Adding and Saving a Border Around a UIImage with Core Graphics
I recently had to place a border around an image of unknown size and save it back as an image. Here is how:
Start with a UIImage:
Run it through this method:
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| - (UIImage *)addBorderToImage:(UIImage *)image { | |
| CGImageRef bgimage = [image CGImage]; | |
| float width = CGImageGetWidth(bgimage); | |
| float height = CGImageGetHeight(bgimage); | |
| // Create a temporary texture data buffer | |
| void *data = malloc(width * height * 4); | |
| // Draw image to buffer | |
| CGContextRef ctx = CGBitmapContextCreate(data, | |
| width, | |
| height, | |
| 8, | |
| width * 4, | |
| CGImageGetColorSpace(image.CGImage), | |
| kCGImageAlphaPremultipliedLast); | |
| CGContextDrawImage(ctx, CGRectMake(0, 0, (CGFloat)width, (CGFloat)height), bgimage); | |
| //Set the stroke (pen) color | |
| CGContextSetStrokeColorWithColor(ctx, [UIColor greenColor].CGColor); | |
| //Set the width of the pen mark | |
| CGFloat borderWidth = (float)width*0.05; | |
| CGContextSetLineWidth(ctx, borderWidth); | |
| //Start at 0,0 and draw a square | |
| CGContextMoveToPoint(ctx, 0.0, 0.0); | |
| CGContextAddLineToPoint(ctx, 0.0, height); | |
| CGContextAddLineToPoint(ctx, width, height); | |
| CGContextAddLineToPoint(ctx, width, 0.0); | |
| CGContextAddLineToPoint(ctx, 0.0, 0.0); | |
| //Draw it | |
| CGContextStrokePath(ctx); | |
| // write it to a new image | |
| CGImageRef cgimage = CGBitmapContextCreateImage(ctx); | |
| UIImage *newImage = [UIImage imageWithCGImage:cgimage]; | |
| CFRelease(cgimage); | |
| CGContextRelease(ctx); | |
| // auto-released | |
| return newImage; | |
| } |
You will get back a UIImage with a border. Simple.
Obviously, you will need to adjust the border percentage and color for your own application.
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