I use the following method to get a decompressed uiimage from file system. However the UIImageView is colored as red when I turn on the color blended layer, even though the UIImageView is set to Opaque.
The images on file system don't have alpha channel. I tried set CGContextSetAlpha(bitmapContext, 1), but still has blended layer.
Anyone know how to remove alpha channel when using CGContextDrawImage?
- (UIImage *)decompressedImage
{
CGImageRef imageRef = self.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),
kCGImageAlphaPremultipliedFirst | kCGBitmapByteOrder32Little
);
// kCGImageAlphaPremultipliedFirst | kCGBitmapByteOrder32Little are the bit flags required
// so that the main thread doesn't have any conversions to do.
CGContextDrawImage(bitmapContext, rect, imageRef);
CGImageRef decompressedImageRef = CGBitmapContextCreateImage(bitmapContext);
UIImage* decompressedImage = [UIImage imageWithCGImage:decompressedImageRef
scale:[[UIScreen mainScreen] scale]
orientation:UIImageOrientationUp];
CGImageRelease(decompressedImageRef);
CGContextRelease(bitmapContext);
return decompressedImage;
}
To check if the image has an alpha channel, go to the channel dialog and verify that an entry for “Alpha” exists, besides Red, Green and Blue. If this is not the case, add a new alpha channel from the layers menu; Layer+Transparency → Add Alpha Channel.
Any SwiftUI view can be partially or wholly transparent using the opacity() modifier. This accepts a value between 0 (completely invisible) and 1 (fully opaque), just like the alpha property of UIView in UIKit.
In the options for the context, try the option
kCGImageAlphaNoneSkipLast
or
kCGImageAlphaNoneSkipFirst
Depending on if you are using RGBA or ARGB
ie,
CGContextRef bitmapContext = CGBitmapContextCreate(NULL,
rect.size.width,
rect.size.height,
CGImageGetBitsPerComponent(imageRef),
CGImageGetBytesPerRow(imageRef),
CGImageGetColorSpace(imageRef),
kCGImageAlphaNoneSkipLast | kCGBitmapByteOrder32Little
);
Same result but less code and things to worry about:
func removeAlpha(from inputImage: UIImage) -> UIImage {
let format = UIGraphicsImageRendererFormat.init()
format.opaque = true //Removes Alpha Channel
format.scale = inputImage.scale //Keeps original image scale.
let size = inputImage.size
return UIGraphicsImageRenderer(size: size, format: format).image { _ in
inputImage.draw(in: CGRect(origin: .zero, size: size))
}
}
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