True RAW highlights clipping in a snap

Started Feb 25, 2018 | Discussions thread
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Ciriaco Garcia Regular Member • Posts: 345
True RAW highlights clipping in a snap
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Aiming to compare my camera zebras with the true RAW zebras I have developed a new tool for the PC. It is also useful to exactly know your images exposure, since even RAW converters don't actually show the physically overexposed areas in the images.

The tool generates a highlights clipping representation from the true RAW data and stores it in new sidecar images (appending "_clip" to the original RAW file name). Most camera models should be supported. These images are generated very quickly, in about 2-4 seconds for each RAW photo. This is how they look like:

The original picture is developed into B/W to emphasize the overexposed areas. To be more exact, the image is converted to black and bright gray, since pure white is reserved to show clipping in all channels. Anything in color or bright white is overexposed in the RAW data. The color coding is as follows:

  • Red - only red channel clipped
  • Green - only green channel clipped
  • Blue - only blue channel clipped
  • Yellow - red and green channels clipped
  • Pink - red and blue channels clipped
  • Cyan - green and blue channels clipped
  • White - all channels clipped

These images use half the width and half the height of the full picture, caused by binning (instead of interpolating) the color channels during the bayer demosaicing.

The tool runs in Windows/Linux/Mac and is based on the popular dcraw application. The source code is publicly available on Github .

Windows users can download a standalone binary HERE . Doesn't requires installation: simply, extract the ZIP. Then drag your RAW files into "REVELATOR": the generated image files will be stored along with them. It is possible to drag entire folders (in that case the application will skip the non RAW files).

In addition, a histogram spreadsheet (*.csv file) can be optionally generated (edit REVELATOR.BAT with notepad and change the HISTOGRAM property near the top to 1).

Note that the generated images are big TIFF files, but if you were to store them, they could be converted in batch to jpeg e.g. using ImageMagick (you could even use exiftool to inject on them the original EXIF information, as I did in the example above).

Note: noise in high ISO photos may confuse the application, which may determine a wrong black point. That would cause the image to appear overall much brighter and dull, but has no impact in the highlights clipping. The algorithm to determine the clipping level is far more tricky but fortunately seems to work with lots of photos.

Enjoy!

 Ciriaco Garcia's gear list:Ciriaco Garcia's gear list
Sony a7R III Canon TS-E 17mm f/4L Sigma 35mm F1.4 DG HSM Art Canon EF 24-70mm F4L IS USM +1 more
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