Anyone get Flat-Field Correction to work? - LR Classic 8.3

New Here ,
May 18, 2019 May 18, 2019

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What am I doing wrong? Position Calibration file and RAW file next to one another in the Library Grid view. Select both files. Library ->  Flat-Field Correction -> default boxes checked. No DNG file produced. Progress bar runs in a few seconds. Nothing comes out. No error messages. No DNG file anywhere on the computer. Tried checking other boxes in the dialog - no change. Same on both Desktop and Laptop same behavior. Mac OS 10.13.6. Stumped.

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New Here ,
May 18, 2019 May 18, 2019

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New information.

On my computer:

Flat-Field Correction works on .RAF Fuji files and Nikon D810 .NEF files but NOT D850 .NEF files.

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LEGEND ,
May 18, 2019 May 18, 2019

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To ask a dumb question, And, no, I have not used this yet, so perhaps very dumb.

For the D850, you used a calibration image specific to that camera and the lens in question? Not using one shot in the D810.

Different metadata for camera.

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New Here ,
May 18, 2019 May 18, 2019

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Yes. I shot each calibration frame with the corresponding camera and lens looking at a white computer screen with the lens set to the same F#, and focus position (infinity in this case since trying to correct an astro photo shot wide open) as the photo to be corrected. I have not tested but am pretty sure if the camera, lens, pixel count, and orientation doesn't match the correction will not work. Thanks for the suggestion.

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Adobe Community Professional ,
May 18, 2019 May 18, 2019

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rqfugate  wrote

I have not tested but am pretty sure if the camera, lens, pixel count, and orientation doesn't match the correction will not work. Thanks for the suggestion.

I tested using two different lens (Sigma 50mm, Canon 17-40mm) on a 5D MKII body and Flat Field DNG was created. I believe the camera has to be the same model. but not the lens. You would want both to be the same, but that appears to be the way it works currently.

Suggestion: Try using the Calibration reference file with a non-astro subject such as a building, person, anything, but clear night sky. The Flat Field function may be detecting the Calibration reference shot AND night Astro shot as two calibration files and simply closing w/o creating the DNG file.

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New Here ,
May 19, 2019 May 19, 2019

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Thanks, everyone for the suggestions. Todd put me onto the following.

As an astrophotographer I make lots of FLATS to calibrate my astro shots. Usually use the evening or morning twilight sky as a flat source. When I am in a bind and use the computer screen I also use a diffuser or fine vellum paper. The lens or telescope is focused at infinity so I get no artifacts at all - the file is very, very smooth. The computer file I have been using is like that. I have also made some flats with an expo disk on another lens (it is only 77 mm and doesn't fit the 105mm aperture) and as long as I am not trying to correct a nighttime sky image or daytime cloudless sky it works. It works on landscape images just fine. So the process does seem not to work on nighttime astro raw images, which is the only application I really have for Flat-Field Correction. A disappointment.

However, I have discovered that if I convert the RAW astro to a TIF, it works on astro images. Now that is not an extra step I want to make since I usually stack 30 or more sky images. It seems Adobe needs to make this simpler. Don't know what they are doing behind the scenes but whatever it is it is not allowing the process to work on night sky shots.

I will contact Adobe and put this info into their hopper and hope that someday something will come out the other end.

Thanks, everyone for your suggestions.

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Adobe Community Professional ,
May 19, 2019 May 19, 2019

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rqfugate  wrote

I will contact Adobe and put this info into their hopper and hope that someday something will come out the other end.

please post this as a 'Problem' in the Photoshop Family forum at the below link. Paste the link to that report in a reply here so others can add their comments and 'Me To' vote. Thank you!

Post a Conversation | Photoshop Family Customer Community

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New Here ,
May 25, 2019 May 25, 2019

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I have tried using the Flat-field correction as well. Shot the calibration frames with a flatfield diffuser light just for the purpose. At first I did not get it to work as is reported at the beginning of this thread. wat I tried is to correct one flat shot with an identical shot taken right after the first, just to see how well the the Flatfielding would work. Well it never created any dng while I tried to do that. Appearantly it recognizes both files as calibration files and does not correct any files. Only if I put a “regular“ photo in the folder with the calibration file, it will work fine, but I am not able to see how well a job it did. Also I fear that it will not recognize night sky photos as regular photos and that is exactly where I would be interested to use this method. Would be nice if this would be corrected to where you can assign the calibration files and the file to be corrected manually.

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Adobe Community Professional ,
May 25, 2019 May 25, 2019

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Adobe Community Professional ,
May 18, 2019 May 18, 2019

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rqfugate  wrote

I shot each calibration frame with the corresponding camera and lens looking at a white computer screen with the lens set to the same F#, and focus position (infinity in this case since trying to correct an astro photo shot wide open) as the photo to be corrected.

A computer screen is most likely going to have some non-uniformity of luminance and color temperture. There's also the issue of moire and frame rate versus shutter speed that will worsen the accuracy of the calibration shot. There's a good article on the subject here: Adobe Flat Field

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Adobe Community Professional ,
May 18, 2019 May 18, 2019

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Could those concerns be mitigated using:

  • A display known to have excellent uniformity, such as the more expensive NEC and Eizo displays
  • Focusing so that the display is completely out of focus, to blur moire
  • Using a very long shutter speed to take care of the display refresh rate

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Adobe Community Professional ,
May 19, 2019 May 19, 2019

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Below is a Calibration file created using my very uniform NEC PA272w monitor with the central 2/3 area of the screen filling the camera's frame. I can see streaks caused by moire' interference and speckles due to small non-uniformities in the screen. Whether or not this will affect the Flat Field DNG is dependent on the sample size Adobe has selected for calculating the vignetting and color shift correction. You can check your Calibration files by moving the LR Tone Curve end points inward to the sides of the histogram data as shown below.

Adobe needs to provide much more detailed user Help information concerning HOW to create the Calibration image files to insure the most accurate results.

Flat-Field Correction

"For best results, shoot the calibration frame with a plastic diffuser card under the same optical configuration i.e. same lens, f-stop number, focal length, focal distance etc. to create the calibration frame."

What diffuser card, how uniform does it need to be, what type of lighting, how do you insure uniformity concerning all of these possible influences. Remember, we are trying to correct small lens anomalies. If the Calibration image file also has equal or larger anomalies then we are not going to achieve proper correction.

img_2822.CR2 Screenshot.jpg

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Adobe Community Professional ,
May 19, 2019 May 19, 2019

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I don't believe Adobe will formally identify or recommend a product/vendor, but have read elsewhere that an ExpoDisc can be used.

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Adobe Community Professional ,
May 19, 2019 May 19, 2019

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The ExpoDisc is designed for white balance and has a non-flat knobby diffuser that may cause uneven illumination across the image frame. I'm sure it works fine for white balancing, but is pricey and really not designed for creating "flat field" image files. A simple lens a cap with a flat diffuser used with a neutral target such as a white balance card, a piece of white copier paper, or even a white wall should work better and is much lower cost. Make sure there are no shadows on the target and get close enough so that the camera's frame is inside the neutral target.

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Adobe Community Professional ,
May 19, 2019 May 19, 2019

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https://forums.adobe.com/people/Todd+Shaner  wrote

The ExpoDisc is designed for white balance and has a non-flat knobby diffuser that may cause uneven illumination across the image frame. I'm sure it works fine for white balancing, but is pricey and really not designed for creating "flat field" image files.

Your description of the ExpoDisc and its intended use is fine. However, your other points are at odds with those who have some experience of using it with Flat Field. Put another way, had the info not come from the source that it did, then I would not have mentioned it.

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Adobe Community Professional ,
May 19, 2019 May 19, 2019

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https://forums.adobe.com/people/Ian+Lyons  wrote

However, your other points are at odds with those who have some experience of using it with Flat Field. Put another way, had the info not come from the source that it did, then I would not have mentioned it.

Ian, on ExpoDisc's website the make no mention of using their ExpoDisc product for creating Flat Field Calibration image files. I find it difficult to believe that's a "marketing" over site. For white balancing the only requirement is that the diffuser provide a truly neutral light filtering across the image frame. Light fall off or other "uneven" illumination is of no consequence for setting white balance, but it is an issue when creating Flat Filed Calibration files. Interestingly when creating Flat Field Calibration images color shift caused by the diffuser is of no consequence as long as it remains the same across the image frame.

It's easy enough to test by taking a picture of an evenly illuminated and even toned target such as a white balance card. Take a picture with the Expodisc and then again with it removed making sure all settings and lighting remain the same. Then inside LR use the WB Eyedropper to measure the Luminace L value and  A B Color values with the Histogram set to 'Show Lab Color Values. It will be necessary increase the LR Exposure setting in the ExpoDisc file (or decrease it in the other file) to correct for the overall light falloff of the ExpoDisc. The readings should remain the same when measured at the same places in both image files.

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LEGEND ,
May 18, 2019 May 18, 2019

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I see that some of the Adobe online directions were calling for or perhaps. recommending using a plastic diffuser card, an an example of that would be a Expo-Disk (and now I cannot provide a reference on that).

One source talks about using a flat white wall.

Adobe Flat Field

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LEGEND ,
May 25, 2019 May 25, 2019

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Looks like part of the issue is the clear as mud instructions at Adobe,at least the following one:

Flat-Field Correction

First or last image included in a selection of images to be corrected must be the calibration frame. Lightroom attempts to if determine first or last is it, chooses one, and treats either those following it as normal, Just how does LR determine that, and what if it gets it wrong. And does our sort order effect what lightroom thinks is first or last. And just how to create the calibration frame.

So, on to searching for better info?

Here is one, hmm, this is where I noticed an expo-disk mentioned;;

https://lightroomkillertips.com/may-2019-update-for-lightroom-classic-lightroom-and-adobe-camera-raw...

That page seems to treat this a a one image correction.

Oh and:

https://laurashoe.com/2019/05/14/whats-new-in-lightroom-classic-8-3-may-2019-release-new-features-an...

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LEGEND ,
May 25, 2019 May 25, 2019

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Having looked at:

https://laurashoe.com/2019/05/14/whats-new-in-lightroom-classic-8-3-may-2019-release-new-features-an...

Are you sure that the DNG file was not created and the original RAW file removed from the catalog, and you are looking at the new DNG?

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Adobe Community Professional ,
May 25, 2019 May 25, 2019

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davidg36166309  wrote

Having looked at:

https://laurashoe.com/2019/05/14/whats-new-in-lightroom-classic-8-3-may-2019-release-new-f eatures-a...

Are you sure that the DNG file was not created and the original RAW file removed from the catalog, and you are looking at the new DNG?

A request to retain the original raw file in the catalog along side the Flat Field DNG file has been made at the below Problem report. I also added the issue of astrophotography images being detected as calibration frames. Please add all further comments at the below link along with your 'Me To' vote and 'Follow.' Thank you.

New Flat-Field Correction DNG should not remove/replace the original RAW in the catalogue | Photosho...

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LEGEND ,
May 25, 2019 May 25, 2019

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Ahh a much much better discussion on how:

Adobe Flat Field

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Adobe Community Professional ,
May 26, 2019 May 26, 2019

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I already posted that link in my reply #8 above. As I suggested let's continue the discussion at the above mentioned Photoshop Family post. This is the best way to get Adobe's attention and have them address the current usability issues with the Flat Field correction tool in LR Classic.

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