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Reducing the Size of Image Files

So you've scanned some photos or downloaded them from your digital camera and you want to post them on your web site. You will need to reduce the size of your image file before you upload it - even if you and all your friends have high speed connections. The dimensions may well be too large to display without scrolling and the file size may be so large that the download time is unacceptable. The ideal way to do this is with a professional image editor such as Photoshop.

A very good (and inexpensive) alternative is a free graphic editor called Irfanview, available for download at http://www.irfanview.com. This is a fairly small file (821 KB) so it should download quickly even if you have a dial-up connection. After you have downloaded it, double-click the file to start the installation. Once installed, this programme will allow you to reduce the size and dimensions of your graphic files and at the same time maintain an acceptable level of quality. Before making any of the following changes make a back-up copy of your original file.

Reduce Dimensions

There are three main things you can do to reduce file size. The most obvious, and sometimes most necessary change you need to make is to the dimensions of your file. This can be done with Irfanview by choosing the menu options Image and then Resize.

If you make sure that the Preserve Aspect Ratio checkbox is ticked there will be no distortion when you resize your image. The above image itself was resized using Irfanview. Originally 507 by 418 pixels, it was reduced to 400 by 329. An ideal size for pictures on a web site is about 400 by 300 pixels for a screen resolution of 600 by 800. As you increase screen resolution you may make your image proportionately larger. Most users set their screen resolution to 800 by 600 pixels or 1024 by 768 so don't make the dimensions too large.

Reduce Colours

Additionally, you can reduce file size by decreasing colour depth. This is done by choosing Image and Decrease Color Depth from the menu. To the right is a screenshot of the window that will open.

If your image is 256 colours, click on Custom and type in "128". As opposed to the resize window this image has not been manipulated at all. You will notice that it is of superior quality to the resize window.

Reduce Quality

Another step you can take is to reduce the quality of the picture. This may be done by choosing File, Save As, and Options from the menu. Decreasing the Save Quality of your picture will reduce its size.

After you have made changes to your picture, view the result. You may be able to compensate somewhat for the loss of quality. For instance, if you have reduced the size of a picture you can usually improve its appearance by sharpening it.

As you might have guessed, all the steps noted above will reduce the quality of your picture. Remember, always keep a copy of the original. The point of reducing the size of your image is to reduce download times and storage space. The image presented on the internet will not be as good quality as your original but it will be there for others to view.


by Peter Lavin

About the Author

Peter Lavin runs a Web Design/Development firm in Toronto, Canada. He may be reached at peterlavin@sympatico.ca.