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UIImage+ImmediateLoad.m
Objective-C
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@interface UIImage(ImmediateLoad)
 
+ (UIImage*)imageImmediateLoadWithContentsOfFile:(NSString*)path;
 
@end
 
@implementation UIImage(ImmediateLoad)
 
+ (UIImage*)imageImmediateLoadWithContentsOfFile:(NSString*)path {
UIImage *image = [[UIImage alloc] initWithContentsOfFile:path];
CGImageRef imageRef = [image CGImage];
CGRect rect = CGRectMake(0.f, 0.f, CGImageGetWidth(imageRef), CGImageGetHeight(imageRef));
CGContextRef bitmapContext = CGBitmapContextCreate(NULL,
rect.size.width,
rect.size.height,
CGImageGetBitsPerComponent(imageRef),
CGImageGetBytesPerRow(imageRef),
CGImageGetColorSpace(imageRef),
CGImageGetBitmapInfo(imageRef)
);
CGContextDrawImage(bitmapContext, rect, imageRef);
CGImageRef decompressedImageRef = CGBitmapContextCreateImage(bitmapContext);
UIImage *decompressedImage = [UIImage imageWithCGImage:decompressedImageRef];
CGImageRelease(decompressedImageRef);
CGContextRelease(bitmapContext);
[image release];
return decompressedImage;
}
 
@end

Careful, this doesn't set the best byte ordering. If this is for the screen, you should use CGBitmapContextCreate(imageBuffer, width, height, 8, width*4, colourSpace,
kCGImageAlphaPremultipliedFirst | kCGBitmapByteOrder32Little); instead.

The comment by steipete above is incorrect. The code as written handles this because it is set by the UIImage. If you try the suggested optimization your code will break as soon as you try to render images with monochrome color spaces.

True that, it's a delicate change - but then again, one also can manually set the bits per component and byts per row to not break things.

Hi Steve, I'm pretty sure that the imageRef will also have an internal pointer to the decompressed bits. You could just create a new context with the UIKit functions, draw image then discard the context. The UIImage image would then have an indirect pointer to the decompressed image.

The snippet works on my iphone, but then in the simulator it doesn't work. I get something like : CGBitmapContextCreate: unsupported parameter combination: 8 integer bits/component; 24 bits/pixel; 3-component color space; kCGImageAlphaNone; 1440 bytes/row.

I noticed that for the same troubled image, on the device CGImageGetBytesPerRow(imageRef) == 1920 and width*4 == 1920, but in the simulator CGImageGetBytesPerRow(imageRef) == 1440.

I then tried what steipete suggested and it works on both the device and simulator. Thoughts?

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