ios - UIImage 和寻找中心像素的平均 UIColor

Question

我正在尝试获取 UIImage 中心 16 个像素的平均 UIColor，但是生成的颜色永远不会接近正确。我在这里做错了什么？点参数是正确的，我已经验证过了。我还有另一种方法，它使用同样的点返回中心像素的 UIColor，效果很好。

+ (UIColor*)getAverageColorForImage:(UIImage *)image atLocation:(CGPoint)point
{
    int radialSize = 2;

    int xStartPoint = point.x - radialSize;
    int yStartPoint = point.y - radialSize;
    int xEndPoint = point.x + radialSize;
    int yEndPoint = point.y + radialSize;

    CGImageRef rawImageRef = [image CGImage];

    CFDataRef data = CGDataProviderCopyData(CGImageGetDataProvider(rawImageRef));
    const UInt8 *rawPixelData = CFDataGetBytePtr(data);

    NSUInteger bytesPerRow = CGImageGetBytesPerRow(rawImageRef);
    NSUInteger stride = CGImageGetBitsPerPixel(rawImageRef) / 8;

    unsigned int red   = 0;
    unsigned int green = 0;
    unsigned int blue  = 0;

    for(int row = yStartPoint; row < yEndPoint; row++)
    {
        const UInt8 *rowPtr = rawPixelData + bytesPerRow * row;

        for(int column = xStartPoint; column < xEndPoint; column++)
        {
            red    += rowPtr[0];
            green  += rowPtr[1];
            blue   += rowPtr[2];

            rowPtr += stride;
        }
     }

    CFRelease(data);

    CGFloat f = 1.0f / (255.0f * (yEndPoint - yStartPoint) * (xEndPoint - xStartPoint));
    return [UIColor colorWithRed:f * red  green:f * green blue:f * blue alpha:1.0f];
}

Answer 1

您只是迭代从 startPoint 到 endPoint 的像素。也许使用

for(int row = yStartPoint; row <= yEndPoint; row++)
// ...
for(int column = xStartPoint; column <= xEndPoint; column++)

会修好吗？

此外，您还必须调整您的 rowPtr 以从您的 xStartPoint 开始:

const UInt8 *rowPtr = rawPixelData + bytesPerRow * row + stride * xStartPoint;

否则你将从每行 x = 0 开始。

你的平均值应该这样计算:

int numberOfPixels = (yEndPoint - yStartPoint) * (xEndPoint - xStartPoint);

red /= numberOfPixels;
green /= numberOfPixels;
blue /= numberOfPixels;

return [UIColor colorWithRed:red / 255.0  green:green / 255.0 blue:blue / 255.0 alpha:1.0f];