Help needed from photography/imaging experts about colour correction
Hi all,
I am currently undertaking a software project for university which helps blind people recognise colour. I point a webcam at a scene take a snap shot and pick out the object whose colour is being recognised.
Obviously a webcam gives poor colour compared to a digital camera which everyone here will be used to, but my major problem is lighting conditions which I am sure you will have all encountered.
To solve this I am trying a number of different methods including photographing different calibration targets prior to taking the actual photo. I have a target which has red green and blue on it and i also have a target which has black white and 18% grey on it.
Firstly I would like to know if there are any thoughts on these 2 methods of colour correction, and possibly if there are any more i could consider.
Secondly, and more importantly, I have been playing with the black white grey method in Adobe Photoshop CS2 to see what results it will give me. I used the curves tool and selected the black grey and white point on my target using the colour droppers. I then saved the curves files (ACV) and applied it to several photos I took straight after photographing the calibration target. The changes I saw ARE enough for what i need for my application.
So now I know that the method works, I need to know what is actually happening to the pixels or histogram of the image when applying this method, i.e. is the histogram being stretch in some way? I simply dont know the answer to this and I need to find out because I need to implement the technique in a programming language working only with each pixel and the image histogram.
I hope this is where the photography experts will come into their own.
As a final note I have a second Red Green Blue calibration target of which i know the RBG values; Red = 195,0,0 Blue = 0,0,195 Green = 0,196,0
I took an image of the target using the webcam and then used the dropper tool to work out the values for RGB in the actual image which were:
Red = 151,56,45
Green = 114,190,127
Blue = 61,91,183
How do I know alter the image so that the colours on the target within the image appear the exact colour they are supposed to be?
PS. Ive attached two examples of calibration targets so you can see what the exact (poor) quality im working with.
Thank you very much for your time, it is much appreciated.
Lee