FlatField-Correction still bad AF -IF it works

Forum|Forum|5 years ago
August 25, 2020
4 답변들
2897 조회

So, since i try to use the embedded FFC in LR, it does not do the job properly!

Adobe-Support could not- or want not help me, so i'm looking for more experienced users.

1. not every image will process, no message is given about this

2. Some of the ones which will, cause damage like some ghosting (like in the attachment)

3. The other, seemly correct processed images will have a strong gamma-shading, useless to reproduce images in a professional way. (example in attachment)
-Highlights getting dropped down, shaddows pushing up, midtones are "ok". For example, the white field on my Target is about L = 93 if it is set at the center.. at the corner of my image, the same field is pushed down to L = 86. Midtones from around 50 to 51 and shaddows from 18 (for example) to 21.
This is clearly not what i want and even not what it is supposed to be.
Struggling around with this, i noticed that the lens-profiles does the same thing when try to eleminate vignetting, but not as hard as the FFC.

Anybody here with the same problems??

I also asked Adobe if it could be better to use a gray-"card" instead of nearly white to set the reference-image, but received no answer. I'm realy unsatisfied about the support they gave me overall.

best regards
Niklas

이 주제는 답변이 닫혔습니다.

J

jank0324

Participant

I have a very particular use case where my flat field image always has a black frame around the uniformly lit area. The same frame is in all the images I would like to correct, as well. Unfortunately, when I try using the flat-field image for flat-field correction, Lightroom detects that it isn't uniformly lit and doesn't let me use it.

I have found a little workarond, by exporting all images with the frame cropped out, then reimporting them and applying the flat-field correction to the new files. This does however take quite some time (I have to do thousands of photos on a regular basis) and defeat the purpose of a RAW workflow.

Is anyone aware of a better way, for example to trick the flat-field correction into using the flat-field image anyway?

cmgap

Community Expert

Can you post screenshot examples of your staging? Why shoot with the frame in the image - it doesn't seem like that is saving you time if you have to crop it out to make corrections? If the set is always the same why not just add the frame after?

J

jank0324

Participant

Here is an example of one of my flat-field images. Note the black frame on the outside. Unfortunately I cannot capture without this frame as a result of the optical setup I'm using (basically a macro lens taking photos of a Super 8 fiom gate).

J

jank0324

Participant

So this may be a slightly odd one, but I have a use case where a regularily need to apply flat-field correction to a couple thousand photos on one go, meaning I have one flat-field image and a couple thousand images to correct.

Now I've noticed, that, as soon as I select more than the flat-field image and 99 images to correct, the menu item for flat-field correction is deactivated. This effectively means that I have to do the correction in chunks of 99 photos at a time, which in my case can take forever.

Is there any way to work around this and apply the flat-field correction to more photos in one go?

aarons44285769

Participating Frequently

haev you found a solution?

N

nikc8180200

Participating Frequently

So far as i can say today, the best solution seems to use another software unfortunately.
Or can someone say something different today?
Best regards
Niklas

J

Jao vdL

Community Expert

I have never done this but if I read the instructions here: https://helpx.adobe.com/lightroom-classic/help/flat-field-correction.html it seems to imply you should use a plastic diffuser card like an expo disc for the reference image. It sounds like you're using gray or white cards. Apparantly a diffusor in front of the lens is what is supposed to work well: https://www.lightroomqueen.com/community/threads/flat-field-correction.37750/

N

nikc8180200

Participating Frequently

Yes, you're right.. in the case you want to eliminate vignette and colorcast of your Lens+Cam-Combination that's the way to go..
But in my case it is used to correct small uneven illumination too. Which is the usal way to reproduce images in Studio because you simply can't illuminate the surface perfect homogeneus.

J

Jao vdL

Community Expert

Ah! Not knowing anything about how the flat field correction is implemented, my guess would be that the correction is based on a typical spherical model of lens and sensor with at best a quadratic radial curvature of the vignetting and color shift. It probably doesn't work for uneven illumination that doesn't fit this sort of spherical/radial behaviour. I would probably look at Photoshop using the reference images as overlay to color/intensity correct in a layer or using the math functions. That will take much more effort to get right