有没有办法在索引颜色位图（C#）中提取像素的索引？

Question

我已将带有唯一调色板的索引彩色图像 (8bppI) 加载到 C# 程序中，我需要访问该图像中颜色的 索引。但是，唯一的访问函数似乎是返回颜色而不是索引的 Bitmap.GetPixel(x,y)。当相同的颜色被插入到相同格式和调色板的位图中时，颜色信息显然被误解为索引，一切都搞砸了。为了清楚起见，这是代码的简化版本：

    public void CreateTerrainMap() {
        visualization = new Bitmap(width, height, PixelFormat.Format8bppIndexed);
        visualizationLock = new LockBitmap(visualization);
        Lock();

        // "TerrainIndex.bmp" is a 256x256 indexed colour image (8bpp) with a unique palette.
        // Debugging confirms that this image loads with its palette and format intact
        Bitmap terrainColours = new Bitmap("Resources\\TerrainIndex.bmp");
        visualization.Palette = terrainColours.Palette;

        Color c;

        for (int x = 0; x < width; x++) { 
            for (int y = 0; y < height; y++) {
                if (Terrain[x, y] < SeaLevel) {
                    c = Color.FromArgb(15); // Counterintuitively, this actually gives index 15 (represented as (0,0,0,15))
                } else {
                    heatIndex = <some number between 0 and 255>;
                    rainIndex = <some number between 0 and 255>;

                    if (IsCoastal(x, y)) {
                        c = Color.FromArgb(35); // Counterintuitively, this actually gives index 35 (represented as (0,0,0,35))
                    } else {
                        // This returns an argb colour rather than an index...
                        c = terrainColours.GetPixel(rainIndex, heatIndex);
                    }
                }
                // ...and this seemingly decides that the blue value is actually an index and sets the wrong colour entirely
                visualizationLock.SetPixel(x, y, c);
            }
        }
    }

TerrainIndex 如下所示： TerrainIndex.bmp

调色板如下所示：Palette

输出应如下所示：Good

但它看起来像这样：Bad

请注意，海洋（索引 15）和海岸（索引 35）看起来是正确的，但其他所有内容都来自调色板的错误部分。

我找不到任何有关在 C# 中使用索引颜色位图的有用信息。我真的希望有人可以向我解释我可能做错了什么，或者指出我正确的方向。

Answer 1

我根据我的评论创建了一个答案。所以“原生”解决方案是这样的（需要允许不安全的代码）：

Bitmap visualization = new Bitmap(width, height, PixelFormat.Format8bppIndexed);
visualization.Palette = GetVisualizationPalette();
BitmapData visualizationData = visualization.LockBits(new Rectangle(Point.Empty, visualization.Size),
    ImageLockMode.WriteOnly, PixelFormat.Format8bppIndexed);
try
{
    unsafe
    {
        byte* row = (byte*)visualizationData.Scan0;
        for (int y = 0; y < visualizationData.Height; y++)
        {
            for (int x = 0; x < visualizationData.Width; x++)
            {
                // here you set the 8bpp palette index directly
                row[x] = GetHeatIndex(x, y);
            }

            row += visualizationData.Stride;
        }
    }
}
finally
{
    visualization.UnlockBits(visualizationData);
}

或者，您可以使用these 库，然后：

using KGySoft.Drawing;
using KGySoft.Drawing.Imaging;

// ...

Bitmap visualization = new Bitmap(width, height, PixelFormat.Format8bppIndexed);
visualization.Palette = GetVisualizationPalette();
using (IWritableBitmapData visualizationData = visualization.GetWritableBitmapData())
{
    for (int y = 0; y < visualizationData.Height; y++)
    {
        IWritableBitmapDataRow row = visualizationData[y];
        for (int x = 0; x < visualizationData.Width; x++)
        {
            // setting pixel by palette index
            row.SetColorIndex(x, GetHeatIndex(x, y));

            // or: directly by raw data (8bpp means 1 byte per pixel)
            row.WriteRaw<byte>(x, GetHeatIndex(x, y));

            // or: by color (automatically applies the closest palette index)
            row.SetColor(x, GetHeatColor(x, y));
        }
    }
}

编辑： 对于读取像素/索引，您可以使用terrainColors.GetReadableBitmapData()，这样您就可以以非常相似的方式使用rowTerrain.GetColorIndex(x) 或rowTerrain.ReadRaw<byte>(x)。