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Help with Colour tinge


12 Dec 2011 12:13AM
Hi,

From the outset I am aware what my mistake was and I know not to make a similar one in the future.

Earlier this year I bought some cheap ND filters so that I could experiment with them and try out some new techniques. One of the the things I have discovered is that as they are cheap they can tinge the picture that I have taken with a red / blue / purple colour.

My question is how should I adjust this so the colour is back to normal. I presume that there may be a way of comparing colour in a test image taken without the filters on and with the image taken using the filters so that the one can be matched to the other? Please can someone guide me through the process I should use, or point me in the right direction?

I have Photoshop CS2, Lightroom 3.5.

Many thanks for your assistance,

Rob

PS I know I shouldn't have bought cheap filters and should have saved up for decent ones but I wanted to experiment!

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12 Dec 2011 12:31AM
Look for "Colour Variations" in your software. Any colour casts can be worked on there.
GlennH 9 1.9k 1 France
12 Dec 2011 7:13AM
In Lightroom use the white balance tool and select an area of the image that you think should be neutral, and then click.

You can do a similar thing in Photoshop by using the middle eye-dropper in levels or curves and clicking on an area that you think should be neutral grey. Or if you want to be more precise:

1/ Open the info palette
2/ Using eye-dropper tool, shift-click on an area or areas you think should be neutral to create sample points (for example, an area of white cloud). Set the eye-dropper tool to take a 5x5 or 11 x 11 sample.
3/ These samples are recorded in the form of sets of RGB numbers on the info palette. Neutral colours should have equal RGB co-ordinates (e.g. neutral grey is 128, 128, 128).
4/ Using the curves tool, adjust each RGB channel individually so that the RGB numbers in your sample points are equal, or close to equal.
5/ Remove sample points (shift/alt and hover over them to click)

This works well for straightforward colour casts, although obviously ordinarily you wouldn't want to 'neutralise' every picture.
User_Removed 5 4.6k 1 Scotland
12 Dec 2011 9:14AM
It is not so much about the "cheapness" of ND filters. Some of the 3 ones from China are the purest in terms of neutrality whereas some of the expensive ones are reputedly quite bad. You may have noticed on the Forum that people either swear by Lee of swear at them.

As mentioned above, Lightroom provides the perfect solution. Create user presets for each filter if you use them a lot and want to save "correction time".
Nick_w e2
7 4.1k 99 England
12 Dec 2011 9:30AM
If the filters are grads, it's very difficult to colour correct fully. It only affects the top half of the image and then it graduated.

It's often referred to as a colour caste, but it's not really, the pigments used to make the grad are good at blocking visable light - but not IR. the longer the exposure the more IR is let through.

This manifests itself as a brownish/ purple colour. To make things more complicated folliage in the area of the graded part of the filter will come out almost white.

The above methods mentioned above are great for conventional colour correction work. And they do work to a limited degree with cheap grads, but will not correct every image adequately.

One of the reasons the likes of LEE are expensive is they use a combination of pigments / IR blocking coatings ( which are very expensive - hence the price differential).
18 Dec 2011 11:22PM
Thank you all for your comments and assistance, now just need the time to sit at the pc and see if I can make a picture look half decent.

Rob
User_Removed 5 4.6k 1 Scotland
19 Dec 2011 11:30AM

Quote:
It's often referred to as a colour caste.




I hope not. Racism will not be tolerated on this forum!


Tongue

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