用MaxHeight和MaxWidth约束按比例调整图像大小

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resize。 resize后，需要确保宽度或高度都不超过限制。

宽度和高度将被resize，直到它不会自动超过最大值和最小值（可能的最大尺寸）并保持比例。

Answer 1

喜欢这个？

 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scheme，但是解决了以下情况：

1. 图像是否比边界框小？
2. 图像和边界框是否正方形？
3. 图像是正方形的而边界框不是
4. 图像比边框更宽更高
5. 图像比边界框宽吗？

6. 图像比边界框高

    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scheme：

resize低于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); 

更多参考http://net4attack.blogspot.com/