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Editorial Team
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Asked: 2026-05-31T14:26:14+00:00

I am creating tiles for a larger image and I’m saving them to disk.

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I am creating tiles for a larger image and I’m saving them to disk. Question: Is there any way I can optimize the image so that reading and decompressing the PNG from disk is faster? Possibly by changing the order or color bytes in the color space on a custom bitmap context from which the image is saved?

UIImage *fullSizeImage = [self cachedImageWithURL:imageURL];
CGRect tileRect = (CGRect){{column*tileSize.width, row*tileSize.height}, {tileSize.width, tileSize.height}};
CGRect totalRect = (CGRect){CGPointZero, fullSizeImage.size};
tileRect = CGRectIntersection(tileRect, totalRect);
CGImageRef tileImage = CGImageCreateWithImageInRect([fullSizeImage CGImage], tileRect);
UIImage *retImage = [UIImage imageWithCGImage:tileImage];
[self.cache setObject:retImage forKey:cacheURL cost:0];
[retImage savePNGAsyncToURL:cacheURL];
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1 Answer

  1. Editorial Team

    I’ve benchmarked this, and it looks that speed is closely correlated to file size (smaller file is faster):

    http://imageoptim.com/tweetbot.html

    If you’re OK with lossy compression, then use pngquant to create those files. At 8bpp they’ll have 1/4th of data to begin with.

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