IOS获取图片中某个像素点的像素值，包括ARGB的各个值

- (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, Blue        CGContextRef 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 context        CGContextRelease(cgctx);         // Free image data memory for the context        if (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 returning        CGColorSpaceRelease( colorSpace );                return context;}