Custom WB question

[davidc]

A while back, as part of my 365 Project, I experimented with a homemade ND10 filter -


10 Stopped - 217/365 by cedarsphoto, on Flickr

Though I like the outcome, colour cast included (it looks retro ) I've since bought another ND10 filter.

Reading online, the colour cast you get from these filters can often be so strong you can't correct it with raw processing alone - the image above proves that - and people have suggested setting a custom WB in camera, using it for your shot then tweaking in LR to get the "correct" white balance. I've never used a custom WB before so I have questions

I think the problem is this, illustrated by hypothetical argument & made up numbers. Let's say that the colour temperature & tint of the actual scene is 5000K and 0 respectively. i.e. sunlight, and "no tint". When I take a photo using the ND10 filter, it would record a temperature (for the sake of example) of 2000K and a tint of 10.

The RAW file processing in Lightroom has sliders that control tint & temperature, meaning I can correct it to produce the correct white balance. However, the sliders - again, for example - only allow a correction of +/- 2000K and a tint of +/- 8

So in this hypothetical example, the "best" white balance I can achieve is 4000K and a tint of 2 which is not therefore the true white balance I want to render.

My questions are -

1) If I set a custom WB, does it save it in a Canon SLR until I overwrite the custom WB or until I turn the camera off? I have a 550D so I suspect it's probably the same across most newer Canon bodies. Since I never use custom white balance, it would be handy to set it permanently to "ND10 mode" and never have to reset it for my ND10 exposures.

2) I didn't think the white balance data was applied to the raw file, it simply records the colour and luminance data that hits the sensor? So how would a custom WB affect it? How would a custom WB mean I can ultimately achieve a temp of 5000K and tint of 0 that I'm looking to get?

My assumption is that the white balance setting of the camera is factored into how the RAW file renders in Lightroom but it can be overridden. When I import, it will have pulled the white balance back into the region where I can tweak sliders to get a "true" rendition.

Does any of that even make sense?

[Mike Farley]

I have a similar issue with my infrared photography. Left to its own devices, the camera will record an image with a marked red hue which is not very helpful when assessing the result on the rear screen. I overcome this with a custom WB in camera, but Adobe Camera Raw simply ignores it and I have the overly red image again. Other than making the image harder to view, it's not an issue if I am converting to mono, but it creates havoc if I want to produce a false colour effect. The solution I found was to make a custom WB profile for ACR using Adobe's free DNG Profile Editor.

Here's a link to the download.

http://www.adobe.com/support/downloads/ ... ileID=5490

This is the support documentation. I suspect that as with infrared, tutorial 4 will be the most relevant to you, but you might need to play around with the tool to get the best results.

http://wwwimages.adobe.com/www.adobe.co ... tation.pdf

You might also find this article on Luminous Landscape useful.

http://www.luminous-landscape.com/revie ... iles.shtml

(EDIT: I initially posted an incorrect link. The post now gives direct links to the application and support documentation. I also added the link to Luminous Landscape.}

[Mike Farley]

Note that I have made some corrections to my earlier post. I hope that you find this information useful.

[Mike Farley]

In order to use the DNG Profile Editor, it is necessary to have a DNG Raw file as an input. Since most cameras do not produce DNG files and have their own proprietary formats, Adobe has released a free converter which is updated regularly as new cameras are introduced. This, of course, is another reason to shoot in Raw when it is likely that some degree of post processing will be required to create the final image.

This is the Windows version:

http://www.adobe.com/support/downloads/ ... rm=Windows

And Mac:

http://www.adobe.com/support/downloads/ ... atform=mac