JPEG Compression Quality using CGImage

Final Update

After extensive research and following the suggestions in the comments above it appears that there is no way to disable chroma subsampling/decimation with any of Apple’s built-in APIs short of setting kCGImageDestinationLossyCompressionQuality to 1.0 which results in very large images.

If you need to be able to control chroma subsampling/decimation yourself when saving to JPEG then you’ll need to use a 3rd party library such as libjpeg.

Maybe there’s some other API I could use?

WebP is a new image format from Google that gives you better compression than jpg and png, both lossless and lossy. There is a project on github that is pretty easy to use: https://github.com/seanooi/iOS-WebP

You just add a category and the WebP framework to your project to use it.

//Converting To WebP// quality value is [0, 100]NSData *webpData = [UIImage imageToWebP:[UIImage imageNamed:@"image.jpg"] quality:75];//Converting From WebPUIImage *webPImage = [UIImage imageFromWebP:@"/path/to/file"];//Setting image transparency//alpha value is [0, 1]UIImage *transparencyImage = [[UIImage imageNamed:image.jpg] imageByApplyingAlpha:0.5];

The alpha isn't working right, but since you are using jpg, I'm assuming you don't need it.