获取图片中某点或区域颜色

- (UIColor *) getPixelColorAtLocation:(CGPoint)point {    UIColor* color = nil;//    NSLog(@"width======%f,height======%f",demoImage.size.width,demoImage.size.height);    CGImageRef inImage = demoImage.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;  }    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.        @try {            int offset = 4*((w*round(point.y))+round(point.x));//            NSLog(@"offset: %d", offset);            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)];        }        @catch (NSException * e) {//            NSLog(@"%@",[e reason]);        }        @finally {        }    }    // When finished, release the context    CGContextRelease(cgctx);    // Free image data memory for the context    if (data) { free(data); }    return color;}//创建取点图片工作域：- (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 );//    NSLog(@"context%@",context);    return context;}

调用方法

[self getPixelColorAtLocation:CGPointMake(x, y)];

原文地址
http://blog.sina.com.cn/s/blog_693de6100101d0ns.html