7 Replies Latest reply on Sep 29, 2015 4:16 AM by b2martin_a

    Kelvin Inaccurate

    Petrula Level 1
      Camera Raw 9.1.1

      Win 7 Pro 64-bit SP1

       

      Nikon D90

       

      I shot two raw files with the Kelvin white balance on the D90 at

      2,500K

      10,000K

       

      In ACR 9.1.1, White Balance: "AsShot" said

      Temperature: 2,600K Tint: +3

      Temperature: 8,800K  Tint: +14

       

      Why does the D90 Kelvin temperatures differ from the ACR "As Shot" Kelvin temperatures?

       

      The White Balance offset in the D90 was set to (0,0).

      Why does ACR show a Tint when the D90 White Balance Kelvin offset was zero?

       

      The same results occur for the DNG 9.1.1.461 files.

       

      Thanks in advance.

        • 1. Re: Kelvin Inaccurate
          Richard Southworth Level 3

          ACR ignores camera exif data, uses its own algorithms to calculate temperature and tint.  And I realize that does not explain why it's different.

           

          Richard Southworth

          • 2. Re: Kelvin Inaccurate
            Petrula Level 1

            If that is the case, it makes no sense.

            I hope one of the Adobe Staff could clarify this issue since it is important.

            It is further complicated by what effect Camera Calibrations tab | Camera Profiles have on the Kelvin and Tint.

            Thanks

            • 3. Re: Kelvin Inaccurate
              Richard Southworth Level 3

              I'm sure there are others who can articulate this better than I, but here goes:

               

              1. The WB settings on your D90 have nothing to do with the actual camera exposure, they are just tags in the metadata to "guide" software as to your intended rendering of the image within a chosen color space.

              2. I believe ACR is trying to determine the characteristics of the actual light present when the image was exposed, editing the image so neutral areas will measure out as R=G=B in the output color space.  The algorithm is more or less successful depending upon the characteristics of the image.  Thankfully they provide tools so that one can apply intelligence to the process.

              3.  White balancing requires modifications to all three channels, the kelvin number is not sufficient by itself.  The offset setting in the D90 is provided so that you can adjust the camera's auto white balance to your liking, doesn't bear upon the tint value chosen by ACR.

               

              Richard Southworth

              • 4. Re: Kelvin Inaccurate
                Richard Southworth Level 3

                And I must be incorrect in my previous post, ACR must to some degree be using the tags for guidance in the As Shot wb setting.  Obviously they don't apply them blindly, they have determined a "bias" for their calculation.  Most of the camera companies don't provide much info to Adobe to help them engineer their profiles, so the ACR engineers do what they consider to be the most accurate/useful result.

                 

                Richard Southworth

                • 5. Re: Kelvin Inaccurate
                  Richard Southworth Level 3

                  And I need to crawl out of another hole I created, i.e. "white balance requires modifications to all three channels".  Actually we can leave one channel alone, and only modify the gain coefficients on the other two channels.  Therefore we must have two variables to account for two channels - for historic reasons we choose the kelvin temperature, roughly equating it to moving along the yellow - blue axis, and "tint" for moving along the magenta - green axis.  It would be a lot less confusing IMO if it were represented by what actually occurs, i.e. changing the gain on two color channels relative to the third.

                   

                  Richard Southworth

                  • 6. Re: Kelvin Inaccurate
                    sandy_mc Level 3

                    Nikon cameras (mostly) encode white balance as (in Adobe speak) an "As Shot Neutral" value - in effect, the sensor reading that corresponds to a neutral color. So white balance is sensor referred.

                     

                    As a result, any change to camera profile (which is what controls the translation from sensor space to color space) will change the white balance as expressed in color space. As displayed WB will almost never exactly match the camera settings because Adobe and Nikon use different camera profiles.

                    • 7. Re: Kelvin Inaccurate
                      b2martin_a Level 2

                      I think other RAW converters will also give you a different value for the AS Shot white balance - not the Nikon value.  I think the RAW converter and the Camera Profile for that RAW converter both affect the values for white balance.  If you generate DNG Camera Profiles for Adobe RAW converters (Lightroom  and Camerea RAW) using X-Rite Passport software you will get different AS Shot white balance numbers than if using the Adobe Camera profiles.