Levels tool - output levels
Most levels tool tutorials glaze over the explanation of input and output levels, as if this was basic knowledge that every person posseses by default - from what I understand, output levels constrain the tonal range of ie. black and white pixels in the image, meaning that moving output levels up on the left hand side of the tool will increase the lightness of all dark spots in the image, because any absolute black pixel would be mapped to this new value.
What I don't understand is that, even if I am doing this, how can there still be spots in the image with an RGB value of 0,0,0,0?
As you can see in the image above, I moved output for black to a value of 2. Yet this does not seem to affect certain parts of the image.
Same issue on the other end of the histogram:
My interpretation of this levels setting is: map any pixel above the value of 150 to a value of 244. I moved the output levels on the right hand side down because all the sunlit spots in the image were clipping. Which doesn't seem to affect the selected pixel.
What am I misunderstanding here?
-
My understanding is that what by setting the values to 2,2 and 244,150, you are asking C1 to discard any data below 2 and above 224, additionally C1 will map pure black to 2 and pure white to 150. Essentially, you are compressing your histogram and loosing detail in both the shadows and the highlights.
I would go back to 0,0 on the left, and, judging by your histogram, somewhere around 244,200.
0 -
I've been doing some experiments on this. And then at the end of this response I have an idea about why you are still seeing 0,0,0,0 and 250,250,249, 250 with your settings.
My experiments
Here is one of the few images I could find with both pure black (0,0,0,0) and pure white (255,255,255,255). First with no levels adjustment. Note that the lower two readouts are shown as 0,0,0,0 and 255,255,255,255. (Though see below - they may not be completely black and completely blown out because of the dynamic range of the camera sensor.) The upper two readouts are close to pure white and close to pure black, but not actually a 0 or 255.
If I pull in the lower handles (the input levels) as shown, I can get to the stage where the two upper ones get to 0,0,0,0 and 255,255,255,255 if I pull the inout handles in far enough. I have set the highlights input handle so that everything from 221 upwards becomes pure white, and everything from 12 downwards becomes pure black.
If, conversely, I pull in the upper (output handles) I find that the colour readouts do change. Now the lower spot that was 0,0,0,0 in the heron's eye that was put black is rendered as a dark grey (22,21,22,22) because I have specified that was 0 should be rendered as 17. And what was pure white is to be rendered as just a bit less than that, at 231. (So why are the readouts not actually 17 and 231? I am not 100% sure but I think that it's because of the dynamic range of the sensor of the camera. From 0 to 255 is just 8 stops. At ISO 400, which this was shot at, the Nikon Z8 has a dynamic range of just over 12 stops. So it may be that while 255 is to be pulled in to 231, some of what was slightly beyond 255 is being pulled in to slightly more than 231.)
Your settings
In your screenshots you have the lower left handle at 2, and the upper left handle at 2. That means that 2 in your input image will be output at 2. Should we not therefore expect that 1 would be output as 1 and 0 would be output at 0?
Similarly, at the other end of the histogram, you have 150 on the lower handle and 244 on the upper handle. That means that everything at 150 will come out at 244. But what about something that is at more than 150? Wouldn't you then expect something at, say 160 to be output at more than 244?
Hope that all makes some sense!
Ian
0
Please sign in to leave a comment.
Comments
2 comments