Questions tagged [cgcontextdrawimage]

CGContextDrawImage draws an image into a graphics context. It can be used by importing Apple's CoreGraphics framework.

There are some use cases (not the majority) for which the CALayer and Core Animation approach will not work. For those cases, CGContextDrawImage could spend a lot of time in decompressing or resampling the images as necessary because the images will not be cached in the layer tree.

For more information:

• CGContextDrawImage Reference

• Improving Image Drawing Performance on iOS

Example:

Draw your image into a grayscale context

  CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceGray();
  context = CGBitmapContextCreate(nil, inputWidth, inputHeight,
                     8, 0, colorSpace, (CGBitmapInfo)kCGImageAlphaNone);

  CGContextDrawImage(context, imageRect, [imageWithGhost CGImage]);

  CGImageRef imageRef = CGBitmapContextCreateImage(context);
  UIImage * finalImage = [UIImage imageWithCGImage:imageRef];

Related Stack Overflow Questions:

1. CGContextDrawImage draws image upside down when passed UIImage.CGImage

2. CGContextDrawImage is EXTREMELY slow after large UIImage drawn into it

3. rotate image using CGContextDrawImage