Bas Relief is a traditional darkroom technique that in recent years has fallen out of fashion in the photographic world. The term Bas Relief in French means low relief. As with most techniques this one can be improved in accuracy and updated digitally.
In the days of the darkroom
In the dark room to create a Bas Relief image you would combine a positive and negative of the same image copied on continous tone film, which was then sandwiched slightly out of position in the negative carrier. Depending on how the the film was sandwiched would change which side the shadows would appear. The result of this could be quite abstract, with some thought needing to be given to the subject of your image. The best images used are those with strong textual or graphic qualities.
In the digital age
Photoshop does have its own filter for Bas Relief which in my opion like a lot of photoshops filters can look over the top and a little cheap.
I create my images uisng a digital version of the film method.
First I open my image. The one I have used today is of a wodden chappel in a forest close to where I live.
Next I convert the image to black and white and make some adjustments to its perspective as the image is a little skew.
As you can see I work using smart objects, this is because if I need to make changes I can when I revisit the image.
Next I duplicate my original layer twice and rename them positive and negative.
I select the positive layer and go Filters>Other>Off-Set and set the vertical and horizontal value to +1
This will misalign the layer with the one below.
I then select the negative layer and first invert the layer (ctrl + I) and then go to Filters>Other>Off-Set. This time I will set the vertical and horizontal values to -1.
Finally I set the blending mode of the positive and negative layers to Overlay.
As you can see the image is more contrasted pulling out the detail in the wood.; the effect is subtle if you wanted to try and make it more aggressive make the off-set values higher .
I have grouped my positive and negative layers to keep my layers tidy.
Next I just tidied up my image I took all my layers and created a new smart object. I then reduced the noise and sharpened the image. I also didn’t like the plaque on the wall of the chapel so I removed it and then using a curve created a sepia styled tone.