Image Editing: Saving, Cropping, and Resizing C# Tutorial

In C# it can be tiresome to do certain image editing functions using GDI+. This post has some fun editing methods which can come in handy at times. I have also included a nice little C# program to show all the functionality of the methods below.

Saving a Jpeg
The first thing to do here is set up the method signature with the input parameters. These are the save file path (string), the Image to save (System.Drawing.Bitmap), and a quality setting (long).

private void saveJpeg(string path, Bitamp img, long quality)

The next few things to do are setting up encoder information for saving the file. This includes setting an EncoderParameter for the quality of the Jpeg. The next thing is to get the codec information from your computer for jpegs. I do this by having a function to loop through the available ones on the computer and making sure jpeg is there. The line under that makes sure that the jpeg codec was found on the computer. If not it just returns out of the method.

The last thing to do is save the bitmap using the codec and the encoder infomation.

private void saveJpeg(string path, Bitmap img, long quality)
{
   // Encoder parameter for image quality
   EncoderParameter qualityParam = new EncoderParameter(Encoder.Quality, quality);

   // Jpeg image codec
   ImageCodecInfo jpegCodec = this.getEncoderInfo("image/jpeg");

   if(jpegCodec == null)
      return;

   EncoderParameters encoderParams = new EncoderParameters(1);
   encoderParams.Param[0] = qualityParam;

   img.Save(path, jpegCodec, encoderParams);
}

private ImageCodecInfo getEncoderInfo(string mimeType)
{
   // Get image codecs for all image formats
   ImageCodecInfo[] codecs = ImageCodecInfo.GetImageEncoders();

   // Find the correct image codec
   for (int i = 0; i < codecs.Length; i++)
      if (codecs[i].MimeType == mimeType)
         return codecs[i];
   return null;
}

Cropping
The method takes two objects – the image to crop (System.Drawing.Image) and the rectangle to crop out (System.Drawing.Rectangle). The next thing done is to create a Bitmap (System.Drawing.Bitmap) of the image. The only thing left is to crop the image. This is done by cloning the original image but only taking a rectangle of the original.

private static Image cropImage(Image img, Rectangle cropArea)
{
   Bitmap bmpImage = new Bitmap(img);
   Bitmap bmpCrop = bmpImage.Clone(cropArea,
   bmpImage.PixelFormat);
   return (Image)(bmpCrop);
}

Resizing
This next set of code is a slightly longer and more complex. The main reason this code is longer is because this resize function will keep the height and width proportional.

To start with we see that the input parameters are the image to resize (System.Drawing.Image) and the size (System.Drawing.Size). Also in this set of code are a few variables we use. The first two are the source height and width which is used later. And there are 3 other variables to calculate the proportion information.

private static Image resizeImage(Image imgToResize, Size size)
{
   int sourceWidth = imgToResize.Width;
   int sourceHeight = imgToResize.Height;

   float nPercent = 0;
   float nPercentW = 0;
   float nPercentH = 0;
}

The next step is to actually figure out what the size of the resized image should be. The first step is to calculate the percentages of the new size compared to the original. Next we need to decide which percentage is smaller because this is the percent of the original image we will use for both height and width. And now we calculate the number of height and width pixels for the destination image.

nPercentW = ((float)size.Width / (float)sourceWidth);
nPercentH = ((float)size.Height / (float)sourceHeight);

if (nPercentH < nPercentW)
   nPercent = nPercentH;
else
   nPercent = nPercentW;

int destWidth = (int)(sourceWidth * nPercent);
int destHeight = (int)(sourceHeight * nPercent);

The final thing to do is create the bitmap (System.Drawing.Bitmap) which we will draw the resized image on using a Graphics (System.Drawing.Graphics) object. I also set the interpolation mode, which is the algorithm used to resize the image. I prefer HighQualityBicubic, which from my testing seems to return the highest quality results. And just to clean up a little I dispose the Graphics object.

Bitmap b = new Bitmap(destWidth, destHeight);
Graphics g = Graphics.FromImage((Image)b);
g.InterpolationMode = InterpolationMode.HighQualityBicubic;

g.DrawImage(imgToResize, 0, 0, destWidth, destHeight);
g.Dispose();

And this gives us the final code.

private static Image resizeImage(Image imgToResize, Size size)
{
   int sourceWidth = imgToResize.Width;
   int sourceHeight = imgToResize.Height;

   float nPercent = 0;
   float nPercentW = 0;
   float nPercentH = 0;

   nPercentW = ((float)size.Width / (float)sourceWidth);
   nPercentH = ((float)size.Height / (float)sourceHeight);

   if (nPercentH < nPercentW)
      nPercent = nPercentH;
   else
      nPercent = nPercentW;

   int destWidth = (int)(sourceWidth * nPercent);
   int destHeight = (int)(sourceHeight * nPercent);

   Bitmap b = new Bitmap(destWidth, destHeight);
   Graphics g = Graphics.FromImage((Image)b);
   g.InterpolationMode = InterpolationMode.HighQualityBicubic;

   g.DrawImage(imgToResize, 0, 0, destWidth, destHeight);
   g.Dispose();

   return (Image)b;
}

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