19 Replies Latest reply on Jul 21, 2011 5:17 AM by Bill_Janes

    Does the ACR histogram reflect the full image?

    celboy Level 1

      I am trying to streamline camera raw file preperation into a 3rd party color corrector.

       

      When I take a raw and zero out all the settings, how come things can still be clipped out?

       

      Isn't everything that is captured ---therefore in the histogram?

       

      How do I linearize the files? And shouldn't they come out dark? Thats my experience with linear files from high speed video cameras.

       

      Ideally I would like 16bit tiffs reflecting the sensor capture.

       

      But I don't have all day to manually customize every setup on ..say 100 cr2's?

       

      Any tips would be most appreciated.

       

      thanks,

      Tom

        • 1. Re: Does the ACR histogram reflect the full image?
          Jeff Schewe Level 5

          celboy wrote:

           

          But I don't have all day to manually customize every setup on ..say 100 cr2's?

           

          Any tips would be most appreciated.

           

           

          Well...every shot deserves an optimal image setting (images that fall into the exact same exposure setting will generally need the same settings). Tips? Learn how to be efficient when working in ACR/LR...ain't all that hard.

          1 person found this helpful
          • 2. Re: Does the ACR histogram reflect the full image?
            deejjjaaaa Level 2

            then may be you do not need a raw converter like ACR, but rather a command line utilities like examples supplied w/ libraw ( http://www.libraw.org , which is a more "human" version of dcraw code ) -> compiled binaries @ http://www.libraw.org/download#alpha

            1 person found this helpful
            • 3. Re: Does the ACR histogram reflect the full image?
              Level 4

              celboy wrote:

               

              …When I take a raw and zero out all the settings, how come things can still be clipped out?…

               

              That's a very easy one to answer:  the image is overexposed.

              • 4. Re: Does the ACR histogram reflect the full image?
                ssprengel Adobe Community Professional & MVP

                The histogram is the data in terms of the output colorspace shown in the blue-link at the bottom.  The wider the colorspace, the more data is saved.  I use 16-bit ProPhotoRGB.

                • 5. Re: Does the ACR histogram reflect the full image?
                  celboy Level 1

                  No---it seems the histogram reflects the viewer. There is stuff in there providing I keep adjusting the exposure.

                  It just seems I have to to do this on every group of shots or setups. Bridge helps out with that.

                   

                  I've tried dcraw and I still get missing (clipped out) highlights.

                   

                  I just wanted the raw sensor capture ---as a 16bit tiff---preferrably linear--I can always add gamma later.

                  • 6. Re: Does the ACR histogram reflect the full image?
                    Yammer Level 4

                    Why don't you use the camera profile function built into ACR to correct colour? Are you aware that you can create a custom camera profile using your camera and a ColorChecker card, and Adobe's free DNG Profile Editor software? It makes a big difference, and it's a set-and-forget thing.

                     

                    Like others have said, the histogram represents the converted data, not the raw data. You can minimise saturation by setting ProPhotoRGB in the workspace options, and you can also set a small negative offset for Exposure in your defaults—some cameras actually require this anyway.

                    • 7. Re: Does the ACR histogram reflect the full image?
                      Bill_Janes Level 2

                      celboy wrote:

                       

                      When I take a raw and zero out all the settings, how come things can still be clipped out?

                       

                      Isn't everything that is captured ---therefore in the histogram?

                       

                      How do I linearize the files? And shouldn't they come out dark? Thats my experience with linear files from high speed video cameras.

                       

                      Ideally I would like 16bit tiffs reflecting the sensor capture.

                       

                      Tom

                      DCRaw or its libraw implementations can go the job, but if you prefer to work in ACR, the first step, as you have noted below, is to zero out the sliders on the main tab of ACR and set the tone curve to linear. Then you have to apply the BaselineOffset that ACR applies to the camera file. This value can be found by converting the raw to DNG, and reading the value with an EXIF reader. For the Nikon D3, the BaselineOffset is +0.5 EV and the image will appear overexposed and possibly clipped if you do not make this correction. To compensate for the +0.5 EV, you have to set exposure to -0.5 EV.

                       

                      Then render to 16 bit ProPhotoRGB in ACR. The image will have a gamma of 1.8. You can convert to linear (scene referred) by converting to the linear_RIMM-RGB_v4.icc profile as explained in this article on the ICC web site:

                       

                      http://www.color.org/scene-referred.xalter

                       

                      The gamma will be 1.0 and the image will appear dark if viewed in a noncolor managed program, but with Photoshop it will have a normal appearance. I don't know what color correction program you are using, but it might be easier to learn how to use ACR and the DNG profiler as Jeff Schewe suggested.

                      • 8. Re: Does the ACR histogram reflect the full image?
                        celboy Level 1

                        Re:Camera profiles

                         

                        I looked into this a little--but wouldn't this require I have the camera (which I don't--the client or production crew rented it) and have shot macbeths tests with it?

                         

                        Am I mistaken?

                         

                        thanks,

                         

                        Tom

                        • 9. Re: Does the ACR histogram reflect the full image?
                          celboy Level 1

                          Re: dcraw

                           

                          I tried these commands together--

                          -6        Write 16-bit instead of 8-bit

                          -4        Linear 16-bit, same as "-6 -W -g 1 1"

                          -T        Write TIFF instead of PPM

                          but the tiff was still clipped.
                          Am I missing one other command?
                          thanks everyone for the great feedback so far.
                          Tom

                          • 10. Re: Does the ACR histogram reflect the full image?
                            Yammer Level 4

                            celboy wrote:

                             

                            Re:Camera profiles

                             

                            I looked into this a little--but wouldn't this require I have the camera (which I don't--the client or production crew rented it) and have shot macbeths tests with it?

                             

                            Am I mistaken?

                             

                            No, that's correct. If you don't have the camera, you have to use one of the supplied camera profiles (Adobe or Camera Standard, for example) which are still pretty good—and it's worth checking the 'best' one of these is set as default, as well as zeroing your sliders.

                            • 11. Re: Does the ACR histogram reflect the full image?
                              Bill_Janes Level 2

                              Yammer P wrote:

                               

                              celboy wrote:

                               

                              Re:Camera profiles

                               

                              I looked into this a little--but wouldn't this require I have the camera (which I don't--the client or production crew rented it) and have shot macbeths tests with it?

                               

                              Am I mistaken?

                               

                              No, that's correct. If you don't have the camera, you have to use one of the supplied camera profiles (Adobe or Camera Standard, for example) which are still pretty good—and it's worth checking the 'best' one of these is set as default, as well as zeroing your sliders.

                               

                              Yammer P wrote:

                               

                              celboy wrote:

                               

                              Re:Camera profiles

                               

                              I looked into this a little--but wouldn't this require I have the camera (which I don't--the client or production crew rented it) and have shot macbeths tests with it?

                               

                              Am I mistaken?

                               

                              No, that's correct. If you don't have the camera, you have to use one of the supplied camera profiles (Adobe or Camera Standard, for example) which are still pretty good—and it's worth checking the 'best' one of these is set as default, as well as zeroing your sliders.

                              I agree with Yammer P. Whatever raw conversion program you use, you need some type of "profile" to convert from the camera space to the working space. The last time I looked at the source code for DCRaw, they used a matrix from Adobe. Another solution would be to take a ColorChecker shot with each set of photographs taken under the same conditions and use the X-rite profiler. Michael Reichman (Luminous Landscape) reviewed that solution recently and was pleased with the results.

                              • 12. Re: Does the ACR histogram reflect the full image?
                                ssprengel Adobe Community Professional & MVP

                                Is there a way to get the non-demosaicked data as a TIF, the one-color-per-pixel numbers?  Then you could see the original RAW numbers and understand if any of the photosites were maxed out.

                                • 13. Re: Does the ACR histogram reflect the full image?
                                  Jeff Schewe Level 5

                                  ssprengel wrote:

                                   

                                  Is there a way to get the non-demosaicked data as a TIF, the one-color-per-pixel numbers?  Then you could see the original RAW numbers and understand if any of the photosites were maxed out.

                                   

                                   

                                  You can run a command line using the DNG SDK and get out a non-demosiaced rendering of a raw file. The instructions are sorta in the DNG SDK (although I had to have the help of en engineer to do it, but that's just me :~).

                                  • 14. Re: Does the ACR histogram reflect the full image?
                                    Bill_Janes Level 2

                                    ssprengel wrote:

                                     

                                    Is there a way to get the non-demosaicked data as a TIF, the one-color-per-pixel numbers?  Then you could see the original RAW numbers and understand if any of the photosites were maxed out.

                                    If your camera is supported, the easiest way to view raw files is Photobola Rawnalyze. It has many options, but the easiest is the histogram as shown below. This is from the Nikon D3 with full ETTR of a Stouffer wedge. Note that no white balance is applied and the green channel is just short of clipping.

                                     

                                    http://bjanes.smugmug.com/Photography/Exposure/D3Histograms/i-fWHTh33/0/L/005rawhistogram-L.png

                                     

                                    Another way to analyze the image is with a program such Iris (astronomical freeware) that can look directly at raw files. Here is the green1 channel of the same file with the histogram shown by another freeware program (ImageJ from the National Institutes of Health). In a raw file, clipping can occur when the sensor saturates or the ADC overflows. Because of shot noise and pixel response nonuniformity, the histogram is bell shaped and some clipping can begin when the right edge of the bell curve begins to clip and clipping will be complete when the left edge of the bell curve reaches clipping.

                                     

                                    http://bjanes.smugmug.com/Photography/Exposure/D3Histograms/i-5rDpBNz/0/O/005g1histogram.png

                                     

                                    In practice, ACR with a linear tone curve and the proper exposure offset is accurate enough for most purposes. However, its output is white balanced and the red and blue channels can appear clipped from the white balance multipliers when the raw data in those channels are actually intact. Here there is slight clipping with the exposure offset of -0.5 EV, but it can be totally eliminated by using an exposure of -0.55 EV.

                                     

                                    http://bjanes.smugmug.com/Photography/Exposure/D3Histograms/i-M8WjhHm/0/O/05ACRclip.png

                                    • 15. Re: Does the ACR histogram reflect the full image?
                                      celboy Level 1

                                      Bill,

                                       

                                      So in your ACR pix, your WB & tint are not default. Is that Ok?

                                      Is "exposure" and below just need to be zero?

                                      As long as your histogram is balanced to match your grey step pattern?

                                       

                                      Thanks for the explanation.

                                       

                                      Tom

                                      • 16. Re: Does the ACR histogram reflect the full image?
                                        Level 4

                                        Sorry, celboy, I admit I'm not following you, nor am I familiar with your apparently idiolectal terminology.  More on that below.

                                         

                                        You are being assisted now by contributors with far more knowledge and patience, so I'm hopeful you'll get the clarifications you need.

                                         

                                        Just to clarify where I was coming from in my post:

                                         

                                        celboy wrote:

                                         

                                        No---it seems the histogram reflects the viewer…

                                         

                                        I have no idea what you mean by that.

                                         

                                         

                                        celboy wrote:

                                         

                                        …When I take a raw and zero out all the settings, how come things can still be clipped out?…

                                         

                                         

                                        My post—to which you were replying—simply stressed the point that "zeroing out all the settings" is in no way, shape or form going to eliminate clipping in raw captures you may have overexposed.

                                         

                                        I'm stepping aside now and I'll follow this thread from the sidelines.

                                         

                                         

                                         

                                        ____________

                                        Wo Tai Lao Le

                                        我太老了

                                         

                                         

                                         

                                        EDITED: overexposed

                                         

                                        Message was edited by: Tai Lao

                                        • 17. Re: Does the ACR histogram reflect the full image?
                                          Level 4

                                          Email users:

                                           

                                          please note I edited my last post to read overexposed.

                                          • 18. Re: Does the ACR histogram reflect the full image?
                                            Vit Novak Level 3

                                            ssprengel wrote:

                                             

                                            Is there a way to get the non-demosaicked data as a TIF, the one-color-per-pixel numbers?  Then you could see the original RAW numbers and understand if any of the photosites were maxed out.

                                             

                                            dcraw -D -T  <filename>      ... returns non-linear 8 bit non-demosaicked image

                                            dcraw -D -T -4 <filename>      ... returns linear 16 bit non-demosaicked image

                                            • 19. Re: Does the ACR histogram reflect the full image?
                                              Bill_Janes Level 2

                                              celboy wrote:

                                               

                                              Bill,

                                               

                                              So in your ACR pix, your WB & tint are not default. Is that Ok?

                                              Is "exposure" and below just need to be zero?

                                              As long as your histogram is balanced to match your grey step pattern?

                                               

                                              Thanks for the explanation.

                                               

                                              Tom

                                              I used a custom white balance since the shots were taken under 5000K florescent illumination on a light box. Exposure has to be -0.5 EV to account for the +0.5 EV baseline offset that ACR uses for this camera.