Practical Color Calibration for Mars Surface Images

Abstract

A human being’s psychological state depends in part on the colors of the surroundings. One of the familiar effects related to this is alertness stimulated by bluish light of high color temperature and induced weariness by reddish low color temperature light such as evening sunlight.

Hence, creating images approximating the visual color experience human explorers would have standing on the surface of Mars is an important part of preparing for their first presence there.

A professional photographer on Earth uses the combination of two devices, a spectrophotometer and a standardized color reference target, to color ­calibrate the raw image data for recreating the visual experience a visitor would have when
standing in the location where a photo was taken.

Because neither of these devices has yet been taken to the surface of Mars, an alternative approach is needed to determine a basis for color calibrating Mars surface images.

This talk describes a practical approach to color calibrating Mars surface images taken in 1976 by the Viking Lander and images from 2012 until present taken by the Mars Curiosity Rover. As a distinctive feature, the presented approach works primarily using the spectral sensitivity functions (SSF) of the camera sensors and incorporates the non­standard color calibration targets on the Mars landers only as secondary input.

Full text

Practical Color Calibration
for Mars Surface Images
Holger Isenberg
http://areo.info
holger.isenberg@gmail.com
Mars Society Convention
Irvine CA, 9/2017
Image: Rosetta ESA MPS OSIRIS
Copyright © 2017 by Holger Isenberg. Published by The Mars Society with permission.

Which colors
would a human perceive
on the surface of Mars?

Which colors
does a human perceive
in different locations
on Earth?

Sydney, during the 2009 dust storm
Image: David McLeish
http://www.neatorama.com/2009/09/23/sydney-dust-storm

Automatic White Balance vs. Daylight Setting

Daylight Setting Daylight Setting
Automatic White Balance Automatic White Balance

Camera Profile:
Transforms Raw Camera Image into final product
apply
Camera Profile
.ICC file
Local Scene
Raw Camera Image
Final Calibrated Image
take
Photo

http://www.ludd.ltu.se/~torger/photography/camera-profiling.html
Creating a Camera Profile

MAHLI camera
Malin Space Science Systems
RGB Bayer Filter
on CCD Image Sensor
Images:
http://www.msss.com/operations
https://en.wikipedia.org/wiki/Bayer_filter

Test images with Curiosity Rover Cameras
ColorChecker24 reference target
Malin Space Science Systems https://photojournal.jpl.nasa.gov/catalog/PIA13281
https://photojournal.jpl.nasa.gov/catalog/PIA15286
Color Reference Target
on Curiosity Rover

●Reference Target: ColorChecker24
●Defined lightsource: NIST StdA
●Camera: MAHLI, Curiosity Rover
●Raw Image
●Software for creating a Camera profile:
https://www.ludd.ltu.se/~torger/dcamprof.html:
●Mars Surface images in raw format:
https://mars.nasa.gov/msl/multimedia/raw/
Creating a Mars Camera Profile: Ingredients

Creating a Mars Camera Profile: Process
●Linearize MAHL raw image:
convert refimage.jpg -compress none -gamma 0.8 refimage.tif
●Extract color data from photo of ColorChecker24
reference target:
scanin -v -p -dipn refimage.tif ColorChecker.cht cc24_ref.cie
●Create the camera profile:
dcamprof make-profile -i StdA -I D50 refimage.ti3 profile.icc
●Apply camera profile to Mars raw image:
convert -gamma 0.5 -profile profile.icc rawimage.jpg calimage.jpg
https://www.ludd.ltu.se/~torger/photography/camera-profiling.html
http://www.imagemagick.org/script/convert.php

Quality Report for Camera Profile
MAHLI, D50, from ColorChecker24 image

Curiosity Rover, MAHLI camera
raw image
Image: NASA / JPL / MSL 0825MH0003740010301621C00_DXXX

Curiosity Rover, MAHLI camera
profile applied = daylight setting
Image: NASA / JPL / MSL 0825MH0003740010301621C00_DXXX
Calibrated by Holger Isenberg

Curiosity Rover, MAHLI camera
profile applied & white balanced
Image: NASA / JPL / MSL 0825MH0003740010301621C00_DXXX
Calibrated by Holger Isenberg

White Point during Clear Sky on Mars & Earth
daylight setting white balanced

Earth-like colors on Mars
Sunlight like on Earth
Awesome result!
Need a 2nd opinion!

Viking Lander flight spare
National Air & Space Museum Image: Holger Isenberg
National Air & Space Museum Washington DC

Unknown Color Reference Target
Image taken by Viking Lander Camera

Creating a Camera Profile
from the Camera's Spectral Sensitivity Functions
No photo of reference target required!

Camera Profile from Spectral Sensitivity Functions
●Create a virtual raw camera image
of a ColorChecker24 reference target:
dcamprof make-target -i D50 -c ssf.json -p cc24 reftarget.ti3
●Calculate the camera profile from the virtual image:
dcamprof make-profile -c ssf.json -t acr reftarget.ti3 profile.icc
●Apply camera profile to Mars raw image:
convert -gamma 0.5 -profile profile.icc rawimage.jpg calimage.jpg
https://www.ludd.ltu.se/~torger/dcamprof.html#workflow_ssf
http://www.imagemagick.org/script/convert.php

Quality Report for Camera Profile
Viking Lander 1, Camera 2, D50, from SSF

Viking Lander 1, 1976
raw digital image

Viking Lander 1, 1976
Camera Profile applied
daylight setting

Viking Lander 1, 1976
Camera Profile applied
white balanced

Viking Lander 2, 1976
camera profile applied
daylight setting = white balanced, only 7% diff.

White Point during Clear Sky on Mars & Earth
daylight setting white balanced

raw images: NASA / JPL / Viking 12E018, David McLeish http://www.neatorama.com/2009/09/23/sydney-dust-storm
White Point during Dust Storm on Mars & Earth
daylight setting white balanced

2 Profile Creation Methods for MAHLI Camera
Barely visible differences
Profile from
Reference Target
Profile from Spectral Sensitivity
Functions (SSF)

Panorama by Damia Bouic
Raw images: NASA / JPL
http://www.db-prods.net/marsroversimages
http://redplanet.asu.edu/?p=6574
Curiosity Rover, Sol 613
daylight setting

Only imperceptible differences between:
3 Calibration Methods in clear sky conditions
●profile from ColorChecker24 photo
●profile from Spectral Sensitivity Functions
●application of white balance
2 Mars Missions
●Curiosity MAHLI 2012
●Viking Landers 1976, 4 cameras, 2 locations

Conclusions
●Same light conditions on Mars and Earth
under clear sky near noon.
●No White Balance necessary.
●Applying a daylight camera profile replicates
the experience a human observer would have.
●Mars colors are not alien.
Colors and light conditions
won't harm humans' well being.

Possible Error Sources
●straylight / background reflections in CC24 image
●light source measurement error for SSF
●software bug
●unusual non-continuous spectrum on Mars
Solutions for next Mars Rover
●take CC24 image in daylight with Mars camera
●take sample images in daylight with Mars camera
●place dust repelling ColorChecker24 on Mars
●white target visible for ChemCam Spectrometer

Practical Color Calibration
For Mars Surface Images
Holger Isenberg
areo.info
holger.isenberg@gmail.com
Image: Viking Lander 1, 1976
calibration by Holger Isenberg