9 Replies Latest reply on Jan 2, 2014 7:19 AM by the_wine_snob

    'Auto Levels' effect - What exactly is it doing?

    Pbeck1 Level 1

      I'm quite new to video editing & making some home movies. I'm looking for an easy way to brighten (and color correct) my indoor video clips that have been shot under poor lighting, so they look as good and bright as the ones outdoors. It would be great if all clips along the movie were roughly the same brightness and didn't contain nasty color casts.

       

      I'm interested in the 'Auto Levels' effect for this but I'm unsure as to exactly what it does. To me it looks like it's a tool to brighten those dark clips up to their ideal level and to remove those color casts, and if so it's exactly what I'm looking for.

       

      However, In the help file (Pre10) it says:

       

      Auto Levels automatically corrects the highlights and shadows. Because Auto Levels adjusts each color channel individually, it may remove or introduce color casts, which are tints to a clip.

       

      What I'm unsure about after reading the help file (above) is this: Is it just effecting only the highlights and shadows like it says? If so, what about the mid-range of tones (sorry but I'm used to using Lightroom, lol). My guess is that it is actually stretching each color channel to it's dark and bright maximum, and thus brightening the levels universally across all tones, and at the same time removing color casts. So my confusion is why the help file just says highlights and shadows.

       

      Could anybody help me to understand the effect better?

       

      Also, is there an ideal standard level of temporal smoothing to remove those sharp changes, ie one that fits most clips fairly well?

        • 1. Re: 'Auto Levels' effect - What exactly is it doing?
          N9JCR Level 2

          I can't answer most of your specific questions about how exactly it works, however I can say I've tried it in previous releases and it introduced problems in the video that were worse than what I was trying to fix..  Auto Levels caused the brightness/contrast to lighten and darken every few seconds, aparently as it was sampling the video frames.  The introduced effect was obvious and annoying.  Now perhaps in newer versions it's better but I've had more consistent results setting brightness and contrast individually and manually.

           

          It may be best to experiment with the different options and see what works for you.

           

          Hope that helps!

           

          Bob

          • 2. Re: 'Auto Levels' effect - What exactly is it doing?
            Pbeck1 Level 1

            Yes, I think after having a play with all the effects I'm starting to agree with your findings too. I may just stick to using the brightness and contrast method. Its not perfect though as it nicely brightens dark parts of the clips but you just have to hope the camera doesn't turn into any bright areas. I think I want to leave the auto effects alone.

            • 3. Re: 'Auto Levels' effect - What exactly is it doing?
              the_wine_snob Level 9

              The Auto Levels Effect can be useful IF the scenes, to which it is applied, are identical in lighting, and exposure. If, however, the scene has changing lighting, or changing exposure, one can get "strobing," as the Effect tries to correct each. Personally, I prefer to do CC, and other adjustments manually, with say the Three-way Color Correction.

               

              Some editor do like the Auto Levels Effect, and might Cut a longer scene, at points where things change. This can help eliminate the "strobing" effect. Still, I like to do things manually, so that I have more control. I might still Cut longer scenes, so that my manual Effects can be applied to just that portion of the longer scene.

               

              As with Ps and LR, the Auto Effects (Filters in those Image editing programs), might be just what is needed, but I more often work in Curves, or Levels, to manually make my Image adjustments. When Auto ___ works fine, great, and when not, then I go to manual mode.

               

              Good luck,

               

              Hunt

              • 4. Re: 'Auto Levels' effect - What exactly is it doing?
                Pbeck1 Level 1

                Bill, thanks for your great advice

                • 5. Re: 'Auto Levels' effect - What exactly is it doing?
                  the_wine_snob Level 9

                  You are most welcome.

                   

                  Good luck, and happy editing,

                   

                  Hunt

                  • 6. Re: 'Auto Levels' effect - What exactly is it doing?
                    Pbeck1 Level 1

                    As two alternatives to the 'auto levels' effect, I've been playing around with the brightness/contrast effect and  also the exposure slider in the 'auto tone and vibrance' effect.

                     

                    Are my finding below right?

                     

                    In PreE 10 i did tests using a greyscale image with various increases in either brightness or exposure, screen grabbing the results of a frame for each and measuring the brightness increase along the scale of the greyscale image.

                     

                    Lets say we are trying to brighten a clip.

                     

                    The brightness effect brightens all pixels by roughly the same amount (whether they are dark or bright to begin with), thus shifting the entire histogram to the right. This includes clipping the high values if the image becomes too bright. Contrast is thrown out because we no longer have blacks in the image, and thus some kind of contrast adjustment is then also needed.

                     

                    The exposure effect however effects the mid range tones the most and the darkest and brightest tones the least. This means far less clipping in the brightest areas during brightening, and the darkest areas stay seated. Contrast adjustment is still needed if the mid tones are compressed into the brighter tones &/or the darker tones are no longer dark enough (i suppose you could lower shadows instead but i never played around with that idea).

                     

                    Does that sound about right (or not)?

                    • 7. Re: 'Auto Levels' effect - What exactly is it doing?
                      the_wine_snob Level 9

                      Pbeck1,

                       

                      Yes, those observations do seem correct to me.

                       

                      There are also two other Effects, that I use a lot - Shadow & Highlight and 3-way Color Corrector. What I do not remember, however, is if those Effects were included in PrE 10 - your version.

                       

                      Once, PrE's Shadow & Highlight did not offer full manual settings, and it was more "Auto." Also, I do not recall just when 3-Way CC was added. I would urge you to investigate those, if you have them. Do not let the "Color Corrector" aspect of 3-Way CC cloud your thinking, as it can do much more than correct color. It works a bit like Curves (in Photoshop), but with even more power. One can use it to adjust density, and other aspects, leaving the actual color alone. IF it is available in PrE 10, you will have a lot of correction power, right at your finger tips.

                       

                      When I am doing color grading, in PrPro (which has Shadow & Highlight, with full manual control, if "Auto" is unchecked, plus additional CC Effects), my normal workflow is:

                       

                      • Apply Levels (manual only)
                      • Apply Highlight & Shadow (manual only)
                      • Apply Fast Color Corrector, or the more powerful 3-Way CC
                      • Tweak each, as is necessary
                      • Render Timeline to fully process those Effects
                      • Study the results critically

                       

                      Remember, the order of applied Effects CAN affect exactly how they interact on a Clip, so do not hesitate to experiment with the order of the Effects. For me, the above order works fine for most Clips.

                       

                      Good luck,

                       

                      Hunt

                      • 8. Re: 'Auto Levels' effect - What exactly is it doing?
                        Pbeck1 Level 1

                        Thankyou for your valued help

                        • 9. Re: 'Auto Levels' effect - What exactly is it doing?
                          the_wine_snob Level 9

                          You are most welcome, and hope that helps,

                           

                          Let us know if you have any additional questions, or need clarification.

                           

                          Good luck and happy editing,

                           

                          Hunt