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POIssue Creating and Masking a Solid Color CGImage
 

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  1. POIssue Creating and Masking a Solid Color CGImage
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    <p>In an iPhone app I have a set of black and white images. I need a function which changes the white areas of the image to transparent and the black to an arbitrary color.</p> <p>I'm trying to create a solid color (black or white) CGImageRef and then masking it with my original image. It's almost working, but the areas which should be transparent are about 1% transparent.</p> <p>Here is the function I have. It accepts a boolean to determine whether the solid color should be black or white.</p> <pre> - (UIImage*) imageWithMask:(UIImage *) maskImage andIsWhite:(BOOL) isWhite { CGImageRef maskImageRef = [maskImage CGImage]; CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB(); CGContextRef context = CGBitmapContextCreate(NULL, maskImage.size.width, maskImage.size.width, 8, 0, colorSpace, kCGImageAlphaPremultipliedLast); if (isWhite) { CGContextSetRGBFillColor(context, (CGFloat)1.0, (CGFloat)1.0, (CGFloat)1.0, (CGFloat)1.0 ); } else { CGContextSetRGBFillColor(context, (CGFloat)0.0, (CGFloat)0.0, (CGFloat)0.0, (CGFloat)1.0 ); } CGContextAddRect(context, CGRectMake(0, 0, maskImage.size.width, maskImage.size.height)); CGContextFillRect(context, CGRectMake(0, 0, maskImage.size.width, maskImage.size.height)); CGImageRef solidImage = CGBitmapContextCreateImage(context); CGColorSpaceRelease(colorSpace); CGContextRelease(context); CGImageRef mask = CGImageMaskCreate(CGImageGetWidth(maskImageRef), CGImageGetHeight(maskImageRef), CGImageGetBitsPerComponent(maskImageRef), CGImageGetBitsPerPixel(maskImageRef), CGImageGetBytesPerRow(maskImageRef), CGImageGetDataProvider(maskImageRef), NULL, false); CGImageRef masked = CGImageCreateWithMask(solidImage, mask); UIImage *maskedUIImage = [UIImage imageWithCGImage:masked]; CGImageRelease(masked); return maskedUIImage; } </pre> <p>Any suggestions are appreciated.</p>
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