iOS 17 Problems in getting RGB color from image

Question

Created Oct ’23

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I have written and used the code to get the colors from CGImage and it worked fine up to iOS16. However, when I use the same code in iOS17, Red and Blue out of RGB are reversed.

Is this a temporary bug in the OS and will it be fixed in the future? Or has the specification changed and will it remain this way after iOS17?

Here is my code:

let pixelDataByteSize = 4
guard let cfData = image.cgImage?.dataProvider?.data else { return }
let pointer:UnsafePointer = CFDataGetBytePtr(cfData)
let scale = UIScreen.main.nativeScale
let address = ( Int(image.size.width * scale) * Int(image.size.height * scale / 2) + Int(image.size.width * scale / 2) ) * pixelDataByteSize
let r = CGFloat(pointer[address])   / 255
let g = CGFloat(pointer[address+1]) / 255
let b = CGFloat(pointer[address+2]) / 255

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Answer 1

FrankSchlegel OP

Oct ’23

The order of the color channels in a CGImage depends on its alphaInfo and bitmapInfo. The default format for 8-bit images is actually BGRA (instead of RGBA) in many places. Where do you get the image from? What's its bitmapInfo and does it differ between iOS 16 and 17?

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