16 Replies Latest reply on May 26, 2010 8:42 AM by Noel Carboni

    Desaturation of Near Overexposure Question

    Noel Carboni Level 7

      I hear Camera Raw 6.1 is around the corner.  Cool!

       

      I wonder whether any fundamental change has been made to change the way it responds to partial overexposure...  With my Canons at least, all the current versions of Camera Raw desaturate colors as soon as one of the color channels saturates.  Since we know that Canon's AA filter is bluish-green, this makes it highly likely the green and blue channels will saturate (max out) first before red.  As it should be, Camera Raw tries to recover at least some of the data using the red channel.

       

      So, for example, if the green channel saturates, the subject will turn kind of gray instead of leaving the blue and red channels alone.  Here's a graphic example:

      OverexposureComparison.jpg

       

      A long time ago I recall corresponding with Thomas Knoll on this and I believe the thinking was that if the color can no longer be accurately determined because of one or two channel overexposure then the color will be desaturated so that it will not shift, and in a sense be made inaccurate.  I recall thinking that gray is a color too, but Camera Raw is what it is.

       

      This philosophy may work fairly well for clouds in the sky, but it's not so good for some other things.  I think it also occasionally negatively impacts the way HDR images are assembled, as bright things end up with gray halos that don't mix well at all.

       

      Any chance there's an option in ACR 6.1 to disable this desaturation behavior?  If not, could we please have one in the future?

       

      As far as I can see Camera Raw is hands-down the best way to open raw exposures.  Making it work even better at the limits of exposure would be real icing on that cake.

       

      Thanks.

       

      -Noel

        • 1. Re: Desaturation of Near Overexposure Question
          JW Stephenson Level 4

          Noel,

           

          Have you tried the untwisted version of the DNG profile for some of these complicated images?  I think the discussion is still at http://thomaslesterphotography.com/photography/untwisted-adobe-camera-profiles/ .  It seems to work best for me when I am trying to keep skin tones consistent but it sounds like the same problem.

           

          Jeff

          • 2. Re: Desaturation of Near Overexposure Question
            Noel Carboni Level 7

            Thanks, I tried them and they don't help with this issue.  In fact, the untwisted profiles cause far worse black point clipping (see my other recent post) in addition to the grayed-out areas.

             

            As it turns out I have developed my own 40D profile to far more closely match the JPEG colors out of the camera than any of the provided profiles, and I crafted it so that it helps some with bringing all the dynamic range available into the images (for one thing, I set it up so I have to set the default exposure slider at -0.25 EV, which helps bring in otherwise lost highlights).

             

            The problem here really is just that Camera Raw falls into this "complete desaturation" mode when some number of the color channels are maxed out (presumably by copying the unsaturated channel data into the saturated channels).

             

            -Noel

            • 3. Re: Desaturation of Near Overexposure Question
              dorin_nicolaescu Level 5

              To clarify: what was the exposure of the left image in comparison to the right one?

              What software did you use to develop the left image?

               

              I wonder whether any fundamental change has been made to change the way it responds to partial overexposure... 

              Are you sure earlier versions of ACR treated same overexposed highlights differently (better?)

              • 4. Re: Desaturation of Near Overexposure Question
                Noel Carboni Level 7

                Camera Raw in all cases.  The left image was properly exposed.  The right image was overexposed (along the lines of exposure bracketing in anticipation of HDR work, though that's not what I was really doing).

                 

                Left image:    1/60 @ f/10 ISO 100

                Right image:  1/60 @ f/5 ISO 100

                 

                You misread my comment.  I was wondering whether perhaps ACR 6.1 (which I have not seen yet) has made a change in this area.

                 

                This problem has been around since around the advent of the widened negative range on the exposure slider - a long time ago.

                 

                -Noel

                • 5. Re: Desaturation of Near Overexposure Question
                  dorin_nicolaescu Level 5
                  The left image was properly exposed.  The right image was intentionally overexposed

                  Ok, that explains a lot.

                   

                  How much "RAW headroom" you think your camera has? +2EV sounds like a lot. I mean, you don't expect miracles from a raw converter, do you?

                   

                  What other raw converters do a better job than ACR on recovering highlights. I'm curious to try...

                  • 6. Re: Desaturation of Near Overexposure Question
                    Noel Carboni Level 7

                    In answer to your question "how much headroom...":  I (and/or the camera) metered this photo on a large dark area in it.  I think I noticed that while chimping and that's why I took another that's correctly exposed.  I'm well aware of the pitfalls of overexposure.  However, one may not always notice that highlights in an image are overexposed, and thus it would be REALLY NICE if ACR would handle the traversal across the edge of overexposure better.

                     

                    It's been a long while since I tried converting with another converter, and I haven't tried with this particular image, but back when I was doing comparisons I can say that the Canon converters all seemed to recover color better than Camera Raw in areas of near overexposure.  I don't even have Canon's converters on this computer (but now that you mention it, I should download their latest).

                     

                    Here are the raw files for the two images depicted above if you'd like to experiment:

                     

                    http://images.ProDigitalSoftware.com/IMG_3608.CR2  (the one that's overexposed)

                     

                    http://images.ProDigitalSoftware.com/IMG_3607.CR2

                     

                    -Noel

                    • 7. Re: Desaturation of Near Overexposure Question
                      Jeff Schewe Level 5

                      Noel Carboni wrote:

                       

                      http://images.ProDigitalSoftware.com/IMG_3607.CR2

                       

                       

                      I get a warning that the file doesn't exsist...got the other one.

                      • 8. Re: Desaturation of Near Overexposure Question
                        Jeff Schewe Level 5

                        Noel Carboni wrote:

                         

                        Any chance there's an option in ACR 6.1 to disable this desaturation behavior?  If not, could we please have one in the future?

                         

                        No...this is the way Camera Raw has worked since the recovery was split from the minus exposure controls back in Camera Raw 4 (I think).

                         

                        When you clip one or more channels, you loose the ability to generate accurate color so Camera Raw tries to give you textural detail even if the color won't be accurate. It actually works well when only one channel is clipped...it works less good when you have two channels clipped. Many converters actually quite trying to get image data past the first blown channel. You can do into the Adjustment Brush and paint in some color over the recovered texture...that's about the best you can expect. Once channels are blown, Camera Raw would have no idea what colors those blown channels WOULD have produced if they weren't blown so it'll be up to you to add the correct color.

                        • 9. Re: Desaturation of Near Overexposure Question
                          Hudechrome-sd9sPI Level 2

                          Sometimes that clipping/recovery actually improves color in highlights, specifically clouds, snow and ice. Removing a slight bluish cast to clouds with the usual methods can result in a balance of color that only approximates what the eye saw. A clipped highlight in the clouds using the slider to recover generates values closer to neutral in them, and so I'll shoot a frame for cloud values that require correction as well as a frame that doesn't. Then make my choice.

                           

                          I've seen and labored over the very problem the OP has with rock faces that have a semi-glare quality. I have been known to grab my Sierra cup, fill it with water and "wash" the face. Sometimes that backfires, so shoot firat then compensate.

                          • 10. Re: Desaturation of Near Overexposure Question
                            Noel Carboni Level 7
                            function(){return A.apply(null,[this].concat($A(arguments)))}

                            Jeff Schewe wrote:


                            No...this is the way Camera Raw has worked since the recovery was split from the minus exposure controls back in Camera Raw 4 (I think).

                             


                            That's it, just "No, we won't consider doing this"?

                             

                            The colors are in some cases better and in some cases skewed so that it will be much worse visually.  All I'm asking is an option to choose NOT to desaturate whatever color is remaining, however much it is skewed.

                             

                            -Noel

                            • 11. Re: Desaturation of Near Overexposure Question
                              Jeff Schewe Level 5

                              Noel Carboni wrote:

                               

                              That's it, just "No, we won't consider doing this"?

                               

                               

                              I'm saying it's working as designed and trying to get ANY data out of totally blown saturated photo-sites is SciFi...keeping the texture neutral is almost always the best solution...so you are asking for a feature which at best, would be of minimal usefulness the majority of the time.

                               

                              Just because it's digital and there's an ability to do a lot of post capture computational corrections doesn't alter the fact that over-exposing an image will have severe negative impacts on image quality...

                              • 12. Re: Desaturation of Near Overexposure Question
                                Bill_Janes Level 2

                                Noel Carboni wrote:

                                 

                                function(){return A.apply(null,[this].concat($A(arguments)))}

                                Jeff Schewe wrote:


                                No...this is the way Camera Raw has worked since the recovery was split from the minus exposure controls back in Camera Raw 4 (I think).

                                 


                                That's it, just "No, we won't consider doing this"?

                                 

                                The colors are in some cases better and in some cases skewed so that it will be much worse visually.  All I'm asking is an option to choose NOT to desaturate whatever color is remaining, however much it is skewed.

                                 

                                -Noel

                                 

                                 

                                Guillermo Luijk has a good discussion on white balance and highlight recovery in his tutorial on DCRaw, which does offer options for highlight recovery. See Figure 9 and the accompaning text in the tutorial. The option -H 9 attempts to reconstruct the highlights from adjacent non blown areas and worked will in his example with the girl's face.

                                 

                                http://www.guillermoluijk.com/tutorial/dcraw/index_en.htm

                                 

                                However, -H 9 did not work that well with your image:

                                 

                                HighlilghtReconstr.gif

                                • 13. Re: Desaturation of Near Overexposure Question
                                  Noel Carboni Level 7
                                  function(){return A.apply(null,[this].concat($A(arguments)))}

                                  Jeff Schewe wrote:

                                   

                                  Noel Carboni wrote:

                                   

                                  http://images.ProDigitalSoftware.com/IMG_3607.CR2

                                   

                                   

                                  I get a warning that the file doesn't exsist...got the other one.

                                   

                                  Oops!  Sorry, make that http://images.ProDigitalSoftware.com/IMG_3609.CR2

                                   

                                  I can't edit the post above any longer.

                                   

                                  function(){return A.apply(null,[this].concat($A(arguments)))}

                                    Jeff Schewe wrote:


                                  I'm saying it's working as designed

                                   

                                  And I'm saying the design could use more work.  You can call it sci fi but I've seen other converters do better with this (admittedly a while ago - I'm going to try to repeat that performance).  All I'm asking is for you (are you the one programming this software?) to consider adding an alternative method. It's not good enough as is.

                                   

                                  How things work at their limits is important.  The entire Expose To The Right crowd would disagree with you that the current design is sufficient.

                                   

                                  Look around this forum.  I'm not the only one who's noticed this sore thumb in an otherwise fine piece of software.

                                   

                                  I welcome others to try the converters they have on tap on image 3608 above and see whether they derive any good color from them.

                                   

                                  -Noel

                                  • 14. Re: Desaturation of Near Overexposure Question
                                    Noel Carboni Level 7
                                    function(){return A.apply(null,[this].concat($A(arguments)))}

                                    Bill_Janes wrote:


                                    However, -H 9 did not work that well with your image:

                                     

                                     

                                     

                                    Ah, but note what mixing 50% of the color from that recovery into the ACR conversion yields...

                                     

                                    Mix.jpg

                                    Certainly more natural and true to reality than going gray.

                                     

                                    This just proves there are possibilities to improve the output.

                                     

                                    -Noel

                                    • 15. Re: Desaturation of Near Overexposure Question
                                      Level 4

                                      Noel Carboni wrote:

                                       

                                      Ah, but note what mixing 50% of the color from that recovery into the ACR conversion yields...

                                       

                                      Mix.jpg

                                      Certainly more natural and true to reality than going gray.

                                       

                                      This just proves there are possibilities to improve the output.

                                       

                                      -Noel

                                       

                                       

                                      "…there are possibilities to improve the output…"  Yes, by PAINTING colors in like you did. 

                                       

                                      Good job. 

                                       

                                       

                                      Wo Tai Lao Le

                                      我太老了

                                      • 16. Re: Desaturation of Near Overexposure Question
                                        Noel Carboni Level 7
                                        function(){return A.apply(null,[this].concat($A(arguments)))}

                                        Tai Lao wrote:


                                        "…there are possibilities to improve the output…"  Yes, by PAINTING colors in like you did. 

                                         

                                         

                                         

                                        I did not PAINT anything.

                                         

                                        Tai, I do not think you are so dense as to not see that the above color combination could have been done programmatically.

                                         

                                        -Noel