Question about Photoshop Levels Tutorial

[purplehaze]

In the following quote from the CiC tutorial on levels, is the part I have highlighted correct? It seems counterintuitive to me.

"Moving the midtones slider compresses or stretches the tones to the left or right of the slider, depending on which direction it is moved. Movement to the left stretches the histogram to the its right and compresses the histogram to its left (thereby brightening the image by stretching out the shadows and compressing the highlights), whereas movement to the right performs the opposite."

[LeoLeo]

Hi Janis,

Yes, it is a bit confusing but the information is right. I will try to make it a bit simpler:
let's consider that we have 9 levels, from black (-4) to white (+4), like below

-4 -3 -2 -1 0 +1 +2 +3 +4 | We have a equal number of black/white values, and consider 0 as "midtones". Now, we are going to move 0 to the left, like so:

-2 -1 0 +1 +2 +3 +4 +5 +6 | The same numbers of total values (9), but only 2 in the "black part" and 6 in the "white part". Having more values to the "white zone", makes the image brighter.

For sure is not the most academic explanation, but hope it helps.

Leo

[purplehaze]

That is what I understand, Leo, so it seems to me that, in yours and Sean's examples (i.e., moving the slider to the left), we are compressing the shadows and stretching the highlights, or just the opposite of what is stated in the tutorial.

[Dave Humphries]

That is what I understand, Leo, so it seems to me that, in yours and Sean's examples (i.e., moving the slider to the left), we are compressing the shadows and stretching the highlights, or just the opposite of what is stated in the tutorial.

Hah, I can see exactly what you mean - to the extent I had to try it

What is written is true, moving the mid-tones slider to the left does lighten an image.

I tend to think of it as saying "I'm moving this to here and I want that to be "the new" mid tone point", so in the output, it puts that in the middle, which stretches the left hand side (of histogram) and compresses the right, making the picture appear lighter.

Have a play with the Black point sliders on both Input Levels and Output Levels scales, it may help you get a better grasp of what is being done when you hit the OK button.

Make sense?

[purplehaze]

Hah, I can see exactly what you mean - to the extent I had to try it

What is written is true, moving the mid-tones slider to the left does lighten an image.

I tend to think of it as saying "I'm moving this to here and I want that to be "the new" mid tone point", so in the output, it puts that in the middle, which stretches the left hand side (of histogram) and compresses the right, making the picture appear lighter.

Have a play with the Black point sliders on both Input Levels and Output Levels scales, it may help you get a better grasp of what is being done when you hit the OK button.

Make sense?

Thanks, Dave. Aperture 3 doesn't have the Input and Output Levels scales, but it has a histogram at the top of the "Inspector" that displays the effects of adjustments and when I watched that at the same time as I moved the mid-tone slider of the Levels brick, light finally dawned and I understood and it was good. Another step taken up the learning curve.