UIGraphicsImageRenderer producing Larger file size for Smaller image? - swift

Question

I am resizing an image and in doing so I find that the reduced image produces a larger file than the original. This for the same image.
func imageResizedForSMS() -> UIImage? {
guard let image = self.image else {print("No image to resize");return nil}
let maxDimension:CGFloat = 1280
guard max(image.size.width,image.size.height) > maxDimension else {print("Original image within proper sizing");return image}
let scaleRatio = min(image.size.width,image.size.height) / max(image.size.width,image.size.height)
let scaledTarget = maxDimension * scaleRatio
let targetSize = CGSize(width: image.size.width >= image.size.height ? maxDimension : scaledTarget, height: image.size.height >= image.size.width ? maxDimension : scaledTarget)
let renderer = UIGraphicsImageRenderer(size: targetSize)
let scaledImage = renderer.image { _ in
image.draw(in: CGRect(origin: .zero, size: targetSize))
}
let imageData = scaledImage.jpegData(compressionQuality: 1.0)
let imageSize = imageData?.count ?? 0
print("Size of resized image = \(Double(imageSize) / 1000.0) KB")
let imageData2 = image.jpegData(compressionQuality: 1.0)
let imageSize2 = imageData2?.count ?? 0
print("Size of original image = \(Double(imageSize2) / 1000.0) KB")
return scaledImage
}
The original image dimensions are 4032X3024 and the resized dimensions are 1280X960. However, the resized file size is 11733.6 KB while the original file size is 7088.8 KB
From the debugger log:
Size of resized image = 11733.636 KB
Size of original image = 7088.865 KB
Printing description of image:
<UIImage:0x283978b40 anonymous {4032, 3024} renderingMode=automatic>
Printing description of scaledImage:
<UIImage:0x28394d320 anonymous {1280, 960} renderingMode=automatic>
How is that a reduction in image dimensions is producing a much larger file size?

Answer 1

As usual I figure it out shortly after posting the question no matter how much time was spent prior to posting....
The issue appears to be the display scale. If I set a trait with a displayScale of 1 and then use the code above, the file size is indeed much reduced. It drops from the previous 11733KB to 1474KB which is much smaller than the original of 7088KB
The updated portion of the code above that fixes this issue:
let format = UIGraphicsImageRendererFormat(for: UITraitCollection(displayScale: 1))
let renderer = UIGraphicsImageRenderer(size: targetSize, format: format)
let scaledImage = renderer.image { _ in
image.draw(in: CGRect(origin: .zero, size: targetSize))
}