Flat fielding how-to?

[Hening Bettermann]

Hi!

Can anyone point me to a simple step-by-step guide to flat fielding? Some googling takes me to sites for astro photographers, and I get the impression that I need special software, and maybe something like an ExpoDisc? Is that so?

The use would be to shoot a Passport ColorChecker with just 1 SoLux lamp and correct the unevenness of the lighting, as suggested by Iliah Borg. My lighting with 2 lamps is not even enough.

Thank you for your tips.

[AlterEgo]

I get the impression that I need special software, and maybe something like an ExpoDisc? Is that so?

software yes (some people can use generic matlab though or even excel)... 2nd shot of a flat even color/reflectance surface (in the same place under the same light, etc as your target shot is needed as a flat field).

The use would be to shoot a Passport ColorChecker with just 1 SoLux lamp and correct the unevenness of the lighting, as suggested by Iliah Borg. My lighting with 2 lamps is not even enough.

1) rawdigger = hit the website, instructions/example there = for example : http://www.rawdigger.com/usermanual/sampleswindow/save
2) dcamprof = hit Torger's webpage - manual/tutorial there (along with flare correction - where for example a target with greyscale patches spreaded in between color patches is a great thing) = http://www.ludd.ltu.se/~torger/dcamprof.html

[Hening Bettermann]

Thank you so much for your fast reply! I have something to study.
Good light!

[TimoK]

Flat field correction in RawTherapee, see RawPedia

[bjanes]

Hi!

Can anyone point me to a simple step-by-step guide to flat fielding? Some googling takes me to sites for astro photographers, and I get the impression that I need special software, and maybe something like an ExpoDisc? Is that so?

The use would be to shoot a Passport ColorChecker with just 1 SoLux lamp and correct the unevenness of the lighting, as suggested by Iliah Borg. My lighting with 2 lamps is not even enough.

Thank you for your tips.

Lightroom has a flat field plugin that might accomplish your objective.

Flat Field Plugin

Bill

[AlterEgo]

LCC type of things is not exactly what OP needs in this particular quest to flat field a target for camera profiling... that's why tools (rawdigger, dcamprof) used for camera profiling / in camera profiling workflow do implement what OP needs

[Tim Lookingbill]

Was I wrong about the definition of "Flat Fielding" of lenses. For those under the same misconception there is this pdf... http://labsdownload.adobe.com/pub/labs/lightroomplugins/lightroomplugins_dngff_docs.pdf off Bill's link.

I do think the OP is asking too much of this type of correction from software. Symmetrically flip-flopping with a copy paste routine of one sided illumination of a scene lit by one light source was a big PITA in the traditional darkroom, so I'ld suspect the same using software.

Ever try to seemlessly match one off color next to another so you can't see where one starts the other stops. I gave up.

Someone post a sample of how this will work under the same conditions the OP describes. I've got to see this before I download anymore software.

I was hoping this thread would be about lens profile distortions that make objects in the distant in the middle of the frame appear the same size as how I see it in my DSLR's viewfinder. There's got to be something better than the current lens barrel transforms available.

I guess a flat field lens would be more efficient but I don't know where to find one that isn't expensive and will fit on my DSLR.

[Hening Bettermann]

Thanks to all who commented! - I don't use Lightroom, and RawTherapee only for defringing, for which it has a great tool. My raw converters are Iridient, and, most recently, Raw Photo Processor, the latter for Iliah Borgs camera profiles. But I want profiles for Iridient as well, so I am now studying Anders Torger's instruction, which is exactly what I need! Tim, both Iliah Borg and Anders Torger recommend illumination with just one lamp + flat fielding, so I'll give it a try.
Thanks again!