Colour casts

It is obvious with my degree of Red Green colour blindness that I am un able to detect certain colour casts- especially green. Of course I can see greens but its the subtle shades that are the problem.
I have just "aquired " a copy of Photoshop 7.
Quck question- is there any way photo shop will find a colour cast and cure it. - WITHOUT me suggesting there is one and doing it manually?
I can't suggest one or try it manually as I may not be able to tell if there is one in the first one..
Thanks
JohnR

If you just hover the curser over various parts of the image and look at the Info pallette, it will tell you exactly what the R, G and B values are. You can then adjust them using your preferred method, i.e. curves, etc.

If you us the eyedropper in the levels tool to set whites, mid-tones and blacks it should eliminate a color cast unless you want that cast there i.e. a 'warm' picture

Hi John,
I too suffer from colour blindness, in my case I can't tell brown from green nor pink from blue, but I can always see a colour cast in a photo...figure that one out all you ophthalmologists out there.... although telling what colour the cast is isn't a strong point.

All these rgb dropper cures that are bandied about are great for those who know where a mid tone is, but for the colour blind they are a non starter, colour by numbers does not work if you don't know what the colour the number represents should look like

Tom, isn't your levels trick is pretty much what most digital cameras do in AWB and most do it poorly (even the new mk4, which imho does it worse than the old mk2)

John, the only get out is to ask the wife (or anyone else who might show an interest)

Absolutely John.!
Its not that simple if you don't see the cast in the first place
I did the dropper trick on several areas of blacks and got completely different readings every time. Is it all worth it !
The other thing is , as you well know,that Corvids, Starlings etc have a great deal of green in parts of the plumage anyway !! Iridescent it may be.

Cheers
John

Make sure in levels that the RG and B drop downs are ok, I check each one individually and pull the sliders in if necessary-hope that makes sense

Dave

Ah sure you were having us all on ----------- HAPPY ST PATRICKS DAY

John , I also have problems from time to time , evidently my results can show a purple or magenta cast , my eyes seem to play tricks when I’m tired , which now seems much of the time. I have a book on PS written by Martin Evening, it’s said to be the bible on PS, others may disagree. In the book he sets out the following method:

Go to Image- Adjustments-Threshold- this opens a black and white histogram. Slid the slider to the left until the last trace of black is showing, hold down the left hand mouse button and drag the eye dropper over the last trace of black. Holding down the shift key click the mouse this will leave a marker at that spot. Next repeat the process for the white side by sliding the slider to the right and repeat the process. DO NOT OK THIS BUT PRESS CANCEL.
Next go to Levels and take the white eye proper and click on the mark that you made on the white spot , then take the black slider and click on the black spot . Finally take the middle grey eye dropper and try to find neutral grey , open the Info on the right hand side of the screen , the trick is to get the RGB numbers in the top left of the Info box all reading as close to the same value as possible.
It sound very involved but in practice it only takes a few minutes. It doesn’t work 100% of the time but most of the time it gets it close enough for personal preferences to be applied. I tried it on you Ravens and it looks fine but with my eyes it may have a purple cast !!!!!!!!!!!. Hope this helps.

Bob.

Thanks everyone.
I,ve tried the suggestions and it works !!
Fancy having tio use photoshop though
Will still use PSP for the other stuff though !
Thanks again
JohnR

I tried this method a long time ago, and yes, it works nicely, but, not being a photoshop guru, i can never get rid of the markers it leaves on the image. I just use the info box, the same as Bob uses for finding a mid-tone, but for the blacks (0,0,0 ) and whites ( 255,255,255 ) , seems to work fine, but as with anything, it wont work all the time. I save time now, having made a strip of 3 small boxes, black ( 0,0,0 ), mid-grey ( 127,127,127 ), and white ( 255,255,255 ) I open this, and keep it open in photoshop, then use the droppers in levels on this. Most of the time, once the blacks and whites are set, the mid-tones fall into place.

All good advice, but don't lose sight of the fact that frequently we do not want white to be white esecially when shooting around the golden hours - white is often tinged orange/ red or picks up the blue sky so can naturally have all sorts of colour casts really......

It must have been really easy in film, photographers have to be so much better these days. (irony )