Saturday, September 27, 2014

3 IR Channel Swaps - Comparing Photoshop Channel Mixer, CNX2 Hue Swap, & Photoshop LAB Color

In my previous post, I demonstrated how to perform a LAB color channel swap and discussed some of the workflow advantages associated with this approach. However, the unresolved question is whether the LAB color channel swap provides a different photographic output than the better-known channel swap procedures.  

For this post, I will take the same TIFF image through the Photoshop channel mixer swap, the Nikon Capture NX2 (CNX2) hue shift, and the LAB color channel swap using the Curves function.  
Image 1. Starting Point - Out of camera TIFF image.
Image 1 is the out-of-camera image.  It was taken into CNX2 honor the camera settings and to set the WB. The image was then converted to a 16-bit TIFF to standardize all the inputs. Photoshop handles NEF files differently than CNX2 so this levels the playing field. All of the channel swaps started with this image.
Image 2.  Photoshop Channel Mixer Channel Swap.

Image 2 shows the standard channel swap procedure in Photoshop. This procedure uses the Photoshop channel mixer to swap the red and blue channels. The resulting image was saved as a JPG and displayed here. No other manipulations were performed. The image has a teal-like hue to the sky and the water and the upper foliage has a magenta cast.

Image 3.  Hue shift using Nikon Capture NX2.
Image 3 shows the hue shift from CNX2. The sky and water are blue in this image and the foliage has a green-yellow cast.

Image 4 shows the LAB color swap output.  This image most closely resembles the Nikon CNX2 hue shift output. The colors in this image appear to be darker or more saturated than the CNX2 output, but the difference is minimal.  

Image 4. LAB color swap with Curves.
To the purist, the CNX2 resemblance may indicate that the LAB color swap might not be a true channel swap.  As a pragmatic photographer, I really don't care whether the channel swap is "true" or not.  I just want the sky to be blue and to generate an image I can work with. After all, all IR colors are false colors and it really doesn't matter how we get to the final image. The true power of IR photography is that there is no "right" and "wrong" way to approach or depict an IR scene.  We are free to follow our artistic inclinations.

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