removing colour cast

probably done before but what is the easiest method of removing colour cast that comes from nd filters, magenta usually, at least with cokin and hitech.
thanks in advance for any replies

Convert it to B&W. Not a flippant reply, I'd like to know too.

You don't say whether this involves an ND grad, but I guess it does, since that's the most difficult case. You'll need a package which allows you to apply a graduated tint to the image (like ND grad in software - which Lightroom does).

Basically it would have to be a layer which matches the "ND to full transparency" transition point of the original filter, including whether it was a hard or soft grad.

What you'd then want to do is to apply a green(-ish) tint to the layer (to counteract the magenta cast). Ideally you'd want to measure the degree of cast first (using a known neutral object in the ND zone) so you could see how much cast you were trying to remove and whether it was green channel only that was "down" or whether other colours were also affected.

Sorry I can't be more precise but it also depends on what software package you're using for post processing. I know exactly how I'd do it in Lightroom but if you're using something else that won't help!

Paul

You could try using the remove colour cast tool in photoshop or PSE; or, to simply remove magenta tones, you could select the adjust hue/saturation tool, pick 'magentas' and wind back the saturation. Obviously you may need to do some nifty work with layers or similar in the second case if there are things in the picture which are supposed to be magenta...

In Photoshop CS and later, Photo Filters might be an easy route. Just dial in the appropriate amopunt of colour compensating filter.

In Lightroom you can easily alter the saturation of red, orange, yellow, green, aqua, blue, purple, magenta separately via the appropriate sliders

first thanks for the responses. i use pse8 and in answer to Paul it,s both grads and full. grads not usually a problem unless stacking to get5 or 6 stops ,the hitech 10 stop is the worst just get a beautiful magenta photo, with the software i have it looks like gareth may have the answer. the other option for the 10 stop i was thinking of perhaps the b&w 110 as i probably would only use it on the 16-45
thanks once again

What software do you've?
if you've photoshop i've another option that you can use.

Duplicate the layer and use the filter average blur.
The layer will be on tone, it's the average colour of your photo.
Now open a levels or curves as a layer adjustment and use the middle grey sampler on the average blured layer, it will make the average grey.
Now hide the averaged blured layer and the cast should be removed in your photo.