreateWithPNGDataProvider. With that CGImageRef, you could TRY to use CGImageCreateWithImageInRect() and pull a subsection of the big image out.

    If what you are trying to do is tile the image please clarify your question as I would have more information for you then.

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