C#打印标签后出现像素化问题，求解决方案

打印前标签显示正常，但打印完成后出现像素化现象，需求标签尺寸为100×70mm，相关代码如下：

原打印事件代码 #

private void Doc_PrintPage(object sender, PrintPageEventArgs e)
{
 Bitmap bm = new Bitmap(pictureBox1.Width, pictureBox1.Height, System.Drawing.Imaging.PixelFormat.Format32bppRgb);
 /*
 float tgtWidthMM = 100; 
 float tgtHeightMM = 70;
 float tgtWidthInches = tgtWidthMM / 25.4f;
 float tgtHeightInches = tgtHeightMM / 25.4f;
 float srcWidthPx = bm.Width;
 float srcHeightPx = bm.Height; 
 float dpiX = srcWidthPx / tgtWidthInches;
 float dpiY = srcHeightPx / tgtHeightInches;

 bm.SetResolution(dpiX, dpiY);
 */
 pictureBox1.DrawToBitmap(bm, pictureBox1.ClientRectangle);
 e.Graphics.DrawImage((Image)bm, 0, 0);
 bm.Dispose();
}

原绘制标签代码 #

private void pictureBox1_Paint(object sender, PaintEventArgs e)
{
 using (Font myFont = new Font("Arial", 14))
 {
     BarcodeWriter writer = new BarcodeWriter() { Format = BarcodeFormat.CODE_128 };

     e.Graphics.DrawString("Miłego czytania!", myFont, Brushes.Black, new Point(118, 25));
     e.Graphics.DrawImage(writer.Write(serialNumber), new Point(70, 65));
     e.Graphics.DrawString("text", myFont, Brushes.Black, new Point(70, 175));
 }

 using (Font myFont = new Font("Arial", 9))
 {
     e.Graphics.DrawString("text", myFont, Brushes.Black, new Point(137, 205));
     e.Graphics.DrawString("text", myFont, Brushes.Black, new Point(140, 220));
 }
}

问题原因 #

当前代码直接将pictureBox的屏幕分辨率图像绘制到打印画布上，而打印设备的DPI通常远高于屏幕DPI（比如300DPI），低分辨率图像被拉伸后就会出现像素化。另外注释掉的DPI设置逻辑方向错误，应该基于打印设备的DPI创建足够分辨率的图像，而非用屏幕尺寸反推DPI。

解决方案 #

修改代码，直接基于打印设备DPI创建高分辨率Bitmap，并在该Bitmap上绘制标签内容，确保打印清晰度：

修改后的打印事件代码

private void Doc_PrintPage(object sender, PrintPageEventArgs e)
{
    // 目标标签尺寸（毫米）
    float tgtWidthMM = 100;
    float tgtHeightMM = 70;

    // 转换为英寸（1英寸=25.4毫米）
    float tgtWidthInches = tgtWidthMM / 25.4f;
    float tgtHeightInches = tgtHeightMM / 25.4f;

    // 获取打印设备的DPI
    float printDpiX = e.Graphics.DpiX;
    float printDpiY = e.Graphics.DpiY;

    // 计算Bitmap的像素尺寸（匹配打印DPI）
    int bmWidth = (int)Math.Round(tgtWidthInches * printDpiX);
    int bmHeight = (int)Math.Round(tgtHeightInches * printDpiY);

    // 创建高分辨率Bitmap
    using (Bitmap bm = new Bitmap(bmWidth, bmHeight, System.Drawing.Imaging.PixelFormat.Format32bppRgb))
    {
        bm.SetResolution(printDpiX, printDpiY);
        using (Graphics g = Graphics.FromImage(bm))
        {
            // 绘制标签内容
            DrawLabelContent(g, printDpiX, printDpiY);
        }

        // 将Bitmap按实际尺寸绘制到打印画布，避免拉伸
        e.Graphics.DrawImage(bm, 0, 0, tgtWidthInches, tgtHeightInches);
    }
}

提取的标签内容绘制方法

将原Paint事件的绘制逻辑提取为独立方法，适配打印DPI：

private void DrawLabelContent(Graphics g, float dpiX, float dpiY)
{
    // 屏幕DPI默认96，将原屏幕坐标转换为打印DPI下的坐标
    float scaleX = dpiX / 96f;
    float scaleY = dpiY / 96f;

    // 开启高质量渲染，提升文字和图形清晰度
    g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
    g.TextRenderingHint = System.Drawing.Text.TextRenderingHint.ClearTypeGridFit;

    using (Font myFont = new Font("Arial", 14))
    {
        BarcodeWriter writer = new BarcodeWriter() { Format = BarcodeFormat.CODE_128 };
        Image barcodeImage = writer.Write(serialNumber);

        // 应用坐标缩放
        g.DrawString("Miłego czytania!", myFont, Brushes.Black, new PointF(118 * scaleX, 25 * scaleY));
        g.DrawImage(barcodeImage, new PointF(70 * scaleX, 65 * scaleY));
        g.DrawString("text", myFont, Brushes.Black, new PointF(70 * scaleX, 175 * scaleY));

        barcodeImage.Dispose();
    }

    using (Font myFont = new Font("Arial", 9))
    {
        g.DrawString("text", myFont, Brushes.Black, new PointF(137 * scaleX, 205 * scaleY));
        g.DrawString("text", myFont, Brushes.Black, new PointF(140 * scaleX, 220 * scaleY));
    }
}

修改说明 #

1. 放弃依赖pictureBox的低分辨率图像，直接基于打印设备DPI创建高分辨率Bitmap，从根源解决像素化问题。
2. 提取绘制逻辑到独立方法，既复用代码，又能灵活适配屏幕显示和打印两种场景。
3. 开启高质量渲染设置，优化文字和条形码的打印效果。
4. 通过坐标缩放，确保打印内容的布局和原设计完全一致。

内容的提问来源于stack exchange，提问作者Jacek Szczupak