如何压缩图像？

Question

I have problem with image compression. I need to compres a lot of files (700-900kb) to files 70-80kb without loss of quality. (or small loss ) I found menu item "Save for Web & Devices ..." in Photoshop. It works great. But I don't want to use photoshop programmatically. May be someone knows how to solve this problem with other third party components or frameworks?

Thanks for any ideas!

Answer 1

.NET has a number of image decoding/encoding libraries, often tied to a particular GUI framework (eg in Windows Forms you have System.Drawing.Image and for WPF, see the Imaging Overview chapter on msdn).

There are also third party libraries specialized in image conversion/compression that you can find online (both free and non free)

Generally though, the amount of saving you get from compressing an image highly depends on the original format. If you already have JPEG photos with normal compression (quality of 85%) then there is not much you can do in terms of making them smaller except resizing them. If you have raw bitmaps (eg BMP, uncompressed/low compression TIFF etc.) then you can expect quite large savings with most compressing formats

When choosing image format, consider this:

• Photos and similar: JPEG will often do fine. Good savings with reasonable quality loss
• Screenshots and similar: PNG will generally give best results (PNG is lossless). JPEG will often create highly visible artifacts on screenshots

Compressing an already compressed image (ie PNG, JPEG etc.) with a general purpose compression algorithm like ZIP or RAR will in practice not give you any savings. You may actually end up with a bigger file.

Answer 2

You can have a look at the FreeImage project. It has a C# wrapper that you can use.

Answer 3

Imagemagick allows you to batch-processing on files and offers a everything you could possible ask for when it comes to handling of images

Eg to resize every image in folder (destroy originals) to QVGA do

mogrify -resize 320x240 *.jpg

To preserve aspect ratio do

mogrify -resize 320x240! *.jpg

If you need to traverse a directory structure, this is how you can do it in *nix based systems (also destroying originals)

find . -type f -name *.jpg -exec convert -resize 800x800 {} \;

There is also an quality switch available, see here

Answer 4

http://geekswithblogs.net/bullpit/archive/2009/04/29/compress-image-files-using-c.aspx

a little google wouldn't hurt. good luck