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Asked: 2026-05-11T10:45:40+00:00

I try to get rounded corners on a UIImage, what I read so far,

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I try to get rounded corners on a UIImage, what I read so far, the easiest way is to use a mask images. For this I used code from TheElements iPhone Example and some image resize code I found. My problem is that resizedImage is always nil and I don’t find the error…

- (UIImage *)imageByScalingProportionallyToSize:(CGSize)targetSize {     CGSize imageSize = [self size];     float width = imageSize.width;     float height = imageSize.height;      // scaleFactor will be the fraction that we'll     // use to adjust the size. For example, if we shrink     // an image by half, scaleFactor will be 0.5. the     // scaledWidth and scaledHeight will be the original,     // multiplied by the scaleFactor.     //     // IMPORTANT: the 'targetHeight' is the size of the space     // we're drawing into. The 'scaledHeight' is the height that     // the image actually is drawn at, once we take into     // account the ideal of maintaining proportions      float scaleFactor = 0.0;      float scaledWidth = targetSize.width;     float scaledHeight = targetSize.height;      CGPoint thumbnailPoint = CGPointMake(0,0);      // since not all images are square, we want to scale     // proportionately. To do this, we find the longest     // edge and use that as a guide.      if ( CGSizeEqualToSize(imageSize, targetSize) == NO )     {          // use the longeset edge as a guide. if the         // image is wider than tall, we'll figure out         // the scale factor by dividing it by the         // intended width. Otherwise, we'll use the         // height.          float widthFactor = targetSize.width / width;         float heightFactor = targetSize.height / height;          if ( widthFactor < heightFactor )             scaleFactor = widthFactor;         else             scaleFactor = heightFactor;          // ex: 500 * 0.5 = 250 (newWidth)          scaledWidth = width * scaleFactor;         scaledHeight = height * scaleFactor;          // center the thumbnail in the frame. if         // wider than tall, we need to adjust the         // vertical drawing point (y axis)          if ( widthFactor < heightFactor )             thumbnailPoint.y = (targetSize.height - scaledHeight) * 0.5;          else if ( widthFactor > heightFactor )             thumbnailPoint.x = (targetSize.width - scaledWidth) * 0.5;     }       CGContextRef mainViewContentContext;     CGColorSpaceRef colorSpace;      colorSpace = CGColorSpaceCreateDeviceRGB();      // create a bitmap graphics context the size of the image     mainViewContentContext = CGBitmapContextCreate (NULL, targetSize.width, targetSize.height, 8, 0, colorSpace, kCGImageAlphaPremultipliedLast);      // free the rgb colorspace     CGColorSpaceRelease(colorSpace);          if (mainViewContentContext==NULL)         return NULL;      //CGContextSetFillColorWithColor(mainViewContentContext, [[UIColor whiteColor] CGColor]);     //CGContextFillRect(mainViewContentContext, CGRectMake(0, 0, targetSize.width, targetSize.height));      CGContextDrawImage(mainViewContentContext, CGRectMake(thumbnailPoint.x, thumbnailPoint.y, scaledWidth, scaledHeight), self.CGImage);      // Create CGImageRef of the main view bitmap content, and then     // release that bitmap context     CGImageRef mainViewContentBitmapContext = CGBitmapContextCreateImage(mainViewContentContext);     CGContextRelease(mainViewContentContext);      CGImageRef maskImage = [[UIImage imageNamed:@'Mask.png'] CGImage];      CGImageRef resizedImage = CGImageCreateWithMask(mainViewContentBitmapContext, maskImage);     CGImageRelease(mainViewContentBitmapContext);      // convert the finished resized image to a UIImage      UIImage *theImage = [UIImage imageWithCGImage:resizedImage];      // image is retained by the property setting above, so we can      // release the original     CGImageRelease(resizedImage);      // return the image     return theImage; }
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  1. The problem was the use of CGImageCreateWithMask which returned an all black image. The solution I found was to use CGContextClipToMask instead:

    CGContextRef mainViewContentContext; CGColorSpaceRef colorSpace;  colorSpace = CGColorSpaceCreateDeviceRGB();  // create a bitmap graphics context the size of the image mainViewContentContext = CGBitmapContextCreate (NULL, targetSize.width, targetSize.height, 8, 0, colorSpace, kCGImageAlphaPremultipliedLast);  // free the rgb colorspace CGColorSpaceRelease(colorSpace);      if (mainViewContentContext==NULL)     return NULL;  CGImageRef maskImage = [[UIImage imageNamed:@'mask.png'] CGImage]; CGContextClipToMask(mainViewContentContext, CGRectMake(0, 0, targetSize.width, targetSize.height), maskImage); CGContextDrawImage(mainViewContentContext, CGRectMake(thumbnailPoint.x, thumbnailPoint.y, scaledWidth, scaledHeight), self.CGImage);   // Create CGImageRef of the main view bitmap content, and then // release that bitmap context CGImageRef mainViewContentBitmapContext = CGBitmapContextCreateImage(mainViewContentContext); CGContextRelease(mainViewContentContext);  // convert the finished resized image to a UIImage  UIImage *theImage = [UIImage imageWithCGImage:mainViewContentBitmapContext]; // image is retained by the property setting above, so we can  // release the original CGImageRelease(mainViewContentBitmapContext);  // return the image return theImage;
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