What I do to store my pics on my HDD is to compress them in png. The average gain is about 50%, that's not a lot but if you don't have too many screenshots and a lot of empty space on your disc you can do that. The advantage is that the quality remains the same so you can modify it as many times as you want and avoid to see it get compressed every time you save it. When you're done with editing, you can save it in jpg, to post it here for exemple .

I won't enter in the details, but basically compression codes the pic differently than in bitmap. The bitmap format codes every pixel on a predefined number of bits. When you compress the pic, the programm will code the pic depending on the color areas. This isn't very clear so I will give you an exemple .

For exemple you have a pic of a flag. Say a Blue, whit, red flag (french flag ). When it's still in bitmap, each pixel is clearly coded. During the compression, the prog will code it differently so it says : "theres one area which is blue, width XX, height XX, location on the pic XX, there's one which is white, and so on. Then format like jpg use other methods and it's why too much compression kills the pic.

So that's basically how it works, just a temporary definition so you can see what it's like but I'm sure other simmers will elaborate . Btw I know that what I've written isn't very clear .

Cheers
-Seb

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Effective, but it's not really a compression method. I find that, on 1152x864 desktop resolution, with 17" monitor, anything below 800x600 pixels just looks too small on the screen. I know for a fact that there will be a good deal of people with higher resolutions/smaller monitors than me, and so the size of the picture will be reduced ever more.

Whatever it may be, screenshots or photos, if I'm posting them online, I'll stick them at 800x600.


Back to the original question...

You may find that when shrinking an image in Irfanview, it tends to make the picture much softer than before. This can also give the impression of heavy compression (no rhyme intended!), what with the edges in the picture being less defined. The best thing to do, is to find a program that doesn't soften the images (i.e. Photoshop, or any freeware alternative), resize the image, then open it up in Irfanview and compress.