問題描述

我正在嘗試將圖像保存為單色(黑白，1 位深度)，但我不知道該怎么做.

I am trying to save an image as monochrome (black&white, 1 bit-depth) but I'm coming up lost how to do it.

我從 png 開始并轉(zhuǎn)換為位圖進行打印(它是熱敏打印機，無論如何只支持黑色 - 如果我嘗試將它們作為彩色/灰度發(fā)送，它對于大圖像的速度會很慢).

I am starting with a png and converting to a bitmap for printing (it's a thermal printer and only supports black anyway - plus its slow as hell for large images if I try to send them as color/grayscale).

到目前為止，我的代碼將其轉(zhuǎn)換為位圖非常簡單，但它保留了原始顏色深度.

My code so far is dead simple to convert it to a bitmap, but it is retaining the original colour depth.

Image image = Image.FromFile("C:\test.png");

byte[] bitmapFileData = null;
int bitsPerPixel = 1;
int bitmapDataLength;

using (MemoryStream str = new MemoryStream())
{
    image.Save(str, ImageFormat.Bmp);
    bitmapFileData = str.ToArray();
}

推薦答案

這是我放在一起的一些代碼，它采用全彩色(24 位/像素)圖像，并將其轉(zhuǎn)換為 1 位/像素輸出位圖，應(yīng)用標(biāo)準(zhǔn) RGB 到灰度轉(zhuǎn)換，然后使用 Floyd-Steinberg 將灰度轉(zhuǎn)換為 1 位/像素輸出.

Here's some code I put together that takes a full colour (24 bits/pixel) image, and converts it to a 1 bit/pixel output bitmap, applying a standard RGB to greyscale conversion, and then using Floyd-Steinberg to convert greyscale to the 1 bit/pixel output.

請注意，這絕不應(yīng)該被視為理想"的實現(xiàn)，但它確實有效.如果您愿意，可以應(yīng)用許多改進.例如，它將整個輸入圖像復(fù)制到 data 數(shù)組中，而我們實際上只需要在內(nèi)存中保留兩行(當(dāng)前"和下一個"行)來累積錯誤數(shù)據(jù).盡管如此，性能似乎還可以接受.

Note that this should by no means be considered an "ideal" implementation, but it does work. There are a number of improvements that could be applied if you wanted. For example, it copies the entire input image into the data array, whereas we really only need to keep two lines in memory (the "current" and "next" lines) for accumulating the error data. Despite this, performance seems acceptable.

public static Bitmap ConvertTo1Bit(Bitmap input)
{
    var masks = new byte[] { 0x80, 0x40, 0x20, 0x10, 0x08, 0x04, 0x02, 0x01 };
    var output = new Bitmap(input.Width, input.Height, PixelFormat.Format1bppIndexed);
    var data = new sbyte[input.Width, input.Height];
    var inputData = input.LockBits(new Rectangle(0, 0, input.Width, input.Height), ImageLockMode.ReadOnly, PixelFormat.Format24bppRgb);
    try
    {
        var scanLine = inputData.Scan0;
        var line = new byte[inputData.Stride];
        for (var y = 0; y < inputData.Height; y++, scanLine += inputData.Stride)
        {
            Marshal.Copy(scanLine, line, 0, line.Length);
            for (var x = 0; x < input.Width; x++)
            {
                data[x, y] = (sbyte)(64 * (GetGreyLevel(line[x * 3 + 2], line[x * 3 + 1], line[x * 3 + 0]) - 0.5));
            }
        }
    }
    finally
    {
        input.UnlockBits(inputData);
    }
    var outputData = output.LockBits(new Rectangle(0, 0, output.Width, output.Height), ImageLockMode.WriteOnly, PixelFormat.Format1bppIndexed);
    try
    {
        var scanLine = outputData.Scan0;
        for (var y = 0; y < outputData.Height; y++, scanLine += outputData.Stride)
        {
            var line = new byte[outputData.Stride];
            for (var x = 0; x < input.Width; x++)
            {
                var j = data[x, y] > 0;
                if (j) line[x / 8] |= masks[x % 8];
                var error = (sbyte)(data[x, y] - (j ? 32 : -32));
                if (x < input.Width - 1) data[x + 1, y] += (sbyte)(7 * error / 16);
                if (y < input.Height - 1)
                {
                    if (x > 0) data[x - 1, y + 1] += (sbyte)(3 * error / 16);
                    data[x, y + 1] += (sbyte)(5 * error / 16);
                    if (x < input.Width - 1) data[x + 1, y + 1] += (sbyte)(1 * error / 16);
                }
            }
            Marshal.Copy(line, 0, scanLine, outputData.Stride);
        }
    }
    finally
    {
        output.UnlockBits(outputData);
    }
    return output;
}

public static double GetGreyLevel(byte r, byte g, byte b)
{
    return (r * 0.299 + g * 0.587 + b * 0.114) / 255;
}

這篇關(guān)于將位圖轉(zhuǎn)換為單色的文章就介紹到這了，希望我們推薦的答案對大家有所幫助，也希望大家多多支持html5模板網(wǎng)！