I'm a GIMP noob. Yeah, I admit it. Albeit, quickly becoming a hardcore GIMP'er and salivating over the upcoming release of version 2.8. Enough about that, let's get on with the tutorial… Let me first say, if you ever find yourself attempting a tutorial and you just "don't get it" as you're following along, or even worse – you download a script and have NO clue as to what to do with it, FRET NOT! Usually script authors will say something to the effect of "this script is based on a Photoshop tutorial, click link here…" If they do mention a tutorial, try to follow that tutorial as best you can – or – check my sitemap on Mahvin.com to see if I have covered it. I downloaded the Displacement Water .scm filter, followed the links offered by the author, and went over the instructions a few times. Not reading the instructions carefully makes a difference in whether you're going to succeed or fail in accomplishing the use of the script. That being said, because there was so much input on various links, it all got mixed and garbled in my mind, so I spent a few hours sorting it all out. If you don't have the Displacement Water script and want to follow along, follow the link to get it, but while you're at it, grab this mirror script by Saul Goode, too. The mirror script will save a ton of steps in doing the tutorial. Remember, this is the "noob version" of water displacement. The general purpose is to get everyone understanding how best to use it. Once you accomplish it, feel free to modify your colors or add new layer effects, etc. The following image (found under Vignette script on the GIMP Registry) will be used in this tutorial, copy and paste it into GIMP:
STEP 1:
If you haven't added the mirror-dup.scm script to GIMP, do it now. Once you refresh the scripts, you will find it under Script-Fu – Transform - Mirror on the menu bar. You'll see this (use the same selections as shown):
You should now have an even vertically mirrored image of a frog:
STEP 2:
Make a duplicate layer of the mirrored image.
STEP 3:
It's time to make the water displacement map. Select Script-Fu/Map/Water Reflection map on the menu bar. You'll see the following (use the selections shown):
The original frog image was 500 x 380, so that is what x and y should be in the selections above. Remember this whenever you create new water reflections (X and Y are the width and height of your original image before you alter it). You should end up with a displacement map that looks like this:
You'll notice the name of this image is red.# and it is a separate image from your frog image. We'll be pasting this map into a new layer on the frog image.
My displacement script threw errors a few times, so if it throws an error for you, try it a few more times. If errors persist, leave a comment for the script author indicating what those errors are. If you correctly identified the image width and height, you shouldn't have any problems.
STEP 4:
You should have two layers on your mirrored frog image, add a new layer to the top. With the new layer highlighted, copy the displacement map we just made and paste it into the new layer. Use the Move tool to move the displacement map over the bottom area of the mirrored image before you anchor the floating selection. When you're happy with the location, anchor the layer. Note the image below:
(TIP: After you paste the displacement map into the new layer, you can use your arrow keys to move it sideways or up and down).
STEP 5:
Add another new layer. Select the Rectangle Select tool. Select the bottom half of the picture with the displacement map.
Add a layer mask to the new layer.
Select the Gradient tool using the default black & white gradient and drag a gradient from the halfway point to the bottom. Your layers should look like this:
Notice that there are links on the displacement map and the background copy? You need to do the same thing. All you are doing is linking the displacement map to the background copy so that when you finally map the water displacement, it will show the layers for the displacement map in the lists.
I didn't name my layers, which I should, and you should make a practice to name your layers as well.
STEP 6:
Select and highlight the background copy layer just under the displacement map, and go to Filters/Map/Displace. Note the selections in the image below:
For small image reflections like this one, the only way to utilize an X displacement is to make your image selection area wider. Otherwise, you'll have to leave it at zero to avoid it leaving blank areas in your reflection area. (Check the preview when adding X displacement, you'll see what I mean). Y displacement is usually twice the displacement of X. We'll make an exception here. 
To see the result of what the displacement achieved, click the eye on the displacement layer to off.
STEP 7:
Adding color is fairly simple, just remember two things: 1) Create a selection for the lower half of the image when using colored gradients, and 2) the sky is the limit on color choices or blend effects.
Select and highlight the top most layer (with layer mask), link it to the displacement map and background copy, then select the bottom half of the image using the Rectangle Select tool, if it's not already selected.
Select the Gradient tool, and pick a darker emerald green color and a lighter shade of emerald green. See my color choices below:
Drag the Gradient tool down from the halfway point to the bottom. You can reduce the transparency, if needed. That's it, you're done!
The final product:
ENJOY!
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22:21, 29.09.2009
awesome, nice tutorial
00:38, 30.09.2009
Thanks, Michael!
11:24, 10.11.2009
Amazing , the fist pic looks original with no effects , really cool tutorial
09:49, 13.01.2010
I was looking foward to learning this but, after the first step I am getting an error. If you are aware of it or can help me fix it that would be wonderful.
13:00, 13.01.2010
What is the error? What version of GIMP are you using? Please give me the details of your error.
18:41, 27.01.2010
Hello!
Would you please help me!
I got this error at the first step:
Error while executing script-fu-mirror-dup:
Error: Bad syntax of binding spec in let* : ((work-image) (new-layer) (orig-width) (orig-height))
I'm using GIMP GIMP 2.6.7
Thaks!
19:12, 27.01.2010
Go to lines 15 – 21 of the mirror duplicate script (using Notepad++) and add zeros like shown below:
21:20, 27.01.2010
Thank you.
I upgraded succesfully.
But to be frank, I don't understand at all, your next advice. How do I found, those lines ??? *blushing*
21:42, 27.01.2010
You will need to open the mirror-dup.scm file with a text editor (i.e. Notepad++) and on the lines 15 – 21, you will see in the editor which lines I refer to. I realize this is all new to you, but fear not, I will help however I can.
23:02, 27.01.2010
I was hard, but I finally made it! Now I'll try to proceed with the instructions.
Thanks, and big hug!! It's very kind of you to help me so much.
23:43, 19.07.2010
The texture map does not display even when linked in my situation.
23:44, 19.07.2010
Display as in drop down list.
01:44, 20.07.2010
Are you selecting the background copy layer when using displacement map?
11:34, 20.07.2010
Yes but for some reason it doesn't show up in the drop down menu even if its linked. I think it may be the way i pasted it i into the project
12:15, 20.07.2010
Ok, I duplicated your problem and figured out the method. Create a new layer before pasting the displacement image map into it. Don't paste the displacement map as a new layer. Not sure why this is causing a problem, but it is.
So, remember:
1. Create new transparent layer above the copy layer first.
2. Copy the displacement map image
3. Paste the image into the layer. Adjust and fit it toward the bottom of the layer.
4. (The key here) Anchor the layer when done adjusting. If you don't get the anchor layer option, start over again. Now linking the displacement map and mirrored copy layer should allow the displacement layer to show up.