Reducing a Jpg image size

If you find that your JPEG files are too large (for example, to send by mail or to publish to a web page), here are 4 steps to reduce the size of files:

Step 1 (optional!): Skip GREYCstoration on the image

GREYCstoration can remove the "grain" or "sanded" with a picture. This was generally the consequence of allowing a higher compression JPEG.

Step 2: Reduce the resolution

For example, if you take a photo with a digital camera 5 Mega-pixels, the dimensions of the image will be 2592 pixels by 1944, which is far too big for a web page.

Reduce the resolution, eg 640x480 or 800x600. This is sufficient to have a clear and precise.

Software used: XnView, Gimp, etc.. A program like XnView is able to reduce the size of a group of images at once.

Step 3: Lower quality

When there is JPEG, you can choose the quality (between 1% and 100%):
• 1% is the lowest quality, but also gives smaller files. The higher the percentage is low, plus the final will be small, but the image quality will be degraded.
• In most cases, a quality of 40% is sufficient.
• If it does not go up from 10 in 10 until the quality is acceptable.


Programs like The Gimp, you can see in real time the result of compression (by moving a cursor).

With XnView you can reduce the percentage of a group of images at once.
In the JPEG recording options, plus percentage, also check the optimization of Huffman tables (if available).

The progressive JPEG option has virtually no impact on the size, but is useful and recommended for web pages (faster display of images when they are partly responsible).

Step 4: Remove unnecessary information

JPEG files can contain many things besides the image itself: a miniature of the image, the parameters of the software that created the file, the camera settings (focus, exposure ...) .

For example, digital cameras typically add 10 kilobytes each JPEG file.
All these parameters are useful locally (for example, to organize your photos), but are useless in some environments (eg on the web).

(The browsers do not use any of this information. They are sent for nothing.)

It is possible to delete such information "useless" with a program like PureJPEG (free):

http://www.yafla.com/papers/purejpeg/filter_unnecessary_jpeg_info_such_as_exif.htm

It is a command line program. Run it as follows: purejpeg monimage.jpg

Conclusion

With these 3 (or 4) steps, particularly by playing on the resolution (step 2) and compression (step 3), you should find the optimum setting.

For you to try to find the right balance between resolution, image quality and file size in order to avoid major degradation of the image file.