Levels tool oddity (?)
There's something in Levels tool behaviour that I can't understand. I'm used to Photoshop levels and I expected CO to do the same. Beneath the histogram there are the black and white sliders to set the input (or clipping) values while the relative sliders above it set the output levels and should remap the input values to these.
So, for example, I expected that setting the black input value to 128 would clip everything below (indeed that's what happen) and consequently setting the black output value to 128 too would brighten and remap all the clipped areas to grey (that's what happen in PS and makes completely sense). Instead raising the output to the same value of input brings back the image to the original appearance. I mean that setting them both to the same value (be it 0, 40, 80 or 128) has no effect on the image. Nothing gets clipped and nothing gets remapped as if the sliders forget their "black-ish" essence and become just an unaltered random point on the curve tool. In my opinion this does not make sense. The same applies for white input and output sliders of course.
If you do the same in the Curve tool, I mean if you drag the black anchor point to input 128 and output 128, everything works as expected. Everything below 128 gets clipped and turns grey.
About black and white anchor points in curve tool the manual states: "They enable you to set black and white points (remap the darkest and lightest values in the tonal range), like the Levels tool." but actually Levels tool doesn't work the same way, at least not entirely. With Levels tool you can clip or you can remap but you cannot do both at the same time or they will cancel each other. Is anybody aware of this and why Levels tool works this way?
So, for example, I expected that setting the black input value to 128 would clip everything below (indeed that's what happen) and consequently setting the black output value to 128 too would brighten and remap all the clipped areas to grey (that's what happen in PS and makes completely sense). Instead raising the output to the same value of input brings back the image to the original appearance. I mean that setting them both to the same value (be it 0, 40, 80 or 128) has no effect on the image. Nothing gets clipped and nothing gets remapped as if the sliders forget their "black-ish" essence and become just an unaltered random point on the curve tool. In my opinion this does not make sense. The same applies for white input and output sliders of course.
If you do the same in the Curve tool, I mean if you drag the black anchor point to input 128 and output 128, everything works as expected. Everything below 128 gets clipped and turns grey.
About black and white anchor points in curve tool the manual states: "They enable you to set black and white points (remap the darkest and lightest values in the tonal range), like the Levels tool." but actually Levels tool doesn't work the same way, at least not entirely. With Levels tool you can clip or you can remap but you cannot do both at the same time or they will cancel each other. Is anybody aware of this and why Levels tool works this way?
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[quote="ClauS" wrote:
There's something in Levels tool behaviour that I can't understand. I'm used to Photoshop levels and I expected CO to do the same. Beneath the histogram there are the black and white sliders to set the input (or clipping) values while the relative sliders above it set the output levels and should remap the input values to these.
So, for example, I expected that setting the black input value to 128 would clip everything below (indeed that's what happen) and consequently setting the black output value to 128 too would brighten and remap all the clipped areas to grey (that's what happen in PS and makes completely sense). Instead raising the output to the same value of input brings back the image to the original appearance. I mean that setting them both to the same value (be it 0, 40, 80 or 128) has no effect on the image. Nothing gets clipped and nothing gets remapped as if the sliders forget their "black-ish" essence and become just an unaltered random point on the curve tool. In my opinion this does not make sense. The same applies for white input and output sliders of course.
If you do the same in the Curve tool, I mean if you drag the black anchor point to input 128 and output 128, everything works as expected. Everything below 128 gets clipped and turns grey.
About black and white anchor points in curve tool the manual states: "They enable you to set black and white points (remap the darkest and lightest values in the tonal range), like the Levels tool." but actually Levels tool doesn't work the same way, at least not entirely. With Levels tool you can clip or you can remap but you cannot do both at the same time or they will cancel each other. Is anybody aware of this and why Levels tool works this way?
Does this short video throw any light on what you are seeing?
https://www.youtube.com/watch?v=NQiqOinqHV4&t=177s0 -
Isn't the tool doing exactly what you have asked it to do? if you set both input and output to, say, 40, you are setting it to make sure that 40 input comes out as 40 output, which will look much the same as asking 0 input to come out as 0 output. I don't use PS, so I am not sure fully how it works. But it looks as though you are right that it does not do the same thing as far as the output levels are concerned. Whether one is more logical than the other is hard to say: perhaps it is a matter of which you are accustomed to.
Ian0 -
[quote="IanS" wrote:
Does this short video throw any light on what you are seeing?
https://www.youtube.com/watch?v=NQiqOinqHV4&t=177s
No, it doesn't. It's an explanation on color balancing a picture with levels tool, but interesting anyway.[quote="Ian3" wrote:
Isn't the tool doing exactly what you have asked it to do? if you set both input and output to, say, 40, you are setting it to make sure that 40 input comes out as 40 output, which will look much the same as asking 0 input to come out as 0 output. I don't use PS, so I am not sure fully how it works. But it looks as though you are right that it does not do the same thing as far as the output levels are concerned. Whether one is more logical than the other is hard to say: perhaps it is a matter of which you are accustomed to.
Ian
Let's put it this way:- If you set black input value to 40 you expect black to clip at 40 and that's it.
- If you set black output to 40 you expect black to be mapped to that value and that's it.
- Setting them both to 40 I expected both of these things to happen simultaneously (as in PS) but that's not the case.
I expected the sliders to act like taking the black anchor point on Curve tool and dragging it to 40,40 position and not like creating a new 40,40 point on the curve. Instead if you move both the upper and lower sliders it's exactly like creating a new point and dragging it around. Thinking about it in the sense of linear response is logic, but make sense to me only if you let go the sliders relation with black and that's not what their color and names imply. This is my logic.0 -
If, in the Levels tool, you "fix" the centre points rather than allowing them to float to a mid point you may see the results you are expecting. 0 -
[quote="SFA" wrote:
If, in the Levels tool, you "fix" the centre points rather than allowing them to float to a mid point you may see the results you are expecting.
Could you please explain further? I do not see them or I do not understand what you mean.0 -
I've made a screenshot to be sure I make myself clear.
https://ctxghq.am.files.1drv.com/y4mLEFxhol4L9Oobsyog85WQktPJv_-W49_xudnu4L8DM_yH3cRPs5DxxHRSKLxFvZJlxCm9vPOPpZpXGddZQta2L0rKVQz4i-XKpvZal-LWXn67OB9hxxQ3XFxgk6F3j26qzYLmVefCzTo-NKgoCz5e2b577nckilQwP1YNnx9-OeGhQ2kcPE7tL2ReP_eYiBb0RdMdFr68wh_W__NxAjkwg?width=660&height=433&cropmode=none
This forum can't display it at full size. You can see or download it from here0
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