Using IrfanView to Adjust Brightness and Contrast
Using IrfanView to adjust the brightness and contrast of an image is quite easy to do. The first thing to do, is to open up the image that you want to adjust in Irfanview.
Then, hit shift-g. That will open up the Enhance Colors dialog box. From there, you can adjust the brightness, contrast, color balance, gamma correction, and saturation of the image. The thumbnail on the left is the original image, while the thumbnail on the right shows what the image will look like when you hit ok.
If you don't like the way the image looks, just click cancel, and it will undo your changes. If you like the way it looks, just click ok, and then save your image.