更改透明图像的图像亮度

Question

我一直在使用从这里找到的这段代码来更改图像的亮度

public Bitmap SetBrightness(Bitmap bmap, int brightness)
    {
        if (brightness < -255) brightness = -255;
        if (brightness > 255) brightness = 255;
        Color c;
        for (int i = 0; i < bmap.Width; i++)
        {
            for (int j = 0; j < bmap.Height; j++)
            {
                c = bmap.GetPixel(i, j);
                int cR = c.R + brightness;
                int cG = c.G + brightness;
                int cB = c.B + brightness;
                if (cR < 0) cR = 1;
                if (cR > 255) cR = 255;
                if (cG < 0) cG = 1;
                if (cG > 255) cG = 255;
                if (cB < 0) cB = 1;
                if (cB > 255) cB = 255;
                bmap.SetPixel(i, j, Color.FromArgb((byte)cR, (byte)cG, (byte)cB));
            }
        }
        return bmap;
    }

它适用于非透明图像，但是当尝试将其应用于透明图像时，它也会填充透明部分。例如，这是我的原始图像，之前是透明度，这里是之后。我只想使图像的非透明部分变暗，而不是透明背景。

Answer 1

当您调用Color.FromArgb时，您不提供 alpha 通道请尝试以下操作，看看它是否效果更好：

public Bitmap SetBrightness(Bitmap bmap, int brightness)
{
    if (brightness < -255) brightness = -255;
    if (brightness > 255) brightness = 255;
    Color c;
    for (int i = 0; i < bmap.Width; i++)
    {
        for (int j = 0; j < bmap.Height; j++)
        {
            c = bmap.GetPixel(i, j);
            int cR = c.R + brightness;
            int cG = c.G + brightness;
            int cB = c.B + brightness;
            if (cR < 0) cR = 1;
            if (cR > 255) cR = 255;
            if (cG < 0) cG = 1;
            if (cG > 255) cG = 255;
            if (cB < 0) cB = 1;
            if (cB > 255) cB = 255;
            bmap.SetPixel(i, j, Color.FromArgb(c.A, (byte)cR, (byte)cG, (byte)cB));
        }
    }
    return bmap;
}