Re: Courthouse Wash: Results

Robert Wheeler

For the petroglyph challenge, I first tried looking at channels in a number of the images, then tried some channel blending without good results.


Taking a step back, I looked closer at the IR images to see what subject features were strongest in each. Then I investigated channels of some of the IR images in different color spaces. To me, the detailing of the figures on the wall came out best in Lab color space, specifically the L channel. Stacking the IR images revealed that the one ending in 50 was out of alignment with the others, so I removed that from the stack (number mistyped in my summary sent to Dan). My entry is number 1101.Skip to bottom of message if you don't want to wade through the detailed processing steps.


I stacked the IR images with the one ending in 52 as the background image because it seemed to have the most detail across the rock wall. I added a curves layer to each IR image, used the auto button to increase contrast in L. The a and b channels seemed to have less useful information, so I made each layer monochrome with a BW adjustment. Here is how I used the IR layers:

             Image ending in 52 is background layer.

Image ending in 45, added in multiply mode, blend-if to keep changes to mid-tone since most of the figures were mid-tone greys.

[Image ending in 46, no improvement in figure definition, so not used]

Image ending in 47, added in screen mode with black mask, mask painted white along top and right edge of image to bring out detail in the rocks.

[Image ending in 48: no improvement in figure definition, so not used]

Image ending in 49: added in multiply mode with black mask; painted with white brush (with brush in overlay mode) onto the figures to bring out details especially of those in the left and middle areas.

[Image ending in 51, no improvement in figure definition, so not used]

Above the IR layers, I added a curves adjustment layer in overlay mode with a mid-tones layer mask to concentrate adjustments mainly to the figures and using and blend-if to further protect lighter tones. I pulled the curve down to darken the figures, then put the curve layer into a group folder with a black mask. I then painted white on the group mask as needed to optimize the darker detail in wall figures without darkening the surrounding rock areas and without damaging the mid-tones mask inside the group (mask the mask echnique).


I then converted the Lab IR stack to sRGB (flattening in the process).


Using the flat original ending in 44 as a new base layer, I placed the sRGB combined IR result as a new layer in luminosity mode. From there:

              Stamped layer, applied auto-tone with minimal change visible, so deleted the stamped layer.

              Added hue/saturation layer to boost color saturation.

              Made a stamped layer and sharpened with Topaz Sharpen AI.

              Exported as jpg.


I see by comparison to other submissions that mine could have used more color. I found the challenge useful in that it made me think hard about ways of using the IR images to extract detail, quite different than a typical color correction task. Am looking forward to hearing how others produced their submissions.

Robert Wheeler

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