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Author Topic: Raw file batch calibration/sync of image exposure?  (Read 8948 times)

CovaH

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Raw file batch calibration/sync of image exposure?
« on: July 09, 2015, 01:47:54 AM »
Thought I'd ask around here as people most likely have run into this problem while working with photoscan data.

I have 300+ images with exposure that varies slightly from image to image that I don't wan't to go through by hand. Does anyone know of a way to select a target image that I've calibrated correctly and have all other images match the exposure towards the calibrated one I selected?

I tried lightrooms "match total exposure" but couldn't seem to get it to work properly, maybe it's not what I want? I'm no real lightroom user so I don't know if I was just doing it wrong.

Seems like it would be rather easy for a program to batch align exposure/histogram vs a corrected image, atleast at a rough level?

Marcel

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Re: Raw file batch calibration/sync of image exposure?
« Reply #1 on: July 09, 2015, 08:03:28 PM »
Yes, it's a real shame that Photoshop's Auto Exposure cannot be used on multiple images.

As soon as you enable "Auto Exposure", it messes up the contrast big time. Reverting those settings on multiple images at the same time is not possible (neither is syncing), you would have to set them back to their defaults one image at a time.

What I think is happening, is that Adobe Camera RAW enters a different mode when Auto Exposure is enabled. If you save the settings and check the XMP file, you will see that the Exposure isn't stored in the file either.

I filed a bug report with Adobe, but the knowledge of the customer support was terrible. All you get is "could you please uninstall and reinstall the program, it will fix the problem!".




CovaH

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Re: Raw file batch calibration/sync of image exposure?
« Reply #2 on: July 09, 2015, 11:06:57 PM »
Haha, yeah that's a always a helpful answer. I had the same experience from the "auto" button, I don't know what it did, just moved around every slider randomly. I suspect there might be more steps to getting it working correctly, I'll have to look it up I suppose.

I have to say though, from my experience when working with computer programs of all types, it feels like I spend three times as much time troubleshooting things than actually working on what I'm supposed to nowadays. :P

bigben

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Re: Raw file batch calibration/sync of image exposure?
« Reply #3 on: July 09, 2015, 11:27:47 PM »
I use Bridge/ACR to manually adjust the exposure. 2 monitors, each with a Bridge window. Largest size thumbnail of reference image in one. Filter the other by shutter speed, open all of the images in ACR and adjust exposure and contrast settings to match the reference image.  For small differences adjusting the exposure is often all that's needed but as the exposure differences get larger (>1.5ev) you have to get a little more creative.  After adjusting the settings save as TIFF to to new folder.

Marcel

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Re: Raw file batch calibration/sync of image exposure?
« Reply #4 on: July 09, 2015, 11:32:31 PM »
Haha, yeah that's a always a helpful answer. I had the same experience from the "auto" button, I don't know what it did, just moved around every slider randomly. I suspect there might be more steps to getting it working correctly, I'll have to look it up I suppose.

It does actually equalize the exposure between photos fairly well, but the problem is that it also messes up the Contrast, Whites, Blacks settings  of the image.  Ideally you would just use 'Auto' to get the exposures equalized, and then set the rest of the settings back to 0. But you cannot edit (or sync) multiple image at the same time anymore with Auto exposure enabled.

To reproduce:

Open 20 RAW files in Camera RAW
Select all images
Click 'Auto' under the 'tint slider'
Observe that settings change on all images
 
Now with the images still selected, change any of the following settings (but *NOT* the Exposure slider!):
- Contrast
- Highlights
- Shadows
- Whites
- Blacks

You will see that only the settings on the first image (or sometimes first few images) are updated, the other images are not edited.

When you change the Exposure slider, the other settings are indeed updated (probably because the 'auto' mode is disabled).

We've looked into this any way possible, but there just doesn't seem to be any way around it.

Manually adjusting exposure like Bigben suggest is of course possible, but really mind-numbing work. :(

bigben

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Re: Raw file batch calibration/sync of image exposure?
« Reply #5 on: July 10, 2015, 12:15:30 AM »
Which is why I try and shoot with just 1 exposure  ;)
Expose as high as possible ignoring the sky blowing out

mala

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Re: Raw file batch calibration/sync of image exposure?
« Reply #6 on: July 10, 2015, 12:13:05 PM »
You could try using Raw Therapee  --  http://rawtherapee.com/

You should be able to save a " profile" for one image and then apply this to all the others and batch them

Hope that helps,
mala

Marcel

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Re: Raw file batch calibration/sync of image exposure?
« Reply #7 on: July 10, 2015, 09:54:59 PM »
Which is why I try and shoot with just 1 exposure  ;)
Expose as high as possible ignoring the sky blowing out

Yes, but sometimes the lighting condition changes (like thin with overcast clouds, or just before sunset) and the exposure of your photos will vary even with the camera in M mode.

@Mala: I'll look into RAWTherapee, sounds interesting!

chadfx

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Re: Raw file batch calibration/sync of image exposure?
« Reply #8 on: July 11, 2015, 01:30:11 AM »
+1 for bigben's approach (or do the same in Lightroom)...it's usually fairly quick work and most of the time is 'close enough'. I haven't found Photoscan to be particularly sensitive to minor variations anyway

If you really want to get fancy, you could put all of the images as a sequence into a compositing tool, like Nuke, sample/average the values and automatically apply the necessary corrections to the images...but it also might get thrown off if the subject matter in the images varies too greatly

I didn't see anything on the RAWTherapee web pages that would do any sort of automatic exposure balancing across a series of image.