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Why does auto-levels cut some of the data ?

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33 comments

  • BeO
    Top Commenter

    You mean because the difference between the blue and the others channels now is smaller? But I assume the levels stretched the tone distribution in other areas, namely the midtones.

    As does every contrast or curves adjustment, it stretches the tones in one part and squeezes it in another. The question, is there enough detail left where you want to have it.

    If you don't like the resulting images from the auto levels tool, you can change the auto levels behavior in the preferences.

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  • Claude CAUWE

    Hmm, no. Let me make a screenshot:

    You see that at the right of the "lever", there is still indication of pixels.

    The lever now "closes" at 247 after applying "auto-levels", leaving data out.
    Shouldn't it "hug" closely the highest value (as PhotoShop does) ?

    PS: I precisely "maxxed out" the preferences to 0 and 255 to be sure it doesn't clip anything that would prove useful.

     

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  • BeO
    Top Commenter

    In the preferences, the exposure warning is only for the coloration of very bright or very dark pixels. I mena the auto levels thresholds.

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  • BeO
    Top Commenter

    I'm not at my desk but can post a screenshot later

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  • Claude CAUWE

    Did I miss an auto-level threshold somewhere ?

    That would of course explain a lot.

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  • BeO
    Top Commenter

    But I wouldn't get too obsessed with every pixel in the image getting clipped, depending where the highlights are and how important they are for the image, there is a trade off in not stretching the histogram thus far, i.e. it is less stretched, flatter...

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  • BeO
    Top Commenter

    Yes, look int the preferences, I think the tab is called Exposure, anyhow, you'll find it

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  • Claude CAUWE

    Well, yes, that where i have set the high 255 and low 0.

    If you mean this one ?

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  • BeO
    Top Commenter

    Yes, the auto levels clipping thresholds. Play with it, I have them on default. I tweak the important images manually, after I use the autoadjust, anyway, because every image is different.

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  • Claude CAUWE

    yes, thank you BeO for the tip.

    Will check if that helps in some way.

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  • Ian Wilson
    Moderator
    Top Commenter

    If you wanted to clip absolutely nothing, I think you would have to set the Auto Levels Clipping Thresholds to Zero too.

    See the explanation here. https://support.captureone.com/hc/en-us/articles/360002603537-Modifying-Auto-Levels-clipping-thresholds 

    Ian

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  • Claude CAUWE

    Indeed, I saw that, thank you.

    And that brings me another question: why would I clip ?
    Is there a specific reason why one would want to lose a certain amount of data and of dynamic range ?

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  • BeO
    Top Commenter

    You ask very good questions. 

    I think the 2nd sentence in the article gives a high level answer:

    This prevents those few pixels from adversely affecting the rest of the image in terms of contrast and tone.

    My answer would have been similiar, the human eye ist most sensitive in the midtones, although of course it can adapt to different light levels. To account for this, you typically increase the contrast , or you do a typical contrast increasing curve adjustment in S form, you mainly stretch the midtones and squeeze the lower and upper end of the tonal range. That is for even increase differentiation where the brain/ eye is most sensitive, because that is the most important range for humans.

    Stretching the tonal range mainly for the midtones on a slight expense in highlight and shadow differentiation can be advantegeous, of course depending on image content and artistic intent.

    There is no rule which should not be broken at times.

     

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  • Claude CAUWE

    BeO,

    Thanks again for your answer.
    I am late in replying because I wanted to play around a bit before getting back here.

    Setting the Clipping Thresholds to "0" visually decreases contrast and increases "smoothness" of soft light -of course, everything can then be fine-tuned again with the normal "contrast" tool - with a better precision. 

    So my settings will stay on "0" from now on, I guess.
    But as you mention, this is a personal choice.
    Thank you anyway for opening my eyes :-)

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  • BeO
    Top Commenter

    Very welcome.

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  • Ian Wilson
    Moderator
    Top Commenter

    I think that the only trouble with setting clipping threshold to zero could mean that just one over-bright pixel or over-dark pixel could presumably stop the levels from being set to what they would otherwise be and what would make the contrast look right. 

    The alternative is to have a very small threshold. 0.05 percent, for example would allow 1 pixel in 2000 to be overblown. If that doesn't look right, they can be toned down with the highlight or white slider (or conversely the shadow or black slider). 

    It seems odd to allow just a pixel or two to change the overall look of the image.

    Ian

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  • Claude CAUWE

    well, the eye is the final judge ...

    this setting is more for a first "trim"

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  • BeO
    Top Commenter

    Claude,

    If I am reading you right you like a rather "conservative" starting point and develop your images from there.

    If this is the case you might want to try setting the Curve in Base Characteristics to "Linear" (maybe even as the default for your camera), which gives you a rather flat starting point but (should) give you more control over contrast and color with the C1 tools.

    There are users who absolutely favor this approach over the default or other curves.

    I haven't used the Linear curve so often yet, but will do more often in the future to see if that approach is something I like.

     

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  • Claude CAUWE

    I tried that indeed with older pictures from my D300S.

    The result is surprizing, but i cannot say I disliked it.
    Only the idea to re-work all my 40k files put me off :-)

    But I will definitely give it another try with D5 files.
    The day I will be able to use C1 the same way I used Capture NX2 from Nikon, I will be a happy man :-)

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  • Claude CAUWE

    Here is some illustration:

    • File as is from the Nikon body, linear response

    • File as is from the Nikon body, C1P Standard Film curve

    • File as is from the Nikon body, linear response, edited

    • File as is from the Nikon body, C1P Standard Film curve, edited

    I will not post my impressions here to not influence your judgement, but would love to have your opinion.

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  • BeO
    Top Commenter

    I like the image.

    The first two images as expected.

    No.3 and 4 differ mainly in contrast, in my view. Which one looks better is in the eye of the beholder.

    No.3 look a bit more natural. The higher contrast of no. 4 thouhh helps to separate the close-by cheetah stand out more, in this particular image. With a little tweaking of the curves tool they can be made more or less identical.

    Which tools did you use for editing and how well did you feel they behave?

     

     

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  • Claude CAUWE

    Thank you for your appreciation and your comments.

    I fully agree with you. Starting from the Linear Response gives a more progressive, softer look with more nuances, without a lot of work. It gives the impression of a wider palette of colors.

    Her below the tools used:

    • Picture 3: File as is from the Nikon body, linear response, edited

    • File as is from the Nikon body, C1P Standard Film curve, edited

    I haven't used any curve at all.

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  • BeO
    Top Commenter

    Yes, it is easier to make subtle changes.

    Btw, good white balance out of camera.

    Which Nikon body and lens is this shot with?

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  • Claude CAUWE

    I think that the amplitude of the sliders movement in the Linear Response makes it easier to achieve more subtle changes.

    The gear is a Nikon D5 and the Nikon 200-500 f5.6 zoom (a true bargain at 1300 euros new !)

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  • BeO
    Top Commenter

    I have the 300mm f/4D IF ED and TC1.4 II for a few hundreds more but think it might not have been my best buy, too short, not very sharp at f/4, no VR, Bokeh so la la. With the Z7 on my this-year wish list at least the VR issue will be solved.

    Maybe your zoom is worth testing, I didn't know it is such inexpensive.

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  • Claude CAUWE

    Hahaha, I had the same 300 as you.

    ought it 2nd hand and used it so much that paint is completely gone.

    For the rest, everyone has different needs, of course.

    But with a constant 5.6, for me, the 200-500 really does the job - especially at that price (quite incredible that Nikon sold such a long lens at such a low price !)

    Sharpness is pretty acceptable as well - as seen from the much-cropped pict - crop factor being recognizable by the infamous non-scalable watermark :-)))

    What body do you use ?

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  • BeO
    Top Commenter

    Funny!

    Yes, sharpness of your 500 is very acceptable. This is an amazing colorful little bird!

    I searched a little bit the internet and found people reporting a high sample to sample variation of this lens? Maybe you are lucky and have a good copy?

    My camera body was a D7100. Fresh from the camera store, I had to dial in + or -20 for AF fine tune for the 300mm, if I remember right, it was at the end of the value range. Not acceptable for me because what happens if temperature changes, would I potentially need a value beyond the scale? So I brought it to the Nikon service and they adjusted this combination plus another lens, I could use acceptable values then.

    However, I could not find a value which worked for near minimal focus distance as well as for medium ranges. And the firmware did not allow to set more than one value, at least two would be needed to interpolate at all distances to correct those back or front focussing issues which are due to the tolerances of the AF technology inherent to mirrorbox cameras. And, btw., the AF fine tuning procedure itself was a pain in my neck, plus the nessicity to service new camera gear all the time, all bodies and lenses, altogether, as adviced by many.

    I felt the well known camera companies did not do well with their development of AF technology and accuracy to accomodate the improvements in sharpness of shallow depth of field / wide open lenses in combination with high pixel density sensors. Would they have, I would have probably sticked with mirror systems, at least at that time, but this was actually THE reason for me to switch to mirrorless systems.

    I still have the 300mm and use it occasionally dumb-adapted to Olympus and Sony, focussing manually, but it is awaiting a second life with mirrorless Nikon...

    cheers

    BeO

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  • Claude CAUWE

    I heard indeed of these differences from sample to sample.

    Maybe I was lucky ? Brought it anyway to Nikon Service (under warranty) for a check - and they OK'd it.
    Dunno if they fixed something or not, but they never discussed the necessity of the check.

    Getting back to our levels .. I have been reworking some of my pictures, starting with Linear Response, and I must say I am much more pleased with the results than with the C1 results.

    I find back many more nuances - I would say: the Nikon colors are back, while, when compared now, they seemed a bit dull.

    Lots of work in sight ....

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  • BeO
    Top Commenter

    Maybe curves tool? Try also a tiny bit of the clarity "classic". I would wonder if the exact look from Nikon could be replicated though.

    Keep posting if you are a step further, or even if not.

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  • Claude CAUWE

    I am not that much at ease with the C1P curve tool.

    Quite strange, because I felt totally at home with the Nikon Capture NX2 curves ...

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