Texture Scaler is a seemingly boring but quite useful utility program which allows height maps to be rescaled. The height map is mapped to the specified range. The original range is considered to be 0 to 1 if the Pre-Scale Heights to Entire Range option is disabled, and the minimum height to the maximum height within the selected portion (actually its bounding rectangle) of the image if the option's enabled. The Feather Far Pixels option is useful for erasing the zero-height background when combing height maps using the Texture Merger with the Minimum merge method. Unchecking the Produce 24-Bit Height Map option allows it to be used to scale grayscale height maps (and other grayscale images too, I suppose).
Here is the plugin (version 1.2.6431.28257): TextureScaler.zip
From the Help Menu:
Texture Scaler scales a height map to a specified range.
The controls are:
Pre-Scale Heights to Entire Range: When enabled, the height range is adjusted prior to scaling so that the minimum pixel height is zero and the maximum pixel height is one. Equivalently, the minimum height will be mapped to Minimum Height and the maximum height will be mapped to Maximum Height. When there is an active selection, the pixels within the selection's bounding box will be used to determine the depth range.
Set Transparent-Pixel Heights to Zero Before Scaling: When enabled, the heights of transparent pixels will be set to zero before mapping to the final range. Equivalently, transparent pixels will be mapped to Minimum Height.
Don't Scale Transparent Pixels: When enabled, the heights of transparent pixels are not modified by pre-scaling or by the range scaling. If this option and Set Transparent-Pixel Heights to Zero Before Scaling are both enabled, the heights of transparent pixels are set to zero.
Feather Far Pixels: When enabled, the transparency of scaled pixels near the Minimum Height will be increased.
Feather Range: Specifies the proportion of the Minimum Height to Maximum Height range that will be feathered when Feather Far Pixels is enabled. When Feather Range is zero, pixels at the Minimum Height are fully transparent and all other pixels are unmodified. When Feather Range is one, the pixel transparency will decrease linearly through the full height range.
Produce 24-Bit Height Map: When enabled, the scaled height map will have 24-bits of precision. When disabled, the scaled height map will be an 8-bit grayscale image.
Minimum Height: Specifies the minimum value for the scaled height map.
Maximum Height: Specifies the maximum value for the scaled height map.
The user interface:
EDIT: Version 1.1. Replaced buggy version. Increased slider precision from 2 to 3 places.
EDIT 8/9/2017: Version 1.2. Fixed various bugs; added "Don't Scale Transparent Pixels" control; Modified feathering control.
EDIT 8/10/2017: Version 1.2.6431.28257. Minor change to avoid unlikely problem.