10 Replies Latest reply on Nov 24, 2008 8:25 PM by (Jeff_Schewe)

    ACR Defaults and Dynamic Range

    Bill_Janes Level 2
      The tone curve in ACR has a profound effect on the dynamic range of the rendered image, and often this is not appreciated by users. To demonstrate the effects of the tone curve on DR, I photographed a Stouffer step wedge with the Nikon D3 and rendered the image into a TIFF with various tone curves and determined the resulting dynamic range with Imatest.

      Here is the target rendered with the ACR defaults for this camera, which include a black point of 5 (downsampled and shown as a JPEG):

      http://bjanes.smugmug.com/photos/422699368_FRdKT-O.jpg

      Shown below is the resulting characteristic curve as determined by Imatest along with the DR and other data. The total dynamic range is only 7.64 stops. This low DR results from the default black point of 5, which rolls off the darker tones as shown on the graph.

      http://bjanes.smugmug.com/photos/422697342_tnUFo-O.png

      By setting the black to 0, the total DR is increased to 12.3 stops and the useful photographic DR according to various quality levels is shown.

      http://bjanes.smugmug.com/photos/422697338_5e8pv-O.png

      One can also use a linear tone curve by setting all the basic settings to 0 and the point curve to linear.
      http://bjanes.smugmug.com/photos/422697332_u59B5-O.png

      For convenience, the tone curves are shown together here.

      http://bjanes.smugmug.com/photos/422697328_26BFV-O.gif

      One might wonder why Adobe chose a default black value of 5 for the D3, since it severely limits dynamic range by rolling off the blacks. The probable answer is that the full DR can not be reproduced on screen or in print without using a tone curve that would give the image a flat and unattractive appearance. Note that the darker steps of the Stouffer wedge are not distinguishable on the screen but differences can be noted if one measures the values with the eyedropper in PS. The default setting of 5 rolls of shadows which would not be reproduced and enhances contrast in the remaining image.
        • 1. Re: ACR Defaults and Dynamic Range
          michael shaffer Level 1
          Aren't you improving the DR relative to the low end of the histogram, as opposed to the high end? One might claim that DR is DR, but allowing for more noise at the low end is different than increasing the DR with respect to the high end, where everyone wants it(?)
          • 2. Re: ACR Defaults and Dynamic Range
            Dennis 1111 Level 2
            Interesting analysis but I tend to agree with Michael. The defaults of 5 Black and Medium tone curve I think are there for two reasons that are strongly related:
            1. come reasonably close to the camera manufacturer's software.
            2. hide noise in the shadows (and #2 connects strongly to #1 since it is the camera manufacturers that don't want you to see the noise lurking in those shadows).

            At least ACR gives us the option to open those shadows up if we want to (and gives us the option to set 0 Black and Linear tone curve as Defaults if we want). Canon DPP, for example, blocks up the shadows even more than ACR at its standard defaults and there is not much you can do about it there. I don't know about Nikon.
            • 3. Re: ACR Defaults and Dynamic Range
              Level 1
              >One might wonder why Adobe chose a default black value of 5
              >The default setting of 5 rolls of shadows which would not be reproduced and enhances contrast in the remaining image.

              Seems you discovered the answer yourself...and 12.3 stops in DR is self-massage...that ain't "usable" DR...it's "measurable" DR...I still wonder if Nikon couldn't get better DR if they lowered the base ISO to 100 instead of 200. Idle wondering since I don't use (or care about) Nikons...
              • 4. Re: ACR Defaults and Dynamic Range
                Bill_Janes Level 2
                Bill Janes wrote:
                >One might wonder why Adobe chose a default black value of 5 The default setting of 5 rolls of shadows which would not be reproduced and enhances contrast in the remaining image.

                Jeff Schewe wrote:
                >Seems you discovered the answer yourself...and 12.3 stops in DR is self-massage...that ain't "usable" DR...it's "measurable" DR...I still wonder if Nikon couldn't get better DR if they lowered the base ISO to 100 instead of 200. Idle wondering since I don't use (or care about) Nikons...

                As you and Bruce state in Real World ACR for PSC3, the default of 5 may be a bit aggressive and I agree. The default value of 5 gives a total DR of 7.64 which is well under what the D3 can deliver in practical photographic situations. The value of 12.3/stops is not "self massage", but rather the total DR determined by the noise floor used by Imatest. If you look at the Imatest DR results, you would see that the DR for low, medium, medium-high and high quality results is 11.6, 10.4, 9.1 and 8.05 f/stops respectively. DPreview gives a DR of 8.6 stops in their review of the D3.

                According to Roger Clark, the DR of the D3 is 13.7 f/stops using the engineering definition of DR. This is how Kodak reports the DR of their sensors.

                Since ACR supports Nikons and you write about ACR, I would think that you should have some interest in Nikon cameras
                • 5. Re: ACR Defaults and Dynamic Range
                  Level 1
                  >Since ACR supports Nikons and you write about ACR, I would think that you should have some interest in Nikon cameras

                  Why? Real World Camera Raw is platform agnosticaside from the fact that most all of the images contained in the book happen to come from cameras Bruce and I had/have and those are Canons. To the best of my knowledge, there is nothing in Camera Raw that is camera model dependent except for the DNG Profiles and the baseline demosiacing and noise reduction which vary camera by camera. Why should I care about the Nikon D3 specifically? It's only one of over 200 camera models Camera Raw supports.
                  • 6. Re: ACR Defaults and Dynamic Range
                    Ian Lyons MVP & Adobe Community Professional
                    Jeff,

                    There's also the Nikon mini SDK for White Balance, although I don't know if it applies to newer models.
                    • 7. Re: ACR Defaults and Dynamic Range
                      Bill_Janes Level 2
                      >Why? Real World Camera Raw is platform agnosticaside from the fact that most all of the images contained in the book happen to come from cameras Bruce and I had/have and those are Canons. To the best of my knowledge, there is nothing in Camera Raw that is camera model dependent except for the DNG Profiles and the baseline demosiacing and noise reduction which vary camera by camera. Why should I care about the Nikon D3 specifically?

                      In 35 mm style dSLRs (which I would venture to say are used by the vast majority of ACR users) Nikon and Canon are the two major brands. One thing that is camera specific is the baseline exposure offset that ACR uses for these cameras. For the Nikon D3 (and other recent Nikon cameras), ACR uses a baseline exposure offset of +0.5 EV. If you don't know this and try to expose to the right as much as possible, the histogram will appear overexposed in ACR when in reality the channels are far from clipping.

                      This is demonstrated in the following screen capture using ACR defaults with an Exposure value of 0. The highlights of the target appear blown.

                      http://bjanes.smugmug.com/photos/423897106_wvzqw-O.png

                      They also appear blown using the new beta profile, which does not take the baseline exposure offset into account.

                      http://bjanes.smugmug.com/photos/423897066_xeHoi-O.png

                      Looking at the raw histogram with Rawnalize, we see that the channels are not blown:

                      http://bjanes.smugmug.com/photos/423898181_md3kC-O.png

                      And here are the actual raw values for the red, green and blue channels (highlighted) of Step 1:

                      http://bjanes.smugmug.com/photos/423901972_MguxL-O.png

                      The raw headroom in each of the color channels (as shown in the raw histogram) also has something to do with the amount of highlight recovery that is possible. I would think that these considerations would be of inerest to the readers of your Camera Raw book.
                      • 8. Re: ACR Defaults and Dynamic Range
                        Level 1
                        > I would think that these considerations would be of inerest to the readers of your Camera Raw book.

                        Well, the book is about Camera Raw, not how to use your cameras...with over 200 cameras supported by Camera Raw and DNG, telling each camera user how Camera Raw deals with their individual camera's raw captures in the book is a bit over the top, don't ya think? I've got other things to do besides investigate cameras i don't use. I'll leave that to you..
                        • 9. Re: ACR Defaults and Dynamic Range
                          Bill_Janes Level 2
                          >with over 200 cameras supported by Camera Raw and DNG, telling each camera user how Camera Raw deals with their individual camera's raw captures in the book is a bit over the top, don't ya think?

                          Individually covering 200 cameras would be over the top, but discussion of the baseline exposure offset with an example would be helpful to many users. The purpose of the baseline offset is to ensure that images taken with different cameras at the same ISO would have a similar appearance, but it makes things difficult for those using the ACR histogram in judging the adequacy of ETTR.
                          • 10. Re: ACR Defaults and Dynamic Range
                            Level 1
                            >The purpose of the baseline offset is to ensure that images taken with different cameras at the same ISO would have a similar appearance, but it makes things difficult for those using the ACR histogram in judging the adequacy of ETTR.

                            Sausage making, I think...I like to eat them, don't like to write about how ya make them.