Re: [Gimp-user] Colour Correction In Camera Trap Images

["Rick Strong" <rnstrong primus ca>]

I am not a colour  expert but I am an amateur photographer and have worked 
with Landsat images (from B&W false colour positives).

The problem of not altering the original image is simply solved: just work 
on duplicates.

There is only one "standard" that I know of and that's a  grey scale card 
(15% grey, I think). If you have that in each photo you should have a 
constant grey scale reference. This will allow you to relate differing eye 
colours to the known ages of the Goshawks.

If you have the same grey card reference (or a similar one) in each leg shot 
you can also relate the leg colours to the known ages of the birds. This, as 
I understand it, is what you are trying to do.

Again, if I understand you correctly, you are looking for an 
algorithm/equation that when applied to a sampling of grey card pixels will 
convert that grey card to the corrected colour and so, one hopes, that the 
same algorithm/equation applied to a sampling of Goshawk eye or leg colours 
will return them to standard, relateable colours. BTW, I trust the camera 
captures images in a high DPI so that you have enough pixels to work with.

I trust I have described your problem correctly. In any case, I don't know 
what that algorithm/equation is, however I seem to recall one of the GIMP 
developers is a Colour conversion specialist. Would her name be El? Sorry I 
can't be of more help. Maybe someone else can chime in or create a batch 
macro.

Go Goshawks!
Rick


-----Original Message----- 
From: AUGUST, KATHERINE (PGR) via gimp-user-list
Sent: Monday, November 29, 2021 4:54 PM
To: gimp-user-list gnome org
Subject: [Gimp-user] Colour Correction In Camera Trap Images

Hello,

I am a PhD student at the University of Aberdeen, Scotland. My work is 
looking at the population dynamics of goshawks, a forest specialist bird of 
prey, in the northern UK. As part of the monitoring, I use camera traps to 
get images of individual goshawks. I now wish to compare the eye colour of 
known age individuals to see if I can determine a relationship between eye 
colour and age (goshawk eyes start pale yellow and become redder with age, 
but this has never been quantified before).

In the camera setup, I include a greyscale chart to act as a colour standard 
as images are taken in a variety of lightings. I also wish to determine if 
the goshawk leg is a consistent enough colour that it could be used as a 
standard.

I am using GIMP to get the pixel RGB values for the eye, leg and various 
greyscale squares. I feed this into a dataset and would like to use the 
different colour standards to correct the eye colour. This would then allow 
me to compare the repeatability of the various standards across images of 
the same individual. From speaking to amateur photographers, I believe the 
usual method would be to correct the image within GIMP, but as I want to use 
multiple colour standards, I would prefer not to alter the image itself.

As it can be done within GIMP, I am assuming there is already some kind of 
conversion algorithm/equation for doing the colour correction. So, my query 
is, what is this conversion equation?

Any help would be greatly appreciated and appropriately recognised!

Thank you,

Katie

Katherine August
PhD Researcher NERC Case Partnership

University of Aberdeen
Room 422 Zoology Building
Tillydrone Avenue
Aberdeen
AB24 2TZ
Email: k august 18 abdn ac uk<mailto:k august 18 abdn ac uk>

While I may be sending this email outside of my normal office hours, I have 
no expectation to receive a reply outside of yours.



The University of Aberdeen is a charity registered in Scotland, No SC013683.
Tha Oilthigh Obar Dheathain na charthannas cl?raichte ann an Alba, ?ir. 
SC013683.