Showing the Reflected Light a Polarizing Filter Eliminates from a Scene

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Want to see how much reflected light your polarizing filter eliminates from any scene? You can easily visualize this light using an image editing program like Photoshop.

Photography enthusiast Michal Zalewski captured the “reflected light” photograph above showing a room in his house. He started by shooting two photographs of the scene. The first was shot with a polarizing filter killing the reflections on the lower surfaces:

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Keeping the camera stationary, he also captured a frame showing the scene with that same filter rotated 90 degrees. This shows the scene with those reflections still present:

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He then subtracted the RAW 16-bit photographs “from each other” in order to capture “just the information about the reflections in the scene”:

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At this point, you can do various things with the information you have, including selective colorization, dodging, burning, etc. Here’s the photograph with the reflected light turned into monochrome:

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…and the same photograph with the scene in monochrome and the reflected light in color:

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Zalewski says it wouldn’t be difficult to build some kind of rig that could automatically gather information about reflected light for you, but he has yet to find a useful photographic application for the technique.

(via Michal Zalewski via Reddit)

Image credits: Photographs by Michal Zalewski and used with permission

  • branden rio

    Physics fail… all the light in the photo is reflected.

  • Kenneth D. Aston Jr.

    lol very true

  • Yves

    Mmmm… Doesn’t the title clearly say that this is the reflected light which is eliminated by the polarizing filter? So, just the reflected light which is filtered out by the polarizer?

  • a.j.

    Reading comprehension fail.

  • Wobble Stand

    Yawn. Let me know when Photoshop can do this with refracted light.

  • Nate Curde

    Very interesting to look at the image showing the delta in light, after the subtraction is done. There are a surprising number of surfaces reflecting light that are not where you would expect much to reflect. The bike & stroller show this well. It also highlights where there is a loss of some detail by not having the contrast provided by the reflected light.

  • Julien

    I tried the same thing a couple of weeks ago with a flash. I took a picture without the flash, then a picture with the flash, substracted and ended up with a picture as if it had been taken in complete darkness with only the flash. The same thing works by blocking any light source. For example if you take a portrait in direct sunlight (you need to make sure your subject doesn’t move for two pictures), then take another portrait but make a shadow on your subject, then substract, you end up with only the light where the shadow is on the second image, so it sort of transform the sun into a round projector (or any shape you want). It’s pretty cool what you can do with this technique!

  • Adam Cross

    what does “subtracting images from each other” actually mean? i’m playing the stupid card but I don’t really know what he’s doing here.

  • Theranthrope


  • handsome guy

    Its in photoshop’s blend modes.

  • Adam Cross

    how am I stupid enough not to realise that? :| whoops

  • Chris

    Companies that scan peoples faces for computer games and motion picture special effects are using this type of capture for gathering skin reflectance information so they can recreate the skin more realistically.

  • JonathonWatkins

    Mmmm, the polarised images looks more contrasty to me than the unpolarised one, not less. It looks punchier and you can see the details of the stroller more clearly.