Obviously, Photoshop and PaintShop-Pro offer pretty much the best when it comes to editing photographs. However, you do pay a price to get them and you are buying a bulk of stuff that you'll never even use. Yes, Photoshop does offer a free trial version but you still need to download and install it, then uninstall it if you don't like it or if it takes up to many computer resources etc. Personally, if all I want to do is enhance a couple of photos I wanna skip doing all that.
Here is a list of free photo editors that anyone can use without installing software or having to register to a website. I put the ones that I like the most on top, but they're all worth trying. For each one, I include instructions on which features to use to enhance your photos. By 'enhance' I don't mean trying to get rid of a pimple or put a halo over someone's head - these are steps for simple adjustments that make your photos more pleasing to look at (pimples aside) and still look natural!
I always use a specific set of adjustments to improve my photos. Some of these photo editors only avail a subset of these options, but I still mention the steps to use these options. One thing that is important is for the photo editor to let you adjust the enhancement level - particularly since each camera is different. For example, if you are applying sharpness there should be a slider that lets you decide how much to apply - rather simply having an enable/disable option. In 'Instructions to enhance your photos', I provide a set of these levels that would work for a large number of photographs taken using point-and-shoot digital cameras, that is, they should improve the look of those photos. If you are using an SLR camera you would probably need to lower these levels (particularly the color saturation level).
These are the photo editors along with the set of options that I usually use to enhance my images (see 'Instructions to enhance your photos' for a list of levels that correspond to these options):
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Picnik
This flash-based application has an attractive tab-menu. You can use sliders to make adjustments to your photos. The reason why it is my top choice is because it gave me slider control to more functions that the other editors.
Load your image by selecting Upload image.
Under the Edit tab:
To adjust global contrast:
Exposure tab: use Contrast slider
To adjust contrast non-linearly:
Exposure tab: use Exposure slider (note that exposure adjustment is a type of non-linear contrast adjustment)
To adjust local contrast:
Exposure tab: select 'Advanced' button and check 'Local Contrast' - then use Strength slider that appear underneath. Other options here include targeting highlights and shadows separately (hint: try increasing both), as well as histogram adjustment.
To adjust color saturation:
Colors tab: use Saturation slider
To adjust resolution-detail:
Sharpen tab: use slider to control amount of Sharpness, 'Advanced' button lets you adjust for the type/size of sharpening element (i.e. what types of details to enhance) using the 'radius' slider.
To save image:
Select 'Save & Share' tab to save your photo as an image file. You can save as BMP for loss-less storage, or as other type of files. If the file size is an issue you can save the image as a JPEG. Then you need to set the JPEG quality factor - the default (8) or 9 are more than sufficient unless you're processing astronomy images.
Disadvantage: if the image is large (many MBs the sliders are not very responsive, particularly for the Local Contrast effect).
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Pixlr
This one is a really fast and responsive photo editor and the great thing is that it looks very much like Photoshop. Its interface lets you use either sliders or enter numeric values when making image adjustments.
Load your image by selecting 'Open image from computer'.
Menu selections:
To adjust global brightness and contrast:
Adjustment / Brightness & Constrast: usually only want to adjust contrast. Range -100 to 100, usually a +10 is good enough.
To adjust color saturation:
Adjustment / Hue & Saturation : Saturation to +10 to +15 (do not adjust hue or lightness sliders).
To adjust contrast non-linearly:
Adjustment / Curves ...: draw curves to adjust contrast and brightness in a non-linear way by adjusting the curve (hint: you can click multiple times on the curve to produce new curve-control points, but I would stick with using only 1 or 2 points because this could quickly get out of hand!)
To adjust contrast non-linearly (2) - optional:
Adjustment/ Exposure: non-linear contrast enhancement (like gamma), no need if you're able to use Curves, but good if you can't get a good handle using Curves. This is a very sensitive control so don't go crazy with it.
In general, don't overdo it with the levels! (see 'how-to-enhance-your-photos').
You can also try out:
Filter/ Sharpen, Filter /Denoise, and Filter/Mimic HDR, but since there are no adjustment controls there then these will probably not work that well for your photo.
To save image: File/save...
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LunaPic
Upload image
To adjust global brightness:
Select Adjust / Brightness (usually not very useful)
To adjust global contrast:
Select Adjust / Increase Contrast or Decrease Contrast
To adjust contrast non-linearly:
Select Adjust / Exposure (don't overdo it as it is very sensitive)
To adjust color saturation:
Select Adjust / Color Saturation
To adjust resolution-detail:
Select Adjust / Sharpness (only one setting though, so it is very likely that this will not work for you).
To save image select File / Save as.
Disadvantage: the max dimensions you can work with is 1560 x 1560.
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FotoFlexer
Load you image by selecting Upload Photo
To adjust global brightness and contrast:
Under the Basic tab select the Contrast icon to adjust the global contrast using a slider, as well as the global brightness.
To adjust color saturation:
Under the Basic tab select Adjust icon that shows up below the tab. Then, use the Saturation slider to increase color saturation.
To adjust contrast non-linearly:
I was excited to find that under the 'Geek' tab (I don't know why I looked under there) you can select the 'Curves' icon that will let you adjust the brightness/contrast of your photo in a non-linear way by adjusting the curve (hint: you can click multiple times on the curve to produce new curve-control points, but I would stick with using only 1 or 2 points because this could quickly get out of hand!)
To save image select 'save' button on top tab (can only save as JPG or PNG).
Disadvantage: I found this to be a lot less responsive (slower) than the previous two photo editors.
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Before and After Enhancement
Before and After Enhancement
Before and After Enhancement
Before and After Enhancement
Before and After Enhancement
Before and After Enhancement