Here’s the original image loaded into GIMP.
Note: be sure to do any other editing that you want to on the image first, especially downsampling or upsampling (resizing). Sharpening should always be the last step that you do.
original head
http://www.crazybump.com/ <--- use this to make the bumpmap instead of the gimp tool.
how to bumpmap
bumpmap
resized
Duplicate the image by pressing Ctrl+D or right-click and select Image -> Duplicate. It might be wise to minimize the original image window now. You can open it later to compare to the result.
Right-click on the duplicate image and select Image -> Mode -> Decompose. In the decompose dialog box, select LAB. Check the “As layers” checkbox and click OK.
This will create a new window with the image decomposed into the Luminosity (“brightness”), A and B channels as 3 layers. This will allow us to isolate and sharpen the luninosity channel which is a) the most important, and b) should be the cleanest in terms of noise.
At this point I usually turn off visibility of the A and B layers in the Layers dialog by clicking on the “eyes”.
decomposed to LAB
Go to the duplicate image. Right-click and select Filters -> Edge Detect -> Edge. In the Edge Detect dialog box, select a parameter value of the appropriate size for the edges in your image. You may need to experiment with this. For the example image I chose 6.
Now convert the edges image to grayscale by right clicking on it and selecting Image -> Mode -> Grayscale. This image is going to become our sharpening mask.
Note: in some tutorials they recommend converting to greyscale and then running the edge detection filter. The premise there (my guess) is that perhaps you don’t want to find noise as edges. My thinking is that there may be an edge in color, but not tonality (e.g. transition between two light colors). Once you have converted to greyscale you may not be able to detect that edge any more. Besides, with a high enough edge detection parameter (here 6) you will avoid detecting random CCD noise as edges.
edge detect (experiment,depends in the type of texture)
The next step is to adjust the tonality a little so that areas that need sharpening are really white and anything that doesn’t need sharpening at all is really black.
Open the Levels dialog ( Image -> Colors -> Levels). Bring the black point up and the white point down to filter out any insignificant edges. You may need to play around with the exact positions of the sliders. Click OK when the image outlines the significant edges in white and most everything else is black.
How much you’ll need to tweak this really depends on the image.
levels tool (experiment,depends in the type of texture)
Now apply a gaussian blur ( Filters -> Blur -> Gaussian Blur) to smooth out the edges a little.
used gaussian blur
If you want to you can use Levels again to adjust the white and black points of the mask. I find this is usually a good idea after the blur.
used levels again (not always necessary)
Open the Layers dialog. Select the LAB image in the drop down box at the top and then click on the Channels tab.
Click on the new channel button (newlayer) at the bottom of the dialog to create a new channel. Name it “Sharpening Mask”.
Right-click in the blurred/edges image window and Select -> All. Right-click again and select Edit -> Copy. (Alternatively you can use keyboard shortcuts Ctrl+A and Ctrl+C in succession).
In the Layers dialog, make sure the Sharpening Mask channel is selected. Go back to the LAB (value) window and paste ( Edit -> Paste or Ctrl+V).
Select the Layers tab in the Layers dialog and click on the anchor button (anchor) to anchor the floating image.
copy pasted the edged image,made a new channel and anchored
Important: in the Layers dialog, click on the Layers tab and make sure the luminosity layer is selected, and is the only one selected. We only want to sharpen the luminosity channel.
Apply an unsharp mask ( Filters -> Enhance -> Unsharp Mask). You may want to experiment with the settings here. You will find that you can use much higher amounts of sharpening (than if the entire image were selected) without significantly degrading the image.
unsharp mask tool
It’s time to reconstruct our original image from the LAB components.
Right-click in the luminosity (value) window and select ( Image -> Mode -> Compose). In the Compose Options dialog, make sure that you have selected LAB on the left and on the right that the Luminosity, A and B (Hue, Saturation and Value) components are matched up with their respective images.
Click OK; this should create a new composite image.
composed image