裁剪/删除图像边缘不需要的空间

Posted 2023-02-25

【中文标题】裁剪/删除图像边缘不需要的空间

【英文标题】：Crop/Remove Unwanted Space at the edges of image

【发布时间】：2012-11-25 06:51:19

【问题描述】：

我进行了很多搜索以删除不需要的空间，但找不到。我只找到了可以用来删除黑白背景空间的链接。但我的背景图像可以是任何东西。所以，如果我有这些图片，

如何提取我需要的图像部分。例如，

【问题讨论】：

首先，我会选择图像角落的颜色，如果它们相同（或至少 3 个），然后迭代像素，将与角落匹配的颜色变黑，美白别人。

你保证有单色/纯色背景吗？背景的总面积是否总是大于包含的图片？边缘是否总是有至少 1 个像素的背景颜色边框？

我坚信这很简单，实现可能会因您使用的库而异。

@Kal_Torak，颜色大多是单一的

你处于什么样的环境中？窗体？ WPF？还有什么？它们是什么样的图像？ PNG？其他格式？

【参考方案1】：

这是我对您问题的解决方案：

我已经声明了一个获取原始图像的方法，然后它通过检查提供的图像的角来查找背景颜色，如果至少 3 个角具有相似的颜色（最多 10% 偏移） 然后我们找到了背景颜色，然后它试图找到图像中那些形状的边界，这些形状的颜色当然与背景颜色不同

在找到边界后，函数裁剪图像并将新的裁剪区域作为新的位图返回！

这是演示文件：Download

完整解决方案：Download

结果如下：

Image 1：

Image 2：

Image 3：

这是ImageProcessingTools 类中的函数 简化，

public class ImageHelper

    #region CropUnwantedBackground
    public static Bitmap CropUnwantedBackground(Bitmap bmp)
    
        var backColor = GetMatchedBackColor(bmp);
        if (backColor.HasValue)
        
            var bounds = GetImageBounds(bmp, backColor);
            var diffX = bounds[1].X - bounds[0].X + 1;
            var diffY = bounds[1].Y - bounds[0].Y + 1;
            var croppedBmp = new Bitmap(diffX, diffY);
            var g = Graphics.FromImage(croppedBmp);
            var destRect = new Rectangle(0, 0, croppedBmp.Width, croppedBmp.Height);
            var srcRect = new Rectangle(bounds[0].X, bounds[0].Y, diffX, diffY);
            g.DrawImage(bmp, destRect, srcRect, GraphicsUnit.Pixel);
            bmp.Dispose();
            return croppedBmp;
        
        else
        
            bmp.Dispose();
            return null;
        
    
    #endregion

    #region Private Methods

    #region GetImageBounds
    private static Point[] GetImageBounds(Bitmap bmp, Color? backColor)
    
        //--------------------------------------------------------------------
        // Finding the Bounds of Crop Area bu using Unsafe Code and Image Proccesing
        Color c;
        int width = bmp.Width, height = bmp.Height;
        bool upperLeftPointFounded = false;
        var bounds = new Point[2];
        for (int y = 0; y < height; y++)
        
            for (int x = 0; x < width; x++)
            
                c = bmp.GetPixel(x, y);
                bool sameAsBackColor = ((c.R <= backColor.Value.R * 1.1 && c.R >= backColor.Value.R * 0.9) &&
                                        (c.G <= backColor.Value.G * 1.1 && c.G >= backColor.Value.G * 0.9) &&
                                        (c.B <= backColor.Value.B * 1.1 && c.B >= backColor.Value.B * 0.9));
                if (!sameAsBackColor)
                
                    if (!upperLeftPointFounded)
                    
                        bounds[0] = new Point(x, y);
                        bounds[1] = new Point(x, y);
                        upperLeftPointFounded = true;
                    
                    else
                    
                        if (x > bounds[1].X)
                            bounds[1].X = x;
                        else if (x < bounds[0].X)
                            bounds[0].X = x;
                        if (y >= bounds[1].Y)
                            bounds[1].Y = y;
                    
                
            
        
        return bounds;
     
    #endregion

    #region GetMatchedBackColor
    private static Color? GetMatchedBackColor(Bitmap bmp)
    
        // Getting The Background Color by checking Corners of Original Image
        var corners = new Point[]
            new Point(0, 0),
            new Point(0, bmp.Height - 1),
            new Point(bmp.Width - 1, 0),
            new Point(bmp.Width - 1, bmp.Height - 1)
        ; // four corners (Top, Left), (Top, Right), (Bottom, Left), (Bottom, Right)
        for (int i = 0; i < 4; i++)
        
            var cornerMatched = 0;
            var backColor = bmp.GetPixel(corners[i].X, corners[i].Y);
            for (int j = 0; j < 4; j++)
            
                var cornerColor = bmp.GetPixel(corners[j].X, corners[j].Y);// Check RGB with some offset
                if ((cornerColor.R <= backColor.R * 1.1 && cornerColor.R >= backColor.R * 0.9) &&
                    (cornerColor.G <= backColor.G * 1.1 && cornerColor.G >= backColor.G * 0.9) &&
                    (cornerColor.B <= backColor.B * 1.1 && cornerColor.B >= backColor.B * 0.9))
                
                    cornerMatched++;
                
            
            if (cornerMatched > 2)
            
                return backColor;
            
        
        return null;
      
    #endregion
    
    #endregion

这是 ASP.NET 中的一个简单用法，

if (IsPostBack && Request.Files.Count > 0)

    var file = Request.Files[0];
    var bmp = new Bitmap(file.InputStream);
    var croppedBmp = ImageHelper.CropUnwantedBackground(bmp);
    Response.ContentType = file.ContentType;
    croppedBmp.Save(Response.OutputStream, ImageFormat.Jpeg);
    Response.End();

最后我要提一下，这些很棒的教程在图像处理方面帮助了我很多：

Image Processing for Dummies with C# and GDI+

Image Processing using C#

希望对你有帮助:)

【讨论】：

@Mehran 提供的链接不起作用。您还有可下载的解决方案吗？

@LP13 幸运的是我找到了解决方案！这是可下载解决方案的链接：dropbox.com/s/wpf78g3lmzq3jg4/Demo.rar?dl=0

【参考方案2】：

这是一种更可靠的方法，它使用 Sobel 能量滤波器和快速边界框检测例程（从 WhitespaceTrimmer plugin 中提取 ImageResizer）。

namespace ImageResizer.Plugins.WhitespaceTrimmer 
public class BoundingBoxFinder 

    /// <summary>
    /// Returns a rectangle inside 'lookInside' that bounds any energy greater than 'threshold'. 
    /// </summary>
    /// <param name="image"></param>
    /// <param name="lookInside">A rectangle of 'image' to look inside. </param>
    /// <param name="threshold">1-255, the energy threshold to detect activity. 80-150 is a good range.</param>
    /// <returns></returns>
    public Rectangle FindBoxSobel(Bitmap originalImage, Rectangle lookInside, byte threshold) 

        Bitmap image = originalImage;
        try 
            //Convert if needed (makes an extra copy)
            if (image.PixelFormat != PixelFormat.Format24bppRgb &&
                image.PixelFormat != PixelFormat.Format32bppArgb &&
                image.PixelFormat != PixelFormat.Format32bppRgb) 
                image = AForge.Imaging.Image.Clone(image, PixelFormat.Format24bppRgb);
            

            //Crop if needed (makes an extra copy unless we converted too, then only 1 extra copy)
            if (!lookInside.Equals(new Rectangle(0, 0, image.Width, image.Height))) 
                Bitmap oldImage = image;
                try 
                    image = new Crop(lookInside).Apply(image);
                 finally 
                    if (oldImage != originalImage) oldImage.Dispose(); //Dispose the cloned 
                
            


            //Makes 1 more copy at 1/3rd the size, in grayscale
            Rectangle result = FindBoxSobel(image, threshold);
            return new Rectangle(lookInside.X + result.X, lookInside.Y + result.Y, result.Width, result.Height);


         finally 
            if (image != originalImage) image.Dispose();
        

    
    /// <summary>
    /// Requires 24 bit or 32 bit (A) RGB image. 
    /// </summary>
    /// <param name="rgb"></param>
    /// <param name="threshold"></param>
    /// <returns></returns>
    public Rectangle FindBoxSobel(Bitmap rgb, byte threshold) 
        using (Bitmap gray = Grayscale.CommonAlgorithms.Y.Apply(rgb)) 

            //Apply sobel operator to grayscale image
            new SobelEdgeDetector().ApplyInPlace(gray);
            //Threshold into black and white.
            new Threshold(threshold).ApplyInPlace(gray);
            //Trim only exact black pixels
            // lock source bitmap data
            BitmapData data = gray.LockBits(new Rectangle(0, 0, gray.Width, gray.Height), ImageLockMode.ReadOnly, gray.PixelFormat);
            try 
                return FindBoxExactGrayscale(data, 0);
             finally 
                gray.UnlockBits(data);
            
        
    
    /// <summary>
    /// Returns a bounding box that only excludes the specified color. 
    /// Only works on 8-bit images.
    /// </summary>
    /// <param name="sourceData"></param>
    /// <param name="colorToRemove">The palette index to remove.</param>
    /// <returns></returns>
    public Rectangle FindBoxExactGrayscale(BitmapData sourceData, byte indexToRemove) 
        if (sourceData.PixelFormat != PixelFormat.Format8bppIndexed) throw new ArgumentOutOfRangeException("FindBoxExact only operates on 8-bit grayscale images");
        // get source image size
        int width = sourceData.Width;
        int height = sourceData.Height;
        int offset = sourceData.Stride - width;

        int minX = width;
        int minY = height;
        int maxX = 0;
        int maxY = 0;

        // find rectangle which contains something except color to remove
        unsafe 
            byte* src = (byte*)sourceData.Scan0;

            for (int y = 0; y < height; y++) 
                if (y > 0) src += offset; //Don't adjust for offset until after first row
                for (int x = 0; x < width; x++) 
                    if (x > 0 || y > 0) src++; //Don't increment until after the first pixel.
                    if (*src != indexToRemove) 
                        if (x < minX)
                            minX = x;
                        if (x > maxX)
                            maxX = x;
                        if (y < minY)
                            minY = y;
                        if (y > maxY)
                            maxY = y;
                    
                
            
        

        // check
        if ((minX == width) && (minY == height) && (maxX == 0) && (maxY == 0)) 
            minX = minY = 0;
        

        return new Rectangle(minX,minY,maxX - minX + 1, maxY - minY + 1);
    

【讨论】：

谢谢。我会检查这个。但我认为对于简单的使用，我应该使用不依赖任何库的 GDI+ 方法。

我想这取决于准确性对您来说是否重要。