改变透明图像的图像亮度

Question

我一直在使用我从here找到的代码来改变图像的亮度

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，here是我之前透明的原始图像，here之后。我只想让图像的非透明部分变暗，而不是透明的背景。

Answer 1

当你打电话给Color.FromArgb时你没有提供alpha通道试试这个，看看它是否更好：

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;
}