在.NET组合几个PNG8图像最简单的方法 [英] Easiest way to combine several PNG8 images in .NET

问题描述

我想了一堆8位PNG图像合并成一个更大的PNG图像在C＃。奇怪的是，这似乎是特别困难的。

I'm trying to combine a bunch of 8-bit PNG images into a larger PNG image in C#. Oddly enough, this seems to be particularly difficult.

由于显卡不支持索引颜色，你不能使用，所以我试图建立一个非索引位图（使用图形界面）和转换，为索引颜色的位图。转换是好的，但我想不出如何设置输出图像的调色板。它默认为一些pre定义的调色板里面有什么与我在寻找什么。

Since Graphics does not support indexed color, you can't use that, so I tried building a non-indexed Bitmap (using Graphics) and converting that to indexed color bitmap. The conversion is fine, but I can't figure out how to set the palette of the output image. It defaults to some pre-defined palette which has little to do with what I'm looking for.

所以：

有没有办法来控制位图调色板？还是有另一种方法（System.Windows.Media.Imaging.WriteableBitmap例如），它可以支持呢？

Is there a way to control the bitmap palette? Or is there another method (System.Windows.Media.Imaging.WriteableBitmap, for example) which can support this?

回复：WriteableBitmap的。我似乎无法找到任何的例子网上怎么一会去在这方面相结合的PNG图像，或者即使它使任何意义，尝试它

Re: WriteableBitmap: I can't seem to find any examples online of how one would go about combining PNGs in this context, or even if it makes any sense to attempt it.

推荐答案

事实证明，我能够打造出一个非索引位图和转换使用PngBitmapEn codeR像这样：

It turns out that I was able to build out a non-indexed bitmap and convert using PngBitmapEncoder like so:

    byte[] ConvertTo8bpp(Bitmap sourceBitmap)
    {
        // generate a custom palette for the bitmap (I already had a list of colors
        // from a previous operation
        Dictionary<System.Drawing.Color, byte> colorDict = new Dictionary<System.Drawing.Color, byte>(); // lookup table for conversion to indexed color
        List<System.Windows.Media.Color> colorList = new List<System.Windows.Media.Color>(); // list for palette creation
        byte index = 0;
        unchecked
        {
            foreach (var cc in ColorsFromPreviousOperation)
            {
                colorDict[cc] = index++;
                colorList.Add(cc.ToMediaColor());
            }
        }
        System.Windows.Media.Imaging.BitmapPalette bmpPal = new System.Windows.Media.Imaging.BitmapPalette(colorList);

        // create the byte array of raw image data
        int width = sourceBitmap.Width;
        int height = sourceBitmap.Height;
        int stride = sourceBitmap.Width;
        byte[] imageData = new byte[width * height];

        for (int x = 0; x < width; ++x)
            for (int y = 0; y < height; ++y)
            {
                var pixelColor = sourceBitmap.GetPixel(x, y);
                imageData[x + (stride * y)] = colorDict[pixelColor];
            }

        // generate the image source
        var bsource = BitmapSource.Create(width, height, 96, 96, PixelFormats.Indexed8, bmpPal, imageData, stride);

        // encode the image
        PngBitmapEncoder encoder = new PngBitmapEncoder();
        encoder.Interlace = PngInterlaceOption.Off;
        encoder.Frames.Add(BitmapFrame.Create(bsource));

        MemoryStream outputStream = new MemoryStream();
        encoder.Save(outputStream);

        return outputStream.ToArray();
    }

加辅助扩展方法：

Plus the helper extension method:

    public static System.Windows.Media.Color ToMediaColor(this System.Drawing.Color color)
    {
        return new System.Windows.Media.Color()
        {
            A = color.A,
            R = color.R,
            G = color.G,
            B = color.B
        };
    }

请注意的警惕：在PngBitmapEn codeR实际上似乎减少8 BPP计数到4时，就可以了。当我测试用6种颜色，例如，输出PNG是只有4位。当我使用一个更多彩丰富的图像，这是8位。看起来像一个功能，那么远，虽然这将是很好，如果我有明确的控制权。

Note for the wary: the PngBitmapEncoder actually seems to reduce the bpp count from 8 to 4 when it can. When I test with 6 colors, for example, the output PNG is only 4-bit. When I use a more color-rich image, it's 8-bit. Looks like a feature so far... though it would be nice if I had explicit control over it.

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