How can I light glass bottles and drinking glasses for a still life using only two flashes?

Question

I want to photograph 2–3 Cognac bottles with some drinking glasses, grapes, and leaves on an old wooden desk. I have two speedlights (Canon 580EX II and 430EX II), umbrellas, a snoot/grid, gels, a reflector, and a large background that I can also use as a flag/gobo.

Most tutorials for glass still life seem to use three lights or more. Can I still get a good result with just two flashes? I'm mainly struggling with how to arrange the lights to get smooth lighting on the bottles and glasses without ugly hard reflections. Any practical setup advice for working with glass using only two flashes would help.

user28357 · Answer

You can get to the desired result with post processing of pictures taken at different lighting conditions. You must make sure the camera is mounted on a tripod, and that nothing in the scene moves. You take the pictures such that the light source illuminates the scene from different angles so that the reflection is at different places at each picture. For every spot in the scene there should always be at least one picture where there is no reflection at that spot.

You then align all the pictures (even pictures taken on a tripod will drift slightly in alignment), and transform them to linear colorspace. The next task is to add up the pictures using masks that block out the reflecting parts of each picture. Here you need to be careful with introducing artifacts due to a contribution from one part suddenly missing. You can do this by considering the regions around the reflected areas, you can find an approximate linear combination of the other pictures that is a close approximation to these areas.

Suppose that the region slightly away from a reflection in picture 1 is well represented by 0.4 X + 0.6 Y where X and Y represent the gray values of the pixels from pictures 2 and 3. Then you make a hard mask that covers the reflected area plus a bit more, say 12 pixels around the reflected area. Then you apply a Gaussian blur of a few pixels radius to the mask, which makes the mask gradually transparent in a small region away from the 12 pixels distance. You then replace picture 1 by

(picture 1) * mask + (0.4 picture 2 + 0.6 picture 3) * (1- mask)

This has the effect of seamlessly replacing the reflected area from picture 1 by the closest approximation from the other pictures. After having erased all the reflections, you can add up all the pictures and convert back to sRGB. Because we're working in linear colorspace, the linear combinations we take could have been obtained by applying some (possibly very complex) way to illuminate the scene (except when negative coefficients appear), the result should therefore look natural.

How can I light glass bottles and drinking glasses for a still life using only two flashes?

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