UIImage_Category

获取图片上一点的颜色

根据图片上的一点，获得对应的颜色值。

UIImage *image = [UIImage imageNamed:@"sns_icon_15"];UIColor *color = [self getColorAtPoint:CGPointMake(4, 44) atImage:image];

实现代码：

- (UIColor*) getColorAtPoint:(CGPoint)point atImage:(UIImage *)image {    UIColor* color = nil;    CGImageRef cgImage = image.CGImage;    CGContextRef context = [self createARGBBitmapContextFromImage:cgImage];    if (context == NULL) {        return nil;    }    size_t w = CGImageGetWidth(cgImage);    size_t h = CGImageGetHeight(cgImage);    CGRect rect = {{0,0},{w,h}};    CGContextDrawImage(context, rect, cgImage);    unsigned char* data = CGBitmapContextGetData (context);    if (data != NULL) {        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];        color = [UIColor colorWithRed:(red/255.0f) green:(green/255.0f) blue:                 (blue/255.0f) alpha:(alpha/255.0f)];    }    CGContextRelease(context);    if (data) {        free(data);    }    return color;}- (CGContextRef)createARGBBitmapContextFromImage:(CGImageRef)inImage {    CGContextRef context = NULL;    CGColorSpaceRef colorSpace;    void *bitmapData;    int bitmapByteCount;    int bitmapBytesPerRow;    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   = ((int)pixelsWide * 4);    bitmapByteCount     = (bitmapBytesPerRow * (int)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;}

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获得纯色image

• (UIImage )imageWithColor:(UIColor )color size:(CGSize)size {
  CGRect rect = CGRectMake(0.0f, 0.0f, size.width, size.height);
  UIGraphicsBeginImageContext(rect.size);
  CGContextRef context = UIGraphicsGetCurrentContext();

  CGContextSetFillColorWithColor(context, [color CGColor]);
  CGContextFillRect(context, rect);

  UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
  UIGraphicsEndImageContext();

  return image;
  }