Idaho Airships, Inc.

The Soft Light Blending Mode is an asymmetrical application that meters and applies on a per-Channel basis. Some potential for the introduction of bias exists in situations where one or two Color Channels are situated on one side of the effect threshold (.5) while the other/s are situated diametrically.

Soft Light calculates the per-Channel Blend Layer values to 0 (black) through 1. This obviously involves some translation from the bitwise. If the Blend Layer Channel (R, G, or B) value is >.5 (128+), the Base Layer Channel is modulated via negative Gamma (you’ve read our Gamma post?), meaning that it is darkened. If the Blend Layer Channel value is <= .5 (0-127), the Base Layer Channel is modulated via positive Gamma, or lightened. That’s why I use the descriptor “asymmetrical.”

To be absolutely accurate, the adjustment isn’t really “Gamma”-it’s not purely exponential, but the effect is very similar-enough so to be a little sloppy in our taxonomy just for the sake of proving I’m not a slave to mathematical protocol…which I understand makes me very cool?

Symbology:

• Resulting Color = A
• Blend Color = B
• Background Color = C

If the Blend Layer Channel value exceeds .5, the application per Channel is:

A = (2B – 1) * (SQRT(C) – C) +C

If the Blend Layer Channel value <= .5, the application per Channel is:

A = (2B – 1) * (C – C^2) + C

This calculation will limit the “Gamma” change to between .5 and 2, and will not force any aggregate mean or Channel value to the margins (0 or 1).

“.5″ (127 average of R, G & B) is the “effect threshold” mentioned in the first paragraph.

What you have experienced is for the aerial photographer what E = mc^2 was to Einstein-it unlocks an entire universe of potential for resolving some of our greatest enigmas.

In this case (relative to aerial photography), we have a tool that increases contrast with minimal uncommanded bias, and will not clip.

L