Image Value Remapping
I’ve finally got around to finishing pretty comprehensive support for “remapping” pixel values from images within my image-processing infrastructure, so as to be able to scale or remap pixel values in an image to another representation.
It supports both ‘linear scalar’ scaling, as well as scalar-to-colour (i.e. to an HSV gradient ramp) and scalar to custom configurable colour gradients,
in addition to being able to do additional pre-remapping scale and fit value modifications - i.e. re-fitting values from a data value input range of [-5000.0, 20000.0] to [0.0, 1.0] first and then applying scalar-to-colour gradient remapping afterwards.
This was mainly for two particular use-cases I had: the first was some more map visualisations I’m playing with - in particular some data on Global Shipping Traffic Density from the World Bank, where I got a bit frustrated with QGIS’s gradient-remapping functionality, so decided to roll my own in order to allow it to be more recipe-based with configurable parameters and then allow remapping multiple images with exactly the same params more easily.
Below is an example of remapped Global Shipping Traffic Density around Europe, with the reprojected (in terms of map projection) absolute values from the source file data being remapped to a custom colour gradient output image:
The second use-case was remapping 8-bit greyscale values in JPEG files taken from a thermal camera I’ve had for a while, to be able to remap them to more interesting and configurable colour gradients.
Original thermal camera image:
Remapped image:
Original thermal camera image:
Remapped image:
The thermal camera I have does support some colour gradient automatic remapping itself, however there are only 8 presets, and the result is baked into the captured JPEG image, so having the flexibility to capture in greyscale in the camera and then remap the images later is much more useful.
I do have some older interesting images I captured just after getting the camera years ago, where I was mostly capturing the images in pre-baked gradient format, which I would like to change the gradient of - so a possible feature improvement to my image-processing infrastructure might be to add support for “reverse-mapping” the colours in images from a gradient back to a “scalar” or linear value, so I could then apply custom colour gradients of my choosing.