This is my first “play raw”, and also possibly the first image I ever processed start-to-finish using high bit depth GIMP 2-9 built from git, back in 2013, using dcraw to output a scene-referred image file.
Back in 2013 I never managed to produce a final image that I actually liked. So all these years later I decided to try again using GIMP-2.10, this time using darktable to make a scene-referred rendition via the darktable GIMP plug-in:
080724-1822-100-1479.cr2 (9.0 MB)
Raw file licensed CC-NC-SA (Creative Commons — Attribution-NonCommercial-ShareAlike 3.0 Unported — CC BY-NC-SA 3.0).
080724-1822-100-1479.cr2.xmp (6.7 KB)
CameraRGB-elle-V4-g10.icc (892 Bytes)
The scene is the rapid departure of a violent rainstorm. Imho the image composition isn’t too awfully bad though I wish the capture had been shot with a slightly wider lens. But after interpolation, I found (and still find) it difficult to process the scene-referred image into a satisfying final image:
-
It’s a high dynamic range image, by which I mean that a reasonable placement of middle gray - for example put middle gray on the green grass in front of the white utility building - will push the RGB channel values of much of the cloud-covered portions of the sky well past 1.0f and in some places past 2.0f. There aren’t any blown pixels in the raw file because I exposed for the clouds. However, in darktable the white balance multipliers drove the red channel values of the darktable output above 1.0f in small portions of the brightest clouds.
-
I shot the scene through a green-tinted passenger-side front window of a car going maybe 45 mph down the road, just as the storm had come to an end. So portions of the lower right corner of the scene are distorted and obscured by rain drops and wind-blown debris that accumulated in the lower right corner of the window. Back in 2013 I made an effort to repair the damage, but this time I didn’t even try, wanting instead to concentrate on tone-mapping.
-
The camera white balance is “uniwb”. Normally for midday sunny-ish outdoor scenes in the raw processor I would just use Daylight white balance. But that wouldn’t remove the green tint from the car window. So I white-balanced the image on a white cloud.
After transferring the image from darktable to GIMP-2.10, I made several black and white renditions, but none of them sufficiently conveyed the impression that a storm is being pushed out of the scene. Here’s the one I liked the best (and I don’t like it very much):
To try to better capture the idea of a departing storm, I added the color information back in to the tone-mapped black and white rendering using GIMP’s “Luminance” blend mode over the base “from the raw processor” color layer. The resulting color image had a slight overall red color cast - the white portions of the clouds weren’t as neutral as they seemed when looking at the dull scene-referred image in the raw processor.
To remove the red color cast, I re-white-balanced the base color image on the roof of the white utility building (still using GIMP, but first converting the image back to the camera input profile). This made nicer sky and cloud colors, but the vegetation colors still weren’t right.
So I took the re-white-balanced color rendition into RawTherapee and used the CIECAM02 module to further modify the white balance using chromatic adaptation, and then continued working with the image to try to capture the sense that a storm had just ended. Here’s the result so far:
For both versions shown above, all “tone mapping” was done in GIMP-2.10, using masks and layers plus basic editing tools: Exposure compensation, Levels, Curves, and layer blend modes. I didn’t use any dedicated tone-mapping algorithms. This is the way I usually - well, always - process images, and usually I’m happy with the results.
But my two renderings of the departing storm clearly have a lot of room for improvement. So I’m hoping to see what other people might do perhaps using more sophisticated tone-mapping tools - there’s a lot of such tools out there - which to use? where to start?
