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Reducing an image's file size by reducing it's image quality using Irfanview

The purpose of this guide, is to teach you how to reduce the file size of an image by reducing the quality of the image, using Irfanview.
There are two ways to reduce the file size of an image, reduce the actual size of the image, or reduce the amount of information stored in the image file, while maintaining the image size.
In this tutorial, I'm going to discuss the latter, reducing the amount of information stored in the image file, thus creating a smaller file size.

A couple of the reasons you might want to reduce image quality are:

    * To reduce used harddisk space.
    * To make E-mail and web pages load faster. (especially important to people using a dial-up connection)
    * To post to forums.

A short Flash presentation is available for viewing. I suggest you watch the presentation first, as this will give you an idea of what this Tutorial will cover.
The written Tutorial, will give you a bit more detail about Reducing an image's file size, by reducing it's quality.
Reducing Image File Size by Reducing Image Quality Video

Tools Needed

    * Irfanview  (download)


   1. Open Irfanview, and click on File, in the Toolbar, and select Open.


2. In the box that opens, navigate to the image you want to reduce the file size of, and select it (single Left click).
Now click the Open button.

3. The image will open up in the Irfanview window.
Once again, in the Toolbar at the top, click File, then select Save As....

4. When the Save Picture As... dialog box opens, you will see 3 check boxes at the bottom.
Make sure there is a checkmark next to the box labeled Show options dialog.

5. This will open the JPEG/GIF save options dialog box.

At the top of this box you will notice a slider next to Save quality: with lowest, and best, on it.
This slider is what is used to reduce image quality.
Lowest, will reduce image quality, Best will increase it.
Default is 80.
There is no discernable ratio I can see, as to the number displayed, and how much quality is reduced.
It has more to do with the amount of information stored in the image.
This is something you will have to play with, until you get an image that is acceptable to you.

As a sample, I took an image that was 1024 x768 pixels, had a file size of 2.25 MB, and tried saving it at different settings.
These are the results:
2.25 MB - slider set at 100 (good for making prints)
93 KB - slider set at 75 (reduced it quite a bit, but it's still a large file)
57 KB - slider set at 50 (acceptable quality for E-mails, web pages, and most forums)
33 KB - slider set at 25 (acceptable quality for E-mails, web pages, and most forums, but fine detail is lost)


6. Once you have made your choices, pick a place to save the image file, name the file, choose a file format (.jpg will give the smallest file), then click the Save button.


You now have a reduced quality image, of the original.
It sounds harder than it actually is, so give it a try.
Just remember:
Lower settings - less space, but less image quality (suitable for E-mails, web pages, and forums)
Higher settings - more space, but better image quality (suitable for making prints)


Note 1:
Something to remember is, image quality isn't as big of an issue once you reduce the size of the image.
The fine detail, that you lose by reducing the quality of a large image (1024 x768 pixels), isn't as noticeable in a small image (320 x 240).
So when you reduce the size of the image to send it in an E-mail, it won't look nearly as bad as the full sized, quality reduced, image.

Note 2:
If you're going to reduce the quality, and size, of an image, I suggest that you resize it first, then reduce the quality.
This gives Irfanview more information to work with, when resizing, thus creating a better image when the quality is reduced.