Idaho Airships, Inc.

We’re continuing our development of a resolution for haze, specifically targeted at oblique aerial images using Layers and Blending Modes.

The Hard 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.

Hard Light calculates the per-Channel Blend Layer values to 0 (black) through 1. This obviously involves some translation from the bitwise. Please see The Soft Light Blending Mode for a more fundamental explanation.

Symbology:

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

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

A = 1 – (1 – C) * (1 – B)

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

A = B * C

It just so happens that the first formula above is the machinery for the Screen Blending Mode, and the second is that for the Multiply Blending Mode-we have picked up 3 Blending Modes for the investigative cost of two. The neutral color of the Contrast Group Modes (Soft Light, Hard Light, et. al.) is gray, while the neutral color of the Lightening Group constituent (Screen) is black, and the neutral color of the Darkening Group constituent (Multiply) is white. The neutral colors of the Screen and Multiply Blending Modes are never really a factor since each of them is confined to the opposite side of the effect threshold: Screen to the higher luminance range (away from Black) and Multiply to the lower luminance range (away from White).

If the Blend Color is the neutral color of the Blending Mode, it has no effect on the Background Color-we’ll often use a Fill Layer of the Blending Mode’s neutral color as the Blend Layer, and paint upon it to effect the desired change to the Background or target Image Layer. That’s a good strategy since such a Layer is easily modified and/or duplicated with no destructive effect on the target Image Layer.

Hard Light, as the name implies, produces Contrast more aggressively than Soft Light. Cursory investigation of the math shows that Hard Light will in fact introduce clipping given a Blend Color extreme of 0 or 1-thus, Hard Light should be used with the caveat that the Blend Color (or another parameter such as Layer Opacity) must be moderated if clipping is to be avoided.

Hard Light is also effective at introducing compensatory bias by simply biasing the Blend Color.

With the combination of Soft Light and Hard Light Blending Modes we have a pair of fully programmable tools with which to resolve insufficient or defective (biased) Contrast via the preferred method of Adjustment Layers.

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