levels : Auto levels
Hi
When doing a auto levels ("A") on levels, the "black point" is always changed to 1 from 0.
Is there a way to avoid it?
I shoot quite some high ISO stuff underexposed (to preserve highlights aka lights or windows) and it's annoying that it moves the "black point" to 1.
Alain
When doing a auto levels ("A") on levels, the "black point" is always changed to 1 from 0.
Is there a way to avoid it?
I shoot quite some high ISO stuff underexposed (to preserve highlights aka lights or windows) and it's annoying that it moves the "black point" to 1.
Alain
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Try the CO 8.2 update. You can set the Auto Levels Clipping Threshold from the preferences, Exposure tab. 0 -
[quote="Paul_Steunebrink" wrote:
Try the CO 8.2 update. You can set the Auto Levels Clipping Threshold from the preferences, Exposure tab.
Thanks Paul, but unfortunlly it doesn't seems to change the problem.
I still get the move to 1 if I use 0% or 0.01% or 0.5% for the shadow threshold.0 -
Hmm, that's a pity. I had hoped it helped. 0 -
[quote="Paul_Steunebrink" wrote:
Hmm, that's a pity. I had hoped it helped.
Me too.
Unfortunately this problem as the auto levels for me not usable, if it could work only on highlights it would save quite some time. And save from dumb work.0 -
[quote="Alain" wrote:
[quote="Paul_Steunebrink" wrote:
Hmm, that's a pity. I had hoped it helped.
Me too.
Unfortunately this problem as the auto levels for me not usable, if it could work only on highlights it would save quite some time. And save from dumb work.
For your purpose - adjust only the level for highlights - whey would be the benefit of using Auto Levels compared to setting the highlight level by itself?
Grant0 -
[quote="SFA" wrote:
[quote="Alain" wrote:
[quote="Paul_Steunebrink" wrote:
Hmm, that's a pity. I had hoped it helped.
Me too.
Unfortunately this problem as the auto levels for me not usable, if it could work only on highlights it would save quite some time. And save from dumb work.
For your purpose - adjust only the level for highlights - whey would be the benefit of using Auto Levels compared to setting the highlight level by itself?
Grant
It's more than one picture. After first culling with "fast raw viewer" I often import between 100 and 1.000 pictures that are -on purpose- between 0.7 and 3 stops underexposed to preserve the highlights. A first auto levels on all pictures makes the workflow a lot faster.0 -
Hi,
not sure if I got it right what you intend to do. If you want to do an Auto Adjustments on the imported images you can do that with "Levels" on or off. For some time I did that with Levels on but I didn't like the results and switched Levels off for the Auto Adjust. If you have Levels executed as one step of Auto Adjust then you could reset the Levels by simply marking all the reffering images and press the Reset icon on top of the Levels tool section. This however resets black and white point.0 -
So what does the new "auto levels clipping threshold" that Paul referred to really do? I haven't been able to work that out yet.
Ian0 -
[quote="Ian3" wrote:
So what does the new "auto levels clipping threshold" that Paul referred to really do? I haven't been able to work that out yet.
Ian
Ian, if you do an Auto Adjust on the Levels tool (the A symbol in Levels' header), the black and white point will move to a level that the image start clipping. This is best illustrated with a low contrast image that easily fits in the 0-255 range.
By default CO8 allows a certain percentage of pixels to be clipped (0.10%). This is an average which works fine for most images. But photographers want control of automatic adjustments. Some allow more clipping, some less. This is where the adjustable threshold comes in.
You can easily test and try yourself. Take an image (again, low contrast might work best for demonstration) and apply Auto Levels. Make a few clone variants. Now, change the threshold in the preferences and apply Auto Levels on the second variant. Change threshold again, go to third variant and so on till you get bored. 😉
Note that the higher the threshold, the more pixels will get clipped (you can also set exposure warning on for both highlights and shadows).0 -
Thanks, Paul - I'll have a look at that and try out the different settings. But from your description, you would think that setting the clipping threshold to zero should mean that the shadow slider should not move from 0 to 1 if the shadows are already clipped, shouldn't it?
Ian0 -
[quote="Ian3" wrote:
But from your description, you would think that setting the clipping threshold to zero should mean that the shadow slider should not move from 0 to 1 if the shadows are already clipped, shouldn't it?
Yes, that would make sense if the shadows are already clipped.0 -
[quote="Paul_Steunebrink" wrote:
[quote="Ian3" wrote:
But from your description, you would think that setting the clipping threshold to zero should mean that the shadow slider should not move from 0 to 1 if the shadows are already clipped, shouldn't it?
Yes, that would make sense if the shadows are already clipped.
I did check again and with a lot of clipped blacks the slider stays on zero. I think that the blacks that I see are in reality not clipped, but very very close to it. I also suspect that the 0 and 1 are rounded 8 bit values that are shown and that 16-bit values are used in the engine.
After looking very carefully I have also the impression that the image changes less than before if the slider changes van 0 to 1.
I often still see rather big changes on the whole histogram if the value goes van 0 to 1, I see changes up to the top quarter.
I suspect having a camera with a rather big dynamic range has it's disadvantages 😉0
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