This Photoshop tutorial will tech you how to make a stone wall easily and
quickly. In this case it is in a circle, but could be done to any shape
to represent any wall, or even a floor surface.
1. Create a new image (mine was 800x800) with a transparent background,
and put a set of grids in the center, horizontal and vertical (select
Show Rulers first):

2. Make a selection of the shape you want. To do this one I used the
elliptical marquee tool, Alt then Shift to make it select from the
center and constrain it to a circle I then used the tool again using
Alt (click the center) release Alt then Alt again then shift to cut the
center circle out:

3. Go to the Channels tab, create a new channel and name it "shapes".
4. Apply the Stained Glass Filter (Filter/Texture/Stained Glass), with the following settings:

This will make your "shapes" channel look like this:

Changing the cell size and border thickness will change the size of the stones and the mortar gap that will appear between them.
5. Now apply the cutout filter (Filter/Artistic/Cutout) with the next settings:

Apply it again with the same settings (just press CTRL+F)

This will make the stones look smoother. You can adjust these settings,
or even leave out this step to have more angular stones. AT this point
you might have to touch up the stone pieces if some are too small or
angular looking by using the pencil and eraser tools on the channel.
6. Now we start to make the stone... Hold CTRL while you click the
"shapes" channel thumbnail, this will make a selection that contains
the white areas, so invert the selection to get the stone shapes
selected. On Layers tab, create a new layer, "Stone 1" and fill the
"Stone 1" layer with any colour (I used blue). Keep the selection.

7. Expand the selection by 5px (or half your border thickness in step
4) create a new layer, "Mortar" and fill it with any colour (I used
red). Drag this layer below the "Stone 1" layer.

8. Now go back to the "shapes channel and CRTL click on the thumbnail,
then invert the selection again. Now feather the selection by 5 px (or
about 1/4 of the cell size in step 4). Make a new layer, name it "Stone
2", use the paint bucket and fill it again (I used green). At this
point you should have 3 layers:

9. At this point, you will have to back to the "Mortar" layer and use
the circular marquee tool to select out and erase the mortar where you
don't want it on the outside and inside.

10. Now you need to apply some finishes to the layers... I used Bevel
and Emboss with a texture plus a colour overlay (grayish) on the
"Mortar" layer. Play with the different textures and colours until you
get ones you like. On the two "Stone" layers, I used Bevel and Emboss
with a texture plus a colour overlay plus a drop shadow. I just kept
fiddling until I got the look I wanted...

11. The last step was to select the non-image area using the magic wand
(all layers, tolerance 0, non-contiguous), inverting the selection and
applying a shadow around the whole thing (I used the Eye-Candy Gradient
Glow plug-in but there a large number of tutorials on the web for doing
this). I also selected the "hole" and applied a transparent gradient
fill to make the shadow "inside" the ring more pronounced:

That was it, export as a PNG and viola!
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