Correcting colour casts from ten-stop filters

ianmarsh

ianmarsh

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I took a bunch of photos of the Shard a few days ago, each with a ten-stop filter in place. I also took a non-10-stop shot of more or less the same scene. While I quite like the colour cast effect from the 10-stop I'd like to be able to get rid of it, at least for other situations.

Is there a robust and hopefully easy way of getting the ten-stop colours closer to the non-ten stop ones? I have Lr and Photoshop CC. I have tried moving the HSL sliders around in Lr but that is too hit and miss and I usually end up in a worse position than I started.
 
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I got myself a grey card for my wallet. It has
the same size and format than a credit card.

Take a shot of it in the frame with the ND fil-
ter and correct in PP. Have a good time! :cool:
 
I think the line "and correct in PP" is where I am looking for help! I keep forgetting to use a grey card but I should learn. For now though, I have two images, and I want to know how to get the colours in one closer to the other
 
Is there nothing in your photo which is pretty close to white or grey so you could use it as a WB reference in your post-processing? Such as a white or grey cloud, a road sign, a grey painted street lamp pole, etc.? Generally speaking auto WB should get you pretty close to it as well, provided you're either editing a JPEG or using a RAW editor which pays attention to the WB parameters set in the EXIF data from your camera.
 
ianmarsh said:
I think the line "and correct in PP" is where I am looking for help!
Click to expand...


WB is the less critical parameter at SR. Include the card
in a shot and use the WB picker of you software. :cool:
 
Rather than use HSL, use the White Balance. Don't know which 10 stopper you are using but the Lee ones tend to make images more blue, so warming the image up is the way to get nearer to "natural" colours. The type that give a magenta cast will probably need warming up too and then the tint moved towards green.
 
May, or may not work.... If you have a grey card (digital grey card, not a kodak 18% grey card) then take an image of it with your filter on, correct that image for wb and apply the same correction to your Shard image, as I say it may or may not work but I think any cast will be consistent.
 
In the shots I am using have a decent grey bit, so that would give a reasonable starting point, but I have others of Icelandic waterfalls where I have blue-ish sky, green-ish grass and water that looks red due to the cast. I can get a couple of the colours to look reasonable, but not all three by tweaking the WB.

I think what I am after is a technique where I can choose each colour in the normal shot and make the same area of the ten-stop shot look that same colour. The WB way might be a good start but I am with Phil that it doesn't seem perfect. I suppose a colour checker is possible in future but I am also looking to go back into my catalogue.
 
ianmarsh said:
In the shots I am using have a decent grey bit, so that would give a reasonable starting point, but I have others of Icelandic waterfalls where I have blue-ish sky, green-ish grass and water that looks red due to the cast. I can get a couple of the colours to look reasonable, but not all three by tweaking the WB.

I think what I am after is a technique where I can choose each colour in the normal shot and make the same area of the ten-stop shot look that same colour. The WB way might be a good start but I am with Phil that it doesn't seem perfect. I suppose a colour checker is possible in future but I am also looking to go back into my catalogue.
Click to expand...

I tend to find with the Nikon Cameras the default cloudy setting is a good WB for non filtered images and with the little stopper the one that's one preset warmer spits out RAWs that have a similar colour match to the unfiltered cloudy ones.

I fine tune all my wb's and tints in post, just get an approximate one in camera is all thats needed
 
What @Kodiak Qc and @PhilH04 are correctly suggesting but not completely explaining is this.

With a known neutral colour, best to use a grey card under controlled lighting or ideally daylight take a shot with the cameras white balance set to daylight (not AWB). Add the filter and with it still set to daylight white balance take another shot.

Take these 2 raw files into your raw converter. looking at the non filter shot first. Use the white balance colour picker to correct the grey of the card to neutral grey. Make a note of the kelvin numbers and tint.

Open the one with the filter, repeat the process.

The custom white balance for the first one will give different kelvin numbers and tint to the custom white balance of the second.

Assuming a blue tint to the filter take off the kelvin value of the first one from the kelvin value of the second. For example 8900k - 5400k = 3500k. Do the same for the tint, make sure you go the right way.

You now know the colour cast of the filter, so if you have no problems getting the non filtered shots accurate regarding white balance, or if the awb is good, just add in the 3500k (in this example) to correct the filter cast.

The short version is to remember the original kelvin and tint of the corrected filter shot and use this as your daylight starting point for use with the filter. But that is only if your non filter one did not require any correction. If that also required + 300k pretend, then reduce that from the corrected with filter numbers to give you an accurate starting daylight point.
 
Craig_85 said:
What @Kodiak Qc and @PhilH04 are correctly suggesting but not completely explaining is this.

With a known neutral colour, best to use a grey card under controlled lighting or ideally daylight take a shot with the cameras white balance set to daylight (not AWB). Add the filter and with it still set to daylight white balance take another shot.

Take these 2 raw files into your raw converter. looking at the non filter shot first. Use the white balance colour picker to correct the grey of the card to neutral grey. Make a note of the kelvin numbers and tint.

Open the one with the filter, repeat the process.

The custom white balance for the first one will give different kelvin numbers and tint to the custom white balance of the second.

Assuming a blue tint to the filter take off the kelvin value of the first one from the kelvin value of the second. For example 8900k - 5400k = 3500k. Do the same for the tint, make sure you go the right way.

You now know the colour cast of the filter, so if you have no problems getting the non filtered shots accurate regarding white balance, or if the awb is good, just add in the 3500k (in this example) to correct the filter cast.

The short version is to remember the original kelvin and tint of the corrected filter shot and use this as your daylight starting point for use with the filter. But that is only if your non filter one did not require any correction. If that also required + 300k pretend, then reduce that from the corrected with filter numbers to give you an accurate starting daylight point.
Click to expand...
or just copy and paste the settings from the non filter photo to the filter photo job done
..
 
ianmarsh said:
Thanks Craig that makes sense. And is the colour cast fixed in all situations or might the adjustment depend on the ambient light conditions of each shoot?
Click to expand...

It might depend, I've not actually tested it that in depth. I suppose it depends if it is the colour of the glass you are correcting for, in which case it's fixed regardless of ambient. Or if the darker glass cuts out different wavelengths of light unevenly, in which case it will vary under different lighting.

That's why I feel doing it in at close to daylight white balance conditions is a balanced middle ground. If you know at that setting you need an extra 3000k and 5 magenta tint, it's a good starting point to add to a non filtered shade white balance scene...
 
Use a grey card in first image, Open all images in camera raw. Select all.
Click wb tool on grey card and it will be applied to all images selected.
 
If you make a copy layer in PS then apply a Blur/Average the open a adjustment layer /curves. Take the mid gray eye dropper and click onto the blurred layer after this hide the blurred layer you should have removed the colour cast, if its too strong adjust the opacity of the curver layer then flatten.
 
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