这个棕褐色调转换算法有什么问题？ [英] What is wrong with this sepia tone conversion algorithm?

问题描述

我似乎有一个乌贼墨色调几乎工作正常。由于某种原因，图像的一部分变成石灰绿色！有谁知道我可能会做错了吗？方法如下。

I seem to have a sepia tone that is almost working properly. For some reason a portion of the image turns out to be lime green! Does anyone know what i might be doing wrong? Method is posted below.

private void SepiaBitmap(Bitmap bmp)
{
    Rectangle rect = new Rectangle(0, 0, bmp.Width, bmp.Height);
    System.Drawing.Imaging.BitmapData bmpData = bmp.LockBits(rect, System.Drawing.Imaging.ImageLockMode.ReadWrite,
        System.Drawing.Imaging.PixelFormat.Format32bppRgb);

    IntPtr ptr = bmpData.Scan0;

    int numPixels = bmpData.Width * bmp.Height;
    int numBytes = numPixels * 4;
    byte[] rgbValues = new byte[numBytes];

    System.Runtime.InteropServices.Marshal.Copy(ptr, rgbValues, 0, numBytes);
    for (int i = 0; i < rgbValues.Length; i += 4)
    {
        rgbValues[i + 2] = (byte)((.393 * rgbValues[i + 2]) + (.769 * rgbValues[i + 1]) + (.189 * (rgbValues[i + 0]))); //red
        rgbValues[i + 1] = (byte)((.349 * rgbValues[i + 2]) + (.686 * rgbValues[i + 1]) + (.168 * (rgbValues[i + 0]))); //green
        rgbValues[i + 0] = (byte)((.272 * rgbValues[i + 2]) + (.534 * rgbValues[i + 1]) + (.131 * (rgbValues[i + 0]))); //blue

        if ((rgbValues[i + 2]) > 255)
        {
            rgbValues[i + 2] = 255; 
        }

        if ((rgbValues[i + 1]) > 255)
        {
            rgbValues[i + 1] = 255;
        }
        if ((rgbValues[i + 0]) > 255)
        {
            rgbValues[i + 0] = 255;
        }
    }

    System.Runtime.InteropServices.Marshal.Copy(rgbValues, 0, ptr, numBytes);
    this.Invalidate();
    bmp.UnlockBits(bmpData);

}

推荐答案

要解决此问题，请按如下所示更改循环：

To fix the issue, change the loop like this:

for (int i = 0; i < rgbValues.Length; i += 4)
{
    int red = rgbValues[i + 2];
    int green = rgbValues[i + 1];
    int blue = rgbValues[i + 0];

    rgbValues[i + 2] = (byte)Math.Min((.393 * red) + (.769 * green) + (.189 * blue), 255.0); // red
    rgbValues[i + 1] = (byte)Math.Min((.349 * red) + (.686 * green) + (.168 * blue), 255.0); // green
    rgbValues[i + 0] = (byte)Math.Min((.272 * red) + (.534 * green) + (.131 * blue), 255.0); // blue
}

在您的计算中会出现算术溢出，错误的颜色。 double 的表达式被显式转换为 byte 之前 ，因此它永远不会大于255.

There are arithmetic overflows occurring in your calculations, that's the reason for the wrong colors. An expression of type double is being explicitly cast to byte before it is compared to 255, therefore it will never be greater than 255.

这篇关于这个棕褐色调转换算法有什么问题？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！