How to resize images for display on the web
Digital images get large quickly. My Sony DSC-P31 takes 800K for each picture.
So if you are downloading one of my pictures over a modem, you'll spend (800K divided by 4K per
second = 200 seconds = ) 3+ minutes per picture. Additionally, space on the web
is usually limited.
Our goal is to get each image smaller then 50K without losing much.
Get an image editor
My favorite program
for this is called IrfanView and is available for free download from
IrfanView.com (817K).
If you go looking for your own image editor, you'll need something that can:
- read whatever format you start with and write JPG or JPEG (same thing).
- crop
- resample or resize. Resampling gives better results.
- save JPG's at different compression ratios. (Okay, this isn't really that important)
Make Copies
It's so easy to make a copy of your original that it is silly
to risk your only copy of the perfect picture.
I'm going to just assume that you know how to use Windows Explorer to
copy and paste your pictures to a new directory
Save with Compression
The JPG (or JPEG) image format is built around a method for compressing images
of the real world. (The GIF image format is optimized for 2D computer graphics.) The first thing to do is to tell IrfanView (or your program
of choice) to use 80% compression for JPG's (My rule of thumb.)
With an image loaded, go to the File menu, select "Save As". Select the file type
JPG - JPEG. Then press the Options button.
Move the slider to 80%. It's a good comprimise between quality and file size.
Here's a quick comparison.
80%
37K
|
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30%
18K
|
|
While this looks okay on first glance. I'm didn't like the lack of clarity on my neice's face.
|
20%
15K |
|
Things are starting to get blocky.
|
10%
11K |
|
|
5%
9K |
|
The bad pictures are here as a demonstration of how the JPEG compression scheme works.
It records gradient areas which are really common in pictures and more rare in computer
graphics.
|
Play with it and find a result you like. IrfanView will load back up with the
last setting you gave it. You may want to check that it's what you want before
you save your work.
Toss The Junk ->
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Copyright Tom Cerul 2003-2010