issue after changing the color of the UV image with photoshop I am using texture paint and I have used different photos to do so, and the color of the skin is slightly different (in the green circles):
To correct this problem I have open the UV image in photoshop and use the split frequency technique to have one picture in greytone which corresponds to the detail (also know as high pass filter in photoshop) (here is a sample) 
and then uniformed the color as you can see 
Every thing work fine up to this point but when i import the modified UV image I get this strange result: 
(the line matches with the wire frame).
Does someone knows how to fix it? or how to make a split frequency to get something similar to the high pass filter in photoshop but with the node editor?
On your 3rd image you can see that on each polygon border on your UV layout the color are brighter, this probably happened in Photoshop for some reasons. This is what causing the wireframe pattern on your last image.

To do the same thing in the node editor you should use a Color Ramp node, which will convert your RGB image to a grayscale image. Then you can control your skin color with a RGB node.