Curvemeister Forum

On the Photoshop forum, I asked the question about removing Blue Cast from Underwater Photographs.
I  had read post from Mike Russell    >>>

I use (or have used)    Two techniques:
1) use channel mixer to move green or blue into the red channel, to get rid of the cyan cast.
2) use Image>Adjust>Hue/Sat to bump the saturation.
   
or

1) convert to Lab mode, pick something that should be gray, and set it's a and b values to zero to make it neutral.
2) move the magenta end of the a curve horizontally to straighten the curve,
3) make both the a and b curves steeper to add more color. being careful to keep your neutral points in the same place
4) adjust the Lightness curve to get more contrast, in particular a clean
black and white.
....

Mike added ....

I have greatly modified the technique since then - Photoshop's new advances seem to be mostly non color correction related. Of the two techniques, the channel mixer is still probably the best place to start. If you look at the individual channels, it is not unusual to see an almost entirely black red channel, so moving data from one or both of the other channels is a good starting point.

This is the sort of idea that people like to discuss on the forum - www.curvemeister.com/forum - you may want to post your question there too.

So hence the Q

Some color cast is inherent in underwater photos. 
I have learned that if you change the color completely many people do not like the results.

Close ups where the flash fails are certainly an exception.  If you post a sample image we might be able to take a few swings at it and see if we can remove the cast and describe what we have done...

Greg

The issue is I don't usually use flash .... as for example would not have enough coverage for a wreck, or would cause backscatter issue.

Can I post a sample pic here or do I need to put it on a hosting site and post a link?

Post it here...The limit is 300 KB in physical size.

Greg

Here are 2 sample of somewhat typical Cyan cast ... simply due to depth, where red light has been filtered out.

These are usually around 4 MB jpeg, downsized for this site.

Here is a link to a short video.
http://www.curvemeister.com/video/greg/Underwater1/Underwater1.html

Some things to think about....

You want some color cast to maintain the underwater "look"
The amount of Cast removal is up to you...This is highly subjective....

Greg

Greg .thnx for the video explanation, helped me follow what you were doing.
In the original the fins were actually almost the correct colour, while your correction made huge difference to overall shot, fins are now magenta?
Is there a simple way too correct that without losing the benefits the adjustments have given.

Let me think on that a bit...
I would create an inverted magenta channel mask at that point I think...

I'll test that and let you know.
Greg

OK instead use a b channel mask from LAB and invert it. as shown in shot 1 then adjust the b channel as shown in shot 2
This is a rough version done for speed..forgive any odd artifact in the image...
Greg

Impressed with result, could you explain that step a bit more?
This is new for me.