10 Replies Latest reply on Aug 10, 2018 4:19 PM by givemeafreakingbreak

    "Undo" auto-iso to equalize exposure

    givemeafreakingbreak Level 1

      Hello all,

      As part of a photogrammetry project, I took a number of photos of an object using manual settings on a D800.  However, I forgot to turn off auto-iso (argh!).  So, all my photos have the same aperature and shutter speed, but they differ in their ISO.  Is there some way I can calculate the exposure adjustment needed in each photo to remove the effect of the changes in ISO between photos,  such that they will have the same exposures across photos as I originally intended?

       

      I think the adjustment in EV units would go something like this: exposure_adjustment = -log2(ISO/baseISO).  Any thoughts about how to carry that out?

       

      Thanks,

      Allie

        • 1. Re: "Undo" auto-iso to equalize exposure
          F. McLion Adobe Community Professional & MVP

          You can not undo the effect it had while shooting.

          Doubling the ISO (i.e. from 100 to 200) adds a step to the EV (i.e. 12 to 13). So, it's easy to calculate

          • 2. Re: "Undo" auto-iso to equalize exposure
            givemeafreakingbreak Level 1

            I would count "equalizing exposure" as "undoing" the effect while shooting.  I know there are other ancillary effects (noise, etc), but as the thread title indicated, my main goal is to equalize exposure.

             

            I have a couple hundred photos.  The question is, is there any way to automate this calculation and apply the appropriate exposure compensation to all of them in lightroom?  For example, standardize everything to ISO 1000, and thus apply an exposure compensation of -log2(ISO/1000) to each photo?

             

            Thanks,

            Allie

            • 3. Re: "Undo" auto-iso to equalize exposure
              F. McLion Adobe Community Professional & MVP

              AFAIK, there is no automatic for this ... there's no need actually.

              I still do not understand what you expect to achieve.

              Even with Auto-ISO, the camera takes every shot perfectly set. This is like when you change the shutter speed and the aperture accordingly (i.e. Program-Shift) - it will result in the same picture taken, in terms of EV. ISO only adds a third variable and the camera would still use the very same EV.

              • 4. Re: "Undo" auto-iso to equalize exposure
                givemeafreakingbreak Level 1

                Appreciate your reply, though I must emphasize that I do have a need for this, even if you don't understand it.  Too bad there's not a way to achieve it in lightroom, alas.  Would be nice to have some sort of programmatic way to adjust exposure based on metadata.  Maybe I'll have to turn to ImageMagick or something like that.  Is there no plugin that might allow this?

                 

                I am using this for photogrammetry, and hence have hundreds of photos of an object from multiple angles.  I am trying to have every picture taken with the exact same settings.  At this point, the best I can do is to correct the photos after the fact.  If the scene from one angle is dark... then the photo should be dark.  If it is light from another angle, then it should be light.    I want dark sides to be dark, light sides to be light, etc.

                • 5. Re: "Undo" auto-iso to equalize exposure
                  F. McLion Adobe Community Professional & MVP

                  Got it. You need consistent exposure and the ISO-Auto acted like it is in P mode, adjusting EV.

                  • 7. Re: "Undo" auto-iso to equalize exposure
                    JimHess Adobe Community Professional & MVP

                    I have been caught by this error in shooting before myself. Unfortunately, there doesn't seem to be a way to override it. The camera exposed the image the way it was set to do so. It's one of those "lesson learned" errors that we all have to grow from.

                    1 person found this helpful
                    • 8. Re: "Undo" auto-iso to equalize exposure
                      givemeafreakingbreak Level 1

                      uhh, a change in iso essentially just changes the exposure.  undoing that change in post-processing by adjusting exposure (brightness) is the way to "undo" it.  i don't understand what the big mystery is here.

                      • 9. Re: "Undo" auto-iso to equalize exposure
                        JimHess Adobe Community Professional & MVP

                        Yes, you can adjust the exposure. However, you cannot change the ISO at which the image was taken. Even if the camera wasn't set to auto ISO it is possible to adjust exposure. I'm just saying that if you wanted ISO 100 but the camera was on auto and took the image at ISO 250, there isn't any way for you to change that ISO setting. You can adjust the exposure, of course. But the ISO setting obviously isn't going to change. I'm not sure what your question is, really. Initially it seemed you were inquiring about undoing auto ISO. The image has already been taken, and I don't see any way to change that aspect of an image. I'm not sure what you expect to be able to do.

                        • 10. Re: "Undo" auto-iso to equalize exposure
                          givemeafreakingbreak Level 1

                          Hi... yes, of course you can't actually change an exposure setting post-hoc, save for something like white balance in a RAW photo.  But aperture, shutter speed, iso... those are all baked in, i understand that.  The closest one can come to "undoing" an iso setting, given my needs, are to adjust exposure based on the -log2(iso/base iso) formula i believe.  anyway, thanks all for the attention, i think this has become more of a distraction than anything else for all involved...