c# - Can't set palette in bitmap

Question

I have been writing a PCX decoder and, so far, the PCX image itself parses fine, but I can't work out how to set the palette of a bitmap.

I have created a bitmap like so:

Bitmap bmp = new Bitmap(width,
                        height,
                        stride2,
                        System.Drawing.Imaging.PixelFormat.Format8bppIndexed,
                        pixels);

But I can't seem to set the palette using the following method:

for (int i = 0; i < 256; i += 3)
{
    Color b = new Color();
    b = Color.FromArgb(palette[i], palette[i + 1], palette[i + 2]);
    bmp.Palette.Entries.SetValue(b, i);
}

In this example, I have read through each byte in the palette of the pcx file and stored them in palette[]. from there, I have used this to set the entries in the palette of the bitmap. How do I set the colours?

Answer 1

This had me confused too. It seems bitmap.Palette returns a clone of the bitmap's palette. Once you've modified your copy, you need to reset the bitmap's pallete by using bitmap.Palette = palette, e.g.

ColorPalette palette = bitmap.Palette;
Color entries = palette.Entries;
....
entries[i] = new Color(...);
....
bitmap.Palette = palette; // The crucial statement

See http://www.charlespetzold.com/pwcs/PaletteChange.html