UIImage图片grey处理

- (UIImage *) convertToGreyscale:(UIImage *)i { int kRed = 1; int kGreen = 2; int kBlue = 4; int colors = kGreen; int m_width = i.size.width; int m_height = i.size.height; uint32_t *rgbImage = (uint32_t *) malloc(m_width * m_height * sizeof(uint32_t)); CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB(); CGContextRef context = CGBitmapContextCreate(rgbImage, m_width, m_height, 8, m_width * 4, colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaNoneSkipLast); CGContextSetInterpolationQuality(context, kCGInterpolationHigh); CGContextSetShouldAntialias(context, NO); CGContextDrawImage(context, CGRectMake(0, 0, m_width, m_height), [i CGImage]); CGContextRelease(context); CGColorSpaceRelease(colorSpace); // now convert to grayscale uint8_t *m_imageData = (uint8_t *) malloc(m_width * m_height); for(int y = 0; y < m_height; y++) { for(int x = 0; x < m_width; x++) { uint32_t rgbPixel=rgbImage[y*m_width+x]; uint32_t sum=0,count=0; if (colors & kRed) {sum += (rgbPixel>>24)&255; count++;} if (colors & kGreen) {sum += (rgbPixel>>16)&255; count++;} if (colors & kBlue) {sum += (rgbPixel>>8)&255; count++;} m_imageData[y*m_width+x]=sum/count; } } free(rgbImage); // convert from a gray scale image back into a UIImage uint8_t *result = (uint8_t *) calloc(m_width * m_height *sizeof(uint32_t), 1); // process the image back to rgb for(int i = 0; i < m_height * m_width; i++) { result[i*4]=0; int val=m_imageData[i]; result[i*4+1]=val; result[i*4+2]=val; result[i*4+3]=val; } // create a UIImage colorSpace = CGColorSpaceCreateDeviceRGB(); context = CGBitmapContextCreate(result, m_width, m_height, 8, m_width * sizeof(uint32_t), colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaNoneSkipLast); CGImageRef image = CGBitmapContextCreateImage(context); CGContextRelease(context); CGColorSpaceRelease(colorSpace); UIImage *resultUIImage = [UIImage imageWithCGImage:image]; CGImageRelease(image); // make sure the data will be released by giving it to an autoreleased NSData [NSData dataWithBytesNoCopy:result length:m_width * m_height]; return resultUIImage; }

网上看到的，特意留下