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I have a block of raw pixels of data in the form of RGBA (not preMultipliedAlpha). I want to create a UIImage of that data, retaining the Alpha Channel data.
The best method I have found is to pass it through a CGImage. When I do, the CGImage has no Alpha Channel, so therefore when converted to UIImage I am without one as well.
The question is "How does one make a CGImage that contains an Alpha channel?"
//...
GLubyte *buffer = (GLubyte *) malloc(64 * 64 * 4); // buffer contains unsigned bytes 64 X 64 X 4 bytes per pixel
//...
// make data provider from buffer CGDataProviderRef provider = CGDataProviderCreateWithData(NULL, buffer, (64 * 64 * 4), NULL);
// set up for CGImage creation int bitsPerComponent = 8; int bitsPerPixel = 32; int bytesPerRow = 4 * width; CGColorSpaceRef colorSpaceRef = CGColorSpaceCreateDeviceRGB(); CGBitmapInfo bitmapInfo = kCGBitmapByteOrderDefault CGColorRenderingIntent renderingIntent = kCGRenderingIntentDefault; CGImageRef imageRef = CGImageCreate(width, height, bitsPerComponent, bitsPerPixel, bytesPerRow, colorSpaceRef, bitmapInfo, provider, NULL, NO, renderingIntent);
// test for alpha info = CGImageGetAlphaInfo(imageRef); // Note: Returns “kCGImageAlphaNone”
// make UIImage from CGImage UIImage *newUIImage = [UIImage imageWithCGImage:imageRef];
I have a block of raw pixels of data in the form of RGBA (not preMultipliedAlpha). I want to create a UIImage of that data, retaining the Alpha Channel data.
The best method I have found is to pass it through a CGImage. When I do, the CGImage has no Alpha Channel, so therefore when converted to UIImage I am without one as well.
The question is "How does one make a CGImage that contains an Alpha channel?"
//...
GLubyte *buffer = (GLubyte *) malloc(64 * 64 * 4); // buffer contains unsigned bytes 64 X 64 X 4 bytes per pixel
//...
// make data provider from buffer CGDataProviderRef provider = CGDataProviderCreateWithData(NULL, buffer, (64 * 64 * 4), NULL);
// set up for CGImage creation int bitsPerComponent = 8; int bitsPerPixel = 32; int bytesPerRow = 4 * width; CGColorSpaceRef colorSpaceRef = CGColorSpaceCreateDeviceRGB(); CGBitmapInfo bitmapInfo = kCGBitmapByteOrderDefault CGColorRenderingIntent renderingIntent = kCGRenderingIntentDefault; CGImageRef imageRef = CGImageCreate(width, height, bitsPerComponent, bitsPerPixel, bytesPerRow, colorSpaceRef, bitmapInfo, provider, NULL, NO, renderingIntent);
// test for alpha info = CGImageGetAlphaInfo(imageRef); // Note: Returns kCGImageAlphaNone
// make UIImage from CGImage UIImage *newUIImage = [UIImage imageWithCGImage:imageRef];
Pitfall
Posts: 7New Users
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CGBitmapInfo bitmapInfo = kCGBitmapByteOrderDefault
Can be set up to define how Alpha is dealt with:
CGBitmapInfo bitmapInfo =
kCGBitmapByteOrderDefault | kCGImageAlphaLast;
Sets it up for RGBA, non-pre-multiplied.
Hopefully this will help someone else...
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