ios - 在 CGRect 中查找主色的算法不起作用

Question

我正在尝试编写一种方法，该方法返回 UIView 中某个区域(由 CGRect 表示)内最常见的颜色。

这是我到目前为止开发的代码，但它似乎不起作用。 NSLog 输出列出了每个像素的颜色，它始终显示白色 (255,255,255)，即使我添加了一些红色条纹也是如此。

如果有人能告诉我问题出在哪里，我将不胜感激:

- (UIColor *) dominantColorInRect:(CGRect)rect
{
    UIColor * dominantColor = nil;
    NSMutableDictionary * dictionary = [[NSMutableDictionary alloc] init];

    int bytesPerPixel = 4;
    int bytesPerRow = bytesPerPixel * rect.size.width;
    NSUInteger bitsPerComponent = 8;
    unsigned int bitmapSize = bytesPerRow * rect.size.height;
    unsigned char pixelData[bitmapSize];

    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();

    CGContextRef context = CGBitmapContextCreate(pixelData,
                                                 rect.size.width,
                                                 rect.size.height,
                                                 bitsPerComponent,
                                                 bytesPerRow,
                                                 colorSpace,   
                                                 kCGImageAlphaPremultipliedLast);


    CGContextTranslateCTM(context, -rect.origin.x, -rect.origin.y);
    [self.layer renderInContext:context];

    CGContextRelease(context);
    CGColorSpaceRelease(colorSpace);

    if (pixelData) {
        unsigned long size = sizeof(pixelData)/sizeof(unsigned char);
        for (int i = 0; i < size; i += bytesPerPixel) {
            UIColor * color = [UIColor colorWithRed:pixelData[0]/255.0 
                                       green:pixelData[1]/255.0 
                                       blue:pixelData[2]/255.0 
                                       alpha:pixelData[3]/255.0];

            if (color) {

                const CGFloat * colors = CGColorGetComponents( color.CGColor);
                CGFloat red = colors[0]*255;
                CGFloat green = colors[1]*255;
                CGFloat blue = colors[2]*255;

                NSLog(@"This Color: %f,%f,%f",red,green,blue);


                NSInteger count = [[dictionary objectForKey:color] integerValue];
                count++;
                [dictionary setObject:[NSNumber numberWithInt:count] forKey:color];
            }

        }

    }

    int highestFrequency = 0;
    for (id color in dictionary) {
        NSInteger count = [[dictionary objectForKey:color] integerValue];
        //NSInteger count = [object[1] integerValue];
        if (count > highestFrequency) {
            highestFrequency = count;
            dominantColor = color;
        }
    }

    return dominantColor;
}

Answer 1

你重复读取第一个像素的值

UIColor * color = [UIColor colorWithRed:pixelData[0]/255.0 
                                   green:pixelData[1]/255.0 
                                   blue:pixelData[2]/255.0 
                                   alpha:pixelData[3]/255.0];

我想应该是这样的

UIColor * color = [UIColor colorWithRed:pixelData[i]/255.0 
                                   green:pixelData[i+1]/255.0 
                                   blue:pixelData[i+2]/255.0 
                                   alpha:pixelData[i+3]/255.0];