Flatfield calibration doesn't correct RGB channels individually

[sschmaus]

Expected Behavior

Calibrating a HELI_RTE image should perform a flatfield calibration that removes the color gradient in the original images. I modelled the RTE flat V3 with slightly different gradients per channel, so the apparent color cast can be corrected.

This is how it should look like (per channel calculation of RTE_IMAGE*mean(RTE_FLAT)/RTE_FLAT)

Actual Behavior

Currently MRU appears to calibrate all channels with the same flat values. It appears to use either just one of the flatframe RGB channels or a greyscale version of the flatframe. Therefore the luminance gradient is corrected, but a color gradient remains.

This calibration has worked correctly in the past, I first noticed this issue with versions after the switch to sciimg.

This is the output from MRU:

Steps to Reproduce the Problem

1. calibrate image with m20_hrte_calibrate -i *.png

Possible Solution

Perform the flatfield correction on every channel individually and with the corresponding flatframe channel. i.e: R: RTE_IMAGE_R*mean(RTE_FLAT_R)/RTE_FLAT_R G: RTE_IMAGE_G*mean(RTE_FLAT_G)/RTE_FLAT_G B: RTE_IMAGE_B*mean(RTE_FLAT_B)/RTE_FLAT_B

Specifications

• Version: 0.3.3
• Platform: Windows

• Subsystem: native

  also tested with a slightly older version of MRU in WSL2/Ubuntu 20.04 on Windows

[kmgill]

Issue is in sciimg submodule in rgbimage.rs, line 330, which only ever grabs band 0 from the flat. I'll fix that by adding a check for additional bands (not assuming three channel RGB or single channel monochrome)

[kmgill]

For reference: https://github.com/kmgill/sciimg

[kmgill]

Fixed with update to sciimg. Update to Cargo.toml for updated sciimg version number. Reference: https://github.com/kmgill/sciimg/commit/25cf445f4532e0439c174083b21b8b9cccc00537