How to check if a uiimage is blank? (empty, transparent)

Question

which is the best way to check whether a UIImage is blank?
I have this painting editor which returns a UIImage; I don\'t want to save this imag

Answer 1

I'm not at my Mac, so I can't test this (and there are probably compile errors). But one method might be:

//The pixel format depends on what sort of image you're expecting. If it's RGBA, this should work
typedef struct
{
   uint8_t red;
   uint8_t green;
   uint8_t blue;
   uint8_t alpha;
} MyPixel_T;

UIImage *myImage = [self doTheThingToGetTheImage];
CGImageRef myCGImage = [myImage CGImage];

//Get a bitmap context for the image
CGBitmapContextRef *bitmapContext = 
CGBitmapContextFreate(NULL, CGImageGetWidth(myCGImage), CGImageGetHeight(myCGImage), 
                      CGImageGetBitsPerComponent(myCGImage), CGImageGetBytesPerRow(myCGImage),
                      CGImageGetColorSpace(myCGImage), CGImageGetBitmapInfo(myCGImage));

//Draw the image into the context
CGContextDrawImage(bitmapContext, CGRectMake(0, 0, CGImageGetWidth(myCGImage), CGImageGetHeight(myCGImage)), myCGImage);

//Get pixel data for the image
MyPixel_T *pixels = CGBitmapContextGetData(bitmapContext);
size_t pixelCount = CGImageGetWidth(myCGImage) * CGImageGetHeight(myCGImage);

for(size_t i = 0; i < pixelCount; i++)
{
   MyPixel_T p = pixels[i];
   //Your definition of what's blank may differ from mine
   if(p.red > 0 && p.green > 0 && p.blue > 0 && p.alpha > 0)
      return NO;
}

return YES;