C#从中心裁剪图像

Question

我正在使用.NET(4.5)MVC(4.0)C#(5.0)开发应用程序.我想从我已经拥有的图像生成图像缩略图.现在的要求是它应该从图像中心生成最大方形部分的缩略图而不拉伸除了图像之外的整个图像是方形尺寸.

根据示例我的原始图像大小:578x700我想生成占位符大小的缩略图:200x150,185x138,140x140,89x66,80x80,45x45,28x28

我创建了我的下面的代码,但没有得到确切的结果.这是我生成缩略图的核心方法

    public string GenerateThumbnailFromImage(string imageFilePath, int thumbWidth, int thumbHeight)
    {
        try
        {
            //Check if file exist
            if (File.Exists(imageFilePath))
            {
                //bool preserveAspectRatio = true;
                string oldFilePath = imageFilePath;
                string folderPath = Path.GetDirectoryName(imageFilePath);
                string filename = Path.GetFileNameWithoutExtension(imageFilePath);

                //Rename file with thumbnail size
                filename = filename + "_" + thumbWidth.ToString() + Path.GetExtension(imageFilePath);
                imageFilePath = Path.Combine(folderPath, filename);


                using (Image image = Image.FromFile(oldFilePath))
                {
                    decimal originalWidth = image.Width;
                    decimal originalHeight = image.Height;
                    decimal requiredThumbWidth = thumbWidth;
                    decimal requiredThumbHeight = thumbHeight;
                    decimal startXPosition = 0;
                    decimal startYPosition = 0;
                    decimal screenWidth = originalWidth;
                    decimal screenHeight = originalHeight;
                    decimal ar = thumbWidth < thumbHeight 
                                     ? originalWidth / originalHeight
                                     : originalHeight / originalWidth;

                    //Define Starting Position for thumbnail generation
                    if (originalWidth > originalHeight)
                        startXPosition = (originalWidth - originalHeight) / 2;
                    else if (originalHeight > originalWidth)
                        startYPosition = (originalHeight - originalWidth) / 2;

                    if (thumbWidth>thumbHeight)
                    {
                        requiredThumbWidth = thumbWidth;
                        requiredThumbHeight = requiredThumbWidth*ar;
                    }
                    else if (thumbHeight>thumbWidth)
                    {
                        requiredThumbHeight = thumbHeight;
                        requiredThumbWidth = requiredThumbHeight*ar;
                    }
                    else
                    {
                        requiredThumbWidth = thumbWidth;
                        requiredThumbHeight = thumbWidth;
                    }

                    using (var bmp = new Bitmap((int)requiredThumbWidth, (int)requiredThumbHeight))
                    {
                        Graphics gr = Graphics.FromImage(bmp);
                        gr.SmoothingMode = SmoothingMode.HighQuality;
                        gr.CompositingQuality = CompositingQuality.HighQuality;
                        gr.InterpolationMode = InterpolationMode.High;
                        var rectDestination = new Rectangle(0, 0, (int)requiredThumbWidth, (int)requiredThumbHeight);

                        gr.DrawImage(image, rectDestination, (int)startXPosition, (int)startYPosition, (int)screenWidth, (int)screenHeight, GraphicsUnit.Pixel);
                        bmp.Save(imageFilePath);

                        return filename;
                    }
                }
            }
            return null;
        }
        catch (Exception ex)
        {
            GlobalUtil.HandleAndLogException(ex, this);
            throw ex;
        }
        finally
        {

        }
    }

Answer 1

试试这个:

bool SaveCroppedImage(Image image, int targetWidth, int targetHeight, string filePath)
{
    ImageCodecInfo jpgInfo = ImageCodecInfo.GetImageEncoders().Where(codecInfo => codecInfo.MimeType == "image/jpeg").First();
    Image finalImage = image;
    System.Drawing.Bitmap bitmap = null;
    try
    {
        int left = 0;
        int top = 0;
        int srcWidth = targetWidth;
        int srcHeight = targetHeight;
        bitmap = new System.Drawing.Bitmap(targetWidth, targetHeight);
        double croppedHeightToWidth = (double)targetHeight / targetWidth;
        double croppedWidthToHeight = (double)targetWidth / targetHeight;

        if (image.Width > image.Height)
        {
            srcWidth = (int)(Math.Round(image.Height * croppedWidthToHeight));
            if (srcWidth < image.Width)
            {
                srcHeight = image.Height;
                left = (image.Width - srcWidth) / 2;
            }
            else
            {
                srcHeight = (int)Math.Round(image.Height * ((double)image.Width / srcWidth));
                srcWidth = image.Width;
                top = (image.Height - srcHeight) / 2;
            }
        }
        else
        {
            srcHeight = (int)(Math.Round(image.Width * croppedHeightToWidth));
            if (srcHeight < image.Height)
            {
                srcWidth = image.Width;
                top = (image.Height - srcHeight) / 2;
            }
            else
            {
                srcWidth = (int)Math.Round(image.Width * ((double)image.Height / srcHeight));
                srcHeight = image.Height;
                left = (image.Width - srcWidth) / 2;
            }
        }
        using (Graphics g = Graphics.FromImage(bitmap))
        {
            g.SmoothingMode = SmoothingMode.HighQuality;
            g.PixelOffsetMode = PixelOffsetMode.HighQuality;
            g.CompositingQuality = CompositingQuality.HighQuality;
            g.InterpolationMode = InterpolationMode.HighQualityBicubic;
            g.DrawImage(image, new Rectangle(0, 0, bitmap.Width, bitmap.Height), new Rectangle(left, top, srcWidth, srcHeight), GraphicsUnit.Pixel);
        }
        finalImage = bitmap;
    }
    catch { }
    try
    {
        using (EncoderParameters encParams = new EncoderParameters(1))
        {
            encParams.Param[0] = new EncoderParameter(Encoder.Quality, (long)100);
            //quality should be in the range [0..100] .. 100 for max, 0 for min (0 best compression)
            finalImage.Save(filePath, jpgInfo, encParams);
            return true;
        }
    }
    catch { }
    if (bitmap != null)
    {
        bitmap.Dispose();
    }
    return false;
}

Answer 2

您需要获取目标大小与实际大小的比率.缩放较短的一面,直到它接触实际图像大小.从中心开始裁剪并将其缩放到所需的大小.

这是代码:

 public static Image ResizeImage(Image imgToResize, Size destinationSize)
        {
            var originalWidth = imgToResize.Width;
            var originalHeight = imgToResize.Height;

            //how many units are there to make the original length
            var hRatio = (float)originalHeight/destinationSize.Height;
            var wRatio = (float)originalWidth/destinationSize.Width;

            //get the shorter side
            var ratio = Math.Min(hRatio, wRatio);

            var hScale = Convert.ToInt32(destinationSize.Height * ratio);
            var wScale = Convert.ToInt32(destinationSize.Width * ratio);

            //start cropping from the center
            var startX = (originalWidth - wScale)/2;
            var startY = (originalHeight - hScale)/2;

            //crop the image from the specified location and size
            var sourceRectangle = new Rectangle(startX, startY, wScale, hScale);

            //the future size of the image
            var bitmap = new Bitmap(destinationSize.Width, destinationSize.Height);

            //fill-in the whole bitmap
            var destinationRectangle = new Rectangle(0, 0, bitmap.Width, bitmap.Height);

            //generate the new image
            using (var g = Graphics.FromImage(bitmap))
            {
                g.InterpolationMode = InterpolationMode.HighQualityBicubic;
                g.DrawImage(imgToResize, destinationRectangle, sourceRectangle, GraphicsUnit.Pixel);
            }

            return bitmap;

        }

像这样称呼它:

var thumbImage = ImageHelper.ResizeImage(image, new Size(45, 45));
thumbImage.Save(thumbFullPath);

Answer 3

之前做过几次，技巧是首先适应图像的高度，然后将宽度重新调整为必须减少高度的比例，然后如果仍然不适合宽度，则从宽度重复，然后减少按该附加比例计算的新缩放高度。这样，您就有了一个始终适合的缩略图，可能在 X 或 Y 中存在一些空白，但图像仍然具有相同的比例，没有拉伸。

int originalHeight;
int originalWidth;
int imageHeight;
int imageWidth;
int requiredHeight;
int requiredWidth;
double scale;

if(originalHeight > requiredHeight)
{
    scale = requiredHeight / originalHeight;
    imageHeight = requiredHeight;
    imageWidth = originalHeight * scale;
}

if(imageWidth > requiredWidth)
{
    scale = requiredWidth / imageWidth;
    imageWidth = requiredWidth;
    imageHeight = imageHeight * scale;
}

然后使用对象将其绘制成这个大小的Image新对象BitmapGraphics