使用 MaxHeight 和 MaxWidth 约束按比例调整图像大小

Question

使用System.Drawing.Image。

如果图像宽度或高度超过最大值，则需要按比例调整大小。 调整大小后，需要确保宽度和高度都没有超过限制。

宽度和高度将自动调整大小，直到不超过最大值和最小值（可能的最大尺寸）并保持比例。

Answer 1

像这样？

public static void Test()
{
    using (var image = Image.FromFile(@"c:\logo.png"))
    using (var newImage = ScaleImage(image, 300, 400))
    {
        newImage.Save(@"c:\test.png", ImageFormat.Png);
    }
}

public static Image ScaleImage(Image image, int maxWidth, int maxHeight)
{
    var ratioX = (double)maxWidth / image.Width;
    var ratioY = (double)maxHeight / image.Height;
    var ratio = Math.Min(ratioX, ratioY);

    var newWidth = (int)(image.Width * ratio);
    var newHeight = (int)(image.Height * ratio);

    var newImage = new Bitmap(newWidth, newHeight);

    using (var graphics = Graphics.FromImage(newImage))
        graphics.DrawImage(image, 0, 0, newWidth, newHeight);

    return newImage;
}

Answer 2

更长的解决方案，但考虑到以下场景：

1. 图片是否小于边界框？
2. 图像和边界框是正方形的吗？
3. 图像是正方形，边界框不是
4. 图像是否比边界框更宽更高
5. 图像是否比边界框宽

6. 图像是否比边界框高

   private Image ResizePhoto(FileInfo sourceImage, int desiredWidth, int desiredHeight)
   {
       //throw error if bouning box is to small
       if (desiredWidth < 4 || desiredHeight < 4)
           throw new InvalidOperationException("Bounding Box of Resize Photo must be larger than 4X4 pixels.");            
       var original = Bitmap.FromFile(sourceImage.FullName);
   
       //store image widths in variable for easier use
       var oW = (decimal)original.Width;
       var oH = (decimal)original.Height;
       var dW = (decimal)desiredWidth;
       var dH = (decimal)desiredHeight;
   
       //check if image already fits
       if (oW < dW && oH < dH)
           return original; //image fits in bounding box, keep size (center with css) If we made it bigger it would stretch the image resulting in loss of quality.
   
       //check for double squares
       if (oW == oH && dW == dH)
       {
           //image and bounding box are square, no need to calculate aspects, just downsize it with the bounding box
           Bitmap square = new Bitmap(original, (int)dW, (int)dH);
           original.Dispose();
           return square;
       }
   
       //check original image is square
       if (oW == oH)
       {
           //image is square, bounding box isn't.  Get smallest side of bounding box and resize to a square of that center the image vertically and horizontally with Css there will be space on one side.
           int smallSide = (int)Math.Min(dW, dH);
           Bitmap square = new Bitmap(original, smallSide, smallSide);
           original.Dispose();
           return square;
       }
   
       //not dealing with squares, figure out resizing within aspect ratios            
       if (oW > dW && oH > dH) //image is wider and taller than bounding box
       {
           var r = Math.Min(dW, dH) / Math.Min(oW, oH); //two dimensions so figure out which bounding box dimension is the smallest and which original image dimension is the smallest, already know original image is larger than bounding box
           var nH = oH * r; //will downscale the original image by an aspect ratio to fit in the bounding box at the maximum size within aspect ratio.
           var nW = oW * r;
           var resized = new Bitmap(original, (int)nW, (int)nH);
           original.Dispose();
           return resized;
       }
       else
       {
           if (oW > dW) //image is wider than bounding box
           {
               var r = dW / oW; //one dimension (width) so calculate the aspect ratio between the bounding box width and original image width
               var nW = oW * r; //downscale image by r to fit in the bounding box...
               var nH = oH * r;
               var resized = new Bitmap(original, (int)nW, (int)nH);
               original.Dispose();
               return resized;
           }
           else
           {
               //original image is taller than bounding box
               var r = dH / oH;
               var nH = oH * r;
               var nW = oW * r;
               var resized = new Bitmap(original, (int)nW, (int)nH);
               original.Dispose();
               return resized;
           }
       }
   }
   

Answer 3

工作解决方案：

用于调整大小小于 100Kb 的图像

WriteableBitmap bitmap = new WriteableBitmap(140,140);
bitmap.SetSource(dlg.File.OpenRead());
image1.Source = bitmap;

Image img = new Image();
img.Source = bitmap;
WriteableBitmap i;

do
{
    ScaleTransform st = new ScaleTransform();
    st.ScaleX = 0.3;
    st.ScaleY = 0.3;
    i = new WriteableBitmap(img, st);
    img.Source = i;
} while (i.Pixels.Length / 1024 > 100);

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