尝试从 C# WinForms 中的 PictureBox 读取像素颜色

Question

我遇到了一个奇怪的问题，当我尝试遍历 PictureBox 的像素或保存 bmp 时，它只是全黑。

该工具的目的是选择字体、大小和样式，然后循环该字体的 ASCII 字符并在图片框中显示每个字符，并将像素数据转换为 HEX 数组，以便我可以在液晶显示器上使用它们。

该工具的主要部分可以正确循环遍历 ASCII 字符并将它们显示在图片框中，但是在将每个字符绘制到图片框之后，然后我尝试遍历 PictureBox 的像素每个像素都返回为 0,0,0 RGB“黑色”，如果我保存绘制到 PictureBox 的 bmp，那也是全黑，但我可以再次看到在 @987654327 中绘制的那个字符的 bmp 正确@ 然而PictureBox 数据和bmp 数据与我在PictureBox 本身中看到的不匹配，我真的迷失了为什么我无法正确迭代或保存bmp 或PictureBox。

我尝试不使用不理想的async 函数，因为我希望 UI 是免费的，并且我尝试了各种方法来读取像素并保存 bmp，但结果是相同的。我希望询问是否有人知道我为什么会出现这种奇怪的行为以及问题的解决方案。

来自埃德的问候。

    using System;
    using System.Collections.Generic;
    using System.Drawing;
    using System.Drawing.Drawing2D;
    using System.Drawing.Imaging;
    using System.IO;
    using System.Threading;
    using System.Threading.Tasks;
    using System.Windows.Forms;

    namespace generateFonts
    {
        public partial class Form1 : Form
        {
            string font = "";
            float fontSize = 0;
            FontStyle fontStyle = FontStyle.Regular;

            public Form1()
            {
                InitializeComponent();
                comboBox1.SelectedIndex = 0;
                comboBox2.SelectedIndex = 0;
                comboBox3.SelectedIndex = 0;

                font = comboBox1.SelectedItem.ToString();
                fontSize = Convert.ToInt32(comboBox2.SelectedItem);
                fontStyle = FontStyle.Regular;
            }

            private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
            {
                font = comboBox1.SelectedItem.ToString();
            }

            private void comboBox2_SelectedIndexChanged(object sender, EventArgs e)
            {
                fontSize = Convert.ToInt32(comboBox2.SelectedItem);
            }

            private void comboBox3_SelectedIndexChanged(object sender, EventArgs e)
            {
                if (comboBox3.SelectedIndex == 0)
                    fontStyle = FontStyle.Regular;
                else if (comboBox3.SelectedIndex == 1)
                    fontStyle = FontStyle.Italic;
                else if(comboBox3.SelectedIndex == 2)
                    fontStyle = FontStyle.Bold;
            }

            private async void button1_Click(object sender, EventArgs e)
            {
                await Task.Run(() => StartProcess(1));
            }

            private void StartProcess(int runs)
            {
                // Font 
                Font myFont = new Font(font, fontSize, fontStyle);

                List<string> bytes = new List<string>();

                string[] bits = { "0", "0", "0", "0", "0", "0", "0", "0" };
                byte bitPos = 0;

                for (byte i = 32; i < 126; i++)
                {
                    //Create a Image-Object on which we can paint
                    Image bmp = new Bitmap(200, 200);

                    //Create the Graphics-Object to paint on the Bitmap
                    Graphics g = Graphics.FromImage(bmp);

                    string c = Convert.ToChar(i).ToString();

                    //Get the perfect Image-Size so that Image-Size = String-Size
                    SizeF size = g.MeasureString(c, myFont);

                    //Use this to become better Text-Quality on Bitmap.
                    g.TextRenderingHint = System.Drawing.Text.TextRenderingHint.AntiAlias;
                    g.InterpolationMode = InterpolationMode.HighQualityBicubic;
                    g.PixelOffsetMode = PixelOffsetMode.HighQuality;

                    //Here we draw the string on the Bitmap
                    g.DrawString(c, myFont, new SolidBrush(Color.Black), 0, 0);

                    if (!Directory.Exists("FontBmps"))
                        Directory.CreateDirectory("FontBmps");

                    this.Invoke((MethodInvoker)delegate ()
                    {
                        pictureBox2.Width = Convert.ToInt32(size.Width);
                        pictureBox2.Height = Convert.ToInt32(size.Height);
                        pictureBox2.Image = bmp; // <--- this is working and the picturebox shows the bmp correctly
                        bmp.Save("FontBmps/" + i + "_" + font + "_" + fontSize + "px_" + fontStyle + ".bmp", ImageFormat.Bmp); // <--- error here: this saves a black square instead of the bmp i see displayed in the picturebox GUI ??
                        // Even if i save the picturebox itself that too is just a black square instead of the correct image shown in the GUI ??

                        // now convert the bmp to a HEX array of pixels
                        for (int h = 0; h < pictureBox2.Height; h++)
                        {
                            for (int w = 0; w < pictureBox2.Width; w++)
                            {
                                Color colour = (pictureBox2.Image as Bitmap).GetPixel(w, h);

                                if (colour.R == 0 && colour.G == 0 && colour.B == 0)
                                {
                                    bits[bitPos] = "1";
                                }
                                else
                                {
                                    bits[bitPos] = "0"; // <-- never hits me, again for some reason the bmp or picturebox is all black pixels data but i see it correctly show in the picturebox GUI ??
                                }

                                if (bitPos < 7)
                                    bitPos++;
                                else
                                {
                                    //string bitStr = bits.ToString();
                                    //string hex = Convert.ToByte(bitStr, 2).ToString("x2");
                                    //bytes.Add(hex);
                                    bitPos = 0;
                                    for(byte n = 0; n < 8; n++)
                                    {
                                        bits[n] = "0";
                                    }
                                }

                            }
                        }

                        if (bitPos != 0)
                        {
                            // TO DO...
                        }

                    });
                    Thread.Sleep(500); // <--- i have this just to see it displaying the chars but i have removed it with no effect to the issue 
                }
                // now add List to a file in the correct format
                foreach (string str in bytes)
                {
                    Console.WriteLine(str);
                    // TO DO...
                }
            }


        }
    }

Answer 1

我相信图像是黑色的，但有些部分是透明的。也就是说，您需要检查 Alpha (Color.A)。您在图片框中看到的是透明的图片框的背景颜色。

鉴于ImageFormat.Bmp 不支持透明度，您不会在保存的文件中看到透明度。请改用Png，它支持透明度（并且具有无损压缩）。

或者，您可以使用Graphics.Clear 将图像设置为您想要的背景颜色（我猜是白色），然后再绘制它。

---

除此之外，我建议使用bmp 而不是(pictureBox2.Image as Bitmap)，并使用Bitmap.LockBits。这将提高性能。

这可能对参考有用：Converting a bitmap to monochrome。另见C# - Faster Alternatives to SetPixel and GetPixel for Bitmaps for Windows Forms App。