获取图片的点的RGB

- (UIColor*) getPixelColorAtLocation:(CGPoint)point {UIColor* color = nil;CGImageRef inImage = self.image.CGImage;// Create off screen bitmap context to draw the image into. Format ARGB is 4 bytes for each pixel: Alpa, Red, Green, BlueCGContextRef cgctx = [self createARGBBitmapContextFromImage:inImage];if (cgctx == NULL) { return nil; /* error */ } size_t w = CGImageGetWidth(inImage);size_t h = CGImageGetHeight(inImage);CGRect rect = {{0,0},{w,h}}; // Draw the image to the bitmap context. Once we draw, the memory // allocated for the context for rendering will then contain the // raw image data in the specified color space.CGContextDrawImage(cgctx, rect, inImage); // Now we can get a pointer to the image data associated with the bitmap// context.unsigned char* data = CGBitmapContextGetData (cgctx);if (data != NULL) {//offset locates the pixel in the data from x,y. //4 for 4 bytes of data per pixel, w is width of one row of data.int offset = 4*((w*round(point.y))+round(point.x));int alpha = data[offset]; int red = data[offset+1]; int green = data[offset+2]; int blue = data[offset+3]; NSLog(@"offset: %i colors: RGB A %i %i %i %i",offset,red,green,blue,alpha);color = [UIColor colorWithRed:(red/255.0f) green:(green/255.0f) blue:(blue/255.0f) alpha:(alpha/255.0f)];}// When finished, release the contextCGContextRelease(cgctx); // Free image data memory for the contextif (data) { free(data); }return color;}- (CGContextRef) createARGBBitmapContextFromImage:(CGImageRef) inImage {CGContextRef context = NULL;CGColorSpaceRef colorSpace;void * bitmapData;int bitmapByteCount;int bitmapBytesPerRow;// Get image width, height. We'll use the entire image.size_t pixelsWide = CGImageGetWidth(inImage);size_t pixelsHigh = CGImageGetHeight(inImage);// Declare the number of bytes per row. Each pixel in the bitmap in this// example is represented by 4 bytes; 8 bits each of red, green, blue, and// alpha.bitmapBytesPerRow = (pixelsWide * 4);bitmapByteCount = (bitmapBytesPerRow * pixelsHigh);// Use the generic RGB color space.colorSpace = CGColorSpaceCreateDeviceRGB();if (colorSpace == NULL){fprintf(stderr, "Error allocating color space/n");return NULL;}// Allocate memory for image data. This is the destination in memory// where any drawing to the bitmap context will be rendered.bitmapData = malloc( bitmapByteCount );if (bitmapData == NULL) {fprintf (stderr, "Memory not allocated!");CGColorSpaceRelease( colorSpace );return NULL;}// Create the bitmap context. We want pre-multiplied ARGB, 8-bits // per component. Regardless of what the source image format is // (CMYK, Grayscale, and so on) it will be converted over to the format// specified here by CGBitmapContextCreate.context = CGBitmapContextCreate (bitmapData, pixelsWide, pixelsHigh, 8, // bits per component bitmapBytesPerRow, colorSpace, kCGImageAlphaPremultipliedFirst);if (context == NULL){free (bitmapData);fprintf (stderr, "Context not created!");}// Make sure and release colorspace before returningCGColorSpaceRelease( colorSpace );return context;}