There are a couple of ways that you can adjust photos that are often provided as "auto" features in image-editing software:
- Auto levels
- Auto contrast
- Auto colour
Levels (if you select "Image" > "Histogram" in Irfanview) are the distribution of pixels. Each pixel has an RGB value between 0 and 255. Depending on lighting, especially if you crop out a bright or dark patch, you may find your image only occupies part of this range - it is not using the full bit-depth available to it. Auto levelling (available in Photoshop and Paint.NET) tries to scale everything to get the most use out of the image format. When I do adjust images, it is typically to crop them and then adjust the levels or contrast - if Photoshop's automated routines doesn't quite get it right, I do it manually instead.
Auto contrast and auto colour - does what it says on the tin. It tries to guess what a good result is by looking the histogram and adjusting each of the colours (and where the colour peak is) independently.
Della, I recommend giving Paint.NET a try if you want to tweak your images more. It is free and has the auto-levels (as well as manual level control) as well as the typical image adjustments - brightness, contrast, hue and saturation.
Personally I'm not too keen on Irfanview's auto-adjust colours, as out of your four photos (and one I tried of my own), only the first one is an improvement to my eyes. The rest are too garish and you lose detail, especially in the photo of the anthers (fourth image) but also in the Iris beard (fifth image) and what I think is a flower pistil (the third image). The stems in the second photo definitely needs adjustment (it looks like it has a colour cast on it), but Irfanview overdoes it to me.
