size of an image

From times to times I have to know the width and height of images. I am using the following code:

UIImage *imageU = [UIImage imageWithContentsOfFile:[[[NSBundle mainBundle] resourcePath] str开发者_运维百科ingByAppendingPathComponent:@"myImage.png"]];

CGFloat imageW = CGImageGetWidth(imageU.CGImage);
CGFloat imageH = CGImageGetHeight(imageU.CGImage);

My question is that if it is there any other way to know the width and height of an image, in pixels, without having to load the image on a variable, that's probably consuming memory. Can the dimensions be read from the file directly without loading the whole image?

This has to work for PNG and JPEG.

thanks.

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You can parse the PNG file which contain the size info in the header. See Get size of image without loading in to memory.

(BTW, you can use imageU.size to get a CGSize of the image.)

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I don't think you can do this "for free", speaking in terms of memory use. You could create an NSInputStream and read/parse the data of the IHDR section (follow @KennyTM's link), then discard everything.