RIOT, the Radical Image Optimization Tool
RIOT is a somehow magical tool run by elves or little fairies or something. I'm not sure how it works. But it optimizes your images and lets you convert between jpeg/gif/png freely. It is also available as a DLL plugin for "The GIMP, IrfanView, XnView and other supporting applications". It works on Windows only. There is also a plugin available that adds support for RAW and HDR formats.
It can be very simple, with just a few clicks you can shrink file sizes down to almost nothing. I've had images go from hundreds of megabytes down to the low double digit range. And I don't even know what I'm doing! There are a lot of sliders and checkboxes and different settings that I don't mess with.
There are some minor adjustments you can make too, brightness/contrast/gamma. You can also strip metadata if you want.
It's a great tool that I think everyone (who uses Windows) should have. I think Irfanview already has it as a plugin, but the standalone tool is great for quickly shrinking a file.
I took a small screenshot of the forum here, and used RIOT to optimize it. The screenshot was taken with Windows 7's clipping tool and saved as a PNG.

Original: 18.1k

Optimized: 6.63k
Now, I optimized this image using 16 colors, an option I had because Scot's uses a lot of blues so taking it down to 16 colors wasn't a big deal. You can tell it was optimized but it's hardly noticeable. Saving it as "256 Colors" still reduced the filesize to 8.87k. True Color still had it down to 16.8k (admittedly a much smaller savings of space!)







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