Tutorial: T-shirt

Overlays are often very clumsily done. The technique described here is very general, and can be used to overlay an image on any kind of surface.

• Start with the ingredients: a slightly rumpled T-shirt...

  A T-shirt

  ...and a slightly stupid design:

  A design

  You can get both of these in this archive; the design is in Draw format, which will give better results.
• Load the T-shirt into Photodesk.
• Open Channels and click on Layers...
• Duplicate the image into a new layer. To do this, drag and drop the layer name on to the new layer icon, like this:

  Duplicate the image

  You should have something like this:

  Two copies

• Note the top layer is the one being edited (the pencil is highlighted). All the work will be done on this layer – the bottom one won't be changed at all.
• Click on the Mask, and in the window select Work image into mask.
• Select Magic wand:Whole image, and click on the image. It should turn pinkish:

  Copy the image into the mask

• In the channels window, click on #4. This is the alpha channel, which we've just written to. The image should turn monochrome.
• Select FX:Blur>Gaussian, and set to about 6 pixels. Click on Blur. This is just to smooth out any sudden transitions.
• Now click on channel #0, type Ctrl-E and Fix. This erases the image in the top layer, which we don't need. It will look the same though, because erasing a layer causes it to become transparent and so we can see the original, bottom layer through it.

  You can check this by clicking on the #1 in the layers window – you should just see the check pattern which denotes transparency. But note that the alpha channel containing the blurred T-shirt hasn't been erased; check this by clicking on #4 in the channels window.

• Check that you're writing to the top layer, with the RGB channel enabled. Now drop the Draw design file on to the image. It will appear along with a small dialogue:

  Graphic rendering dialogue

• Adjust the Scale to about 80% or so, and move the design around by dragging the box. If necessary, you can rotate the design to match the background image. Ensure that RGB and Anti-alias are selected in the rendering dialogue, and click on Render:

  Placing the design

  Not very convincing, is it? But here's the magic:
• Fix, and open FX:Map>Displace. Set up like this:

  Setting up the displacement

  The exact amount of vertical and horizontal displacement will depend on the image; here about 4 seems right. When you're happy with the preview, click on Displace. It should look something like this:

  Displaced using the blurred mask

  What this has done is use the blurred copy of the T-shirt in channel #4 as a displacement map. This shifts pixels in an image according to the greyscale value in the map channel. So we're using the shading in the T-shirt image to determine the displacement, which gives a pseudo-depth to the result as the overlaid image follows the shading contours.

  But it can be improved a lot more...

• In the layers window, set the Mode to Multiply. This allows the shading of the T-shirt to show through. And now set the Opacity to about 80%, to give a slightly faded effect:

  It's a fake!

Notes

• You can use this technique for any nicely shaded surface: curtains, rocks, metal, people....
• The overlay doesn't have to be a Draw file – you can also use any sprite or ArtWorks file.
• You may need to experiment with the blending mode of the top layer if the background is coloured.
• It's very easy to overdo effects, in this case the displacement. It's quite subtle here, but adds considerably to the realism.

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	To overlay an image on a textured background: Copy base image into new layer Work image into mask Blur mask a little Erase top layer image Render design into top layer Apply displacement map using mask channel Adjust blend mode (eg multiply) and opacity to taste