Create thumbnail and reduce image size

问题

I have very large images (jpg) and i want to write a csharp program to loop through the files and reduce the size of each image by 75%.

I tried this:

Image thumbNail = image.GetThumbnailImage(800, 600, null, new IntPtr());

but the file size is still very large.

Is there anyway to create thumbnails and have the filesize be much smaller?

回答1:

private void CompressAndSaveImage(Image img, string fileName, 
        long quality) {
    EncoderParameters parameters = new EncoderParameters(1);
    parameters.Param[0] = new EncoderParameter(Encoder.Quality, quality);
    img.Save(fileName, GetCodecInfo("image/jpeg"), parameters);
}

private static ImageCodecInfo GetCodecInfo(string mimeType) {
    foreach (ImageCodecInfo encoder in ImageCodecInfo.GetImageEncoders())
        if (encoder.MimeType == mimeType)
            return encoder;
    throw new ArgumentOutOfRangeException(
        string.Format("'{0}' not supported", mimeType));
}

Usage:

Image myImg = Image.FromFile(@"C:\Test.jpg");
CompressAndSaveImage(myImg, @"C:\Test2.jpg", 10);

That will compress Test.jpg with a quality of 10 and save it as Test2.jpg.

EDIT: Might be better as an extension method:

private static void SaveCompressed(this Image img, string fileName, 
        long quality) {
    EncoderParameters parameters = new EncoderParameters(1);
    parameters.Param[0] = new EncoderParameter(Encoder.Quality, quality);
    img.Save(fileName, GetCodecInfo("image/jpeg"), parameters);
}

Usage:

Image myImg = Image.FromFile(@"C:\Test.jpg");
myImg.SaveCompressed(@"C:\Test2.jpg", 10);

回答2:

ImageMagick is a command line tool which is hugely powerful for doing image manipulation. I've used it for resizing large images and thumbnail creation in circumstances where the aspect ratio of the source image is unknown or is unreliable. ImageMagick is able to resize images to a specific height or width while maintaining the original aspect ratio of your picture. It can also add space around an image if required. All in all very powerful and a nice abstraction from having to deal with .nets Image APIs. To use the imageMagick command line tool from within C# I recommend using the System.Diagnostics.ProcessStartInfo object like so:

ProcessStartInfo psi = new ProcessStartInfo();
psi.FileName = @"C:\Program Files\ImageMagick-6.5.0-Q16\convert.exe";
psi.UseShellExecute = false;
psi.RedirectStandardOutput = true;
psi.RedirectStandardError = true;
psi.Arguments = string.Format("-size x{0} \"{1}\" -thumbnail 200x140 -background transparent -gravity center -extent 200x140 \"{2}\"", heightToResizeTo, originalTempFileLocation, resizedTempFileLocation);

Process p = new Process();
p.StartInfo = psi;
p.Start();
p.WaitForExit();

Using the scale% paramater you can easily reduce the size of your image by 75%

回答3:

Compress your image. For thumbnails, JPEG is sufficient, as you're not looking for quality.

Image thumbNail = image.GetThumbnailImage(800, 600, null, new IntPtr());

thumbNail.Save(fileName, ImageFormat.Jpeg);

回答4:

From GetThumbnailImage's documentation:

If the Image contains an embedded thumbnail image, this method retrieves the embedded thumbnail and scales it to the requested size. If the Image does not contain an embedded thumbnail image, this method creates a thumbnail image by scaling the main image.

I'd suggest you use smaller width and height values. Try:

// reduce the size of each image by 75% from original 800x600
Image thumbNail = image..GetThumbnailImage(200, 150, null, IntPtr.Zero);

See sample code.

回答5:

This method helped me very well. Low image size, maintains aspect ratio

 ShellFile shellFile = ShellFile.FromFilePath(ImageWithPath); //original image path
 Bitmap shellThumbSmall = shellFile.Thumbnail.ExtraLargeBitmap; //change image size
 shellThumbSmall.Save(ImageWithPathThumbnail, ImageFormat.Jpeg); // new image path and format

These are needed

PM> Install-Package WindowsAPICodePack-Core
PM> Install-Package WindowsAPICodePack-Shell

using Microsoft.WindowsAPICodePack.Shell;
using Microsoft.WindowsAPICodePack;

来源：https://stackoverflow.com/questions/684092/create-thumbnail-and-reduce-image-size

标签

file

image

size

image-scaling