Creating a mask from a graphics context
- by Magic Bullet Dave
I want to be able to create a greyscale image with no alpha from a png in the app bundle.
This works, and I get an image created:
// Create graphics context the size of the overlapping rectangle
UIGraphicsBeginImageContext(rectangleOfOverlap.size);
CGContextRef ctx = UIGraphicsGetCurrentContext();
// More stuff
CGContextDrawImage(ctx, drawRect2, [UIImage imageNamed:@"Image 01.png"].CGImage);
// Create the new UIImage from the context
UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
However the resulting image is 32 bits per pixel and has an alpha channel, so when I use CGCreateImageWithMask it doesn't work. I've tried creating a bitmap context thus:
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceGray();
CGContextRef ctx =CGBitmapContextCreate(nil, rectangleOfOverlap.size.width, rectangleOfOverlap.size.height, 8, rectangleOfOverlap.size.width , colorSpace, kCGImageAlphaNone);
UIGraphicsGetImageFromCurrentImageContext returns zero and the resulting image is not created. Am I doing something dumb here?
Any help would be greatly appreciated.
Regards
Dave
