I have and use Image Composer and Photoshop but I still LOVE Google's Picasa because
1. It's free
2. It is soooooooooooo user friendly
3. It is extremely versatile...
4. It is so quick and easy.
As you can see in just these few there is great variation in color in my collection of photos....and I wanted them ALL to be sepia (brown) tones since there will be so many of them on the quilt....
Picasa has an "effects" selection of choices and one of them is "sepia" so my first step was to apply that to all the photos I wanted to use...But even with all of them being sepia there was still more variation in tone than I wanted.
Third down on the left....it is a choice I use on all photos, colored or not, which are to be printed on fabric... Color is always lost in that process so intensifying color in the beginning makes for a better end product. But in this case I'm using saturation to put many photos into balance. But as you can see the tools include sharpening, changing to B&W, tinting, adding a glow and soft focus among others... There are many other tools in the basic fixes and tuning sections.
On most of the effects tools there is this simple bar and button.. You can slide the button either way and watch the change in your photo as you use it and before you hit the apply button... VERY low tech here...
So using this simple technique you can see how I was able to make my photos very even in tone... Not only easily but quickly.
Just as a follow up note... To get the pictures of the Picasa tools I actually took a picture of the computer screen as it was something that was not downloadable... I do this quite often but the last time I posted about it I received such a negative response from one follower that I was hesitant to confess again... Hopefully that follower has moved on...if not I already know how you feel on this subject..!!!