Beginner level projection Options

[Brian Swift]

Anyone have any good advice on scaling the RGB to give the closest to true color? I tried these two [0.487, 0.408, 0.172] [0.444, 0.341, 0.155] from Brian's flow and I get a strong orange hue.

My colorBalance values specify the upper end of the range of the input components, so you'd divide by them.
When rescaled, they are similar to Bjorn's.
1/colorBalance/Min[1/colorBalance] = {1., 1.193, 2.8378}

[Brian Swift]

I usually multiply by [1, 1.12, 2.3] after decompanding. I'm surprised that [1, 1, 0.95] seemed close - are you decompanding the images before applying these?

I've been wondering, is your natural color process more involved than a scaling?
And also how you derived your color balance values?

My current (too blue) values come from the median of my flat fields. Early on they came from the max values from an image of Europa.

[adamg]

Sounds like I'm miles off for some reason. I used the RDR product assuming it had already been decompanded, I recall I have a range to 4kish so it has certainly been through something.

[fredk]

I've been wondering, is your natural color process more involved than a scaling?
And also how you derived your color balance values?

In particular, shouldn't a colour space matrix transformation to, eg, sRGB be performed from the raw colour channels? That generally can't be approximated by a simple scaling of each channel.

[adamg]

The RDR data set says "For planetary targets, these values are then scaled such that a white surface at the solar distance at the time of imaging and with the commanded exposure time would have a pixel value of 10,000 data numbers.", so I'm assuming the blue already got scaled before I got to it. I probably ought to use the EDR data set if I want to actually know how it got scaled.

Regarding sRGB, it seems sensible to me that you can scale the linear raw IMG which is what I'm doing but should I be trasforming to sRGB at some point?

[mcaplinger]

The RDR data set says "For planetary targets, these values are then scaled such that a white surface at the solar distance at the time of imaging and with the commanded exposure time would have a pixel value of 10,000 data numbers."

Well, I wrote that, and I don't know how to make it any clearer than that.

"Natural color" requires you to model the human eye response. The Junocam RGB filters are not much like the human eye response (unlike the Bayer pattern used for MSL) so one would have to do something, but I'm not sure what.

In case you care, the EDR-RDR scaling code (after decompanding) is

CODE

ref = [111, 4766, 10331, 12669] # ch4, blue, green, red
scale = 16.3
sunrange /= 1.5e8 # km to AU
ex = float(i.info["exposure"])*int(i.info["tdi"])

dnout = int(dn*scale/ex/(ref[f]*(5.2)**2/sunrange**2)*10000)

[Brian Swift]

Regarding sRGB, it seems sensible to me that you can scale the linear raw IMG which is what I'm doing but should I be trasforming to sRGB at some point?

My colorBalance scaling is applied to decompanded raw non-calibrated image values. I usually use the "raw" files from the missionjuno.swri.edu, but
have also used PDS EDR files. I haven't worked with the RDR files.

I don't apply a linear to sRGB conversion unless I want to produce a natural-ish contrast image. Not performing the linear to sRGB makes the files from my pipeline display with more contrast.

[adamg]

Interesting, [1,1.23,2.66] I actually dropped my 0.95 so I think you nailed it.

mcaplinger, sorry I didn't spot your name on the technical report, that was pretty lazy of me! Congratulations on such a successful piece of hardware, as an electronics guy it's the camera itself that's got me interested, I've been very impressed.

[Brian Swift]

...as an electronics guy it's the camera itself that's got me interested, I've been very impressed.

Mike will correct me if I'm wrong, but I believe this is the hardware info for the CCD https://www.onsemi.com/pub/Collateral/KAI-2020-D.PDF

This and various other JunoCam reference links are at the top of the Juno24u notebook on GitHub.