This is a how to on creating small file size screen captures using irfanview which is a truely great app thats absolutely free

First up you'll want to grab your self a copy of Irfanview and the plug in pack too.

www.irfanview.com

I've found that the smallest size screen captures are almost always in .png format. Irfanview has a great plugin called "png out" which really helps reduce file size even further.

Here are some examples. The following pictures are of the full desktop captured using the "CTRL+PrtScn" keys.

The first is just a normal save with irfanview in png using compression value 9. Notice that the image quality is as good as you'd see it on the screen.

File size = 122kb



This is the exact same save in .jpg format with the default jpg compression value of 80%. Notice that the image quality has been lost from that of the normal desktop. The file size has gotten bigger too

File size = 147kb



Now I'll just do a simple image crop by selecting the area I want to crop to by holding the left mouse button and dragging a box around the area then pressing "CTRL+Y" to crop. You can always resize the area after by dragging the edges of the crop selection box. This drops the file size to only 106kb, that's already a 1/6th size saving which means faster loading web pages for easier browsing.

File size = 106kb



At this stage I'll introduce the pngout plugin. The following is using the pngout default settings. Notice that the image quality is still as good as you'd get on the screen.

File size = 85kb





Now the real trick to reducing file size is to reduce the number of colours in the picture. You do get some decrease in picture quality but it's still very readable and the file size saving are huge. Here's how you do it.



Make sure you UNTICK the Use Floyd-Steinberg dithering or you'll end up with larger file sizes



The following are advanced settings for the pngout plugin that I've found give the best reduction most of the time. You want to change the "Compression level" to 9, change the "Block split threshold" to 4096, and click on the "Keep chunks" button and hit "Select none"



And if you put together the Reduce Colour Depth and Advanced png out settings you can get a file size reduction like this without compromising image quality too much.

File size = 32kb



I should point out that this will only work for simple screen captures, if you have normal photos or have a photgraphic windows backdrop then you may want to use .jpg

I think that having a 3/4th reduction is size is worth not having such a pretty backdrop while benchmarking

Don't just take my word for it, play around and see if you can find any better settings. If you do I'd be keen to know.