Understanding White, Highlight, Shadow & Blank Controls

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I suspect I am over thinking this, but I feel the need to gain clarification on what these basic controls do and how they are reflected in the histogram.

In the Quick Start Guide, on "Figure 53 Lightroom’s Basic panel is designed to be used top-down... mostly", it shows "- Highlights, + Shadows to pull back highlight and shadow detail" and "+ Whites, - Blacks to extend tonal range". The FAQ adds some clarity with "The Highlights slider only adjusts the brighter tones in the photo and barely touches the darker tones" and "Shadows does the opposite, mainly affecting the darker tones in the photo"

Part of my confusion is that when i select one of the controls, the histogram shows a range for each of the controls (very faint overlay). Working left to right the ranges are black, shadow, blank (in the middle no range), highlight then white. The visual implication is that all are affecting tonal range. Here's an image which kind of depicting what I see.

1578061370451.png


My current thought is that white and black affect the horizontal tonal range while hightlight and shadow affect the vertical number of pixels; correct?

Thanks
 
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I have no idea what you mean with the 'horizontal' and the 'vertical number of pixels'. The number of pixels is the number of pixels. Each slider affects a certain tonal range mainly, but because we do not want banding to occur, this also means that the pixels outside of that range will not be completely ignored. That explains why Whites will pull up the brightest pixels, it will start to pull up darker pixels as well the further you move the slider.

Highlights and Shadows are algorithms that do more than simply increase/decrease the brightness of a certain tonal range. The algorithms also look at how many pixels there are. Large areas will be affected more than smaller areas, that is how the details are enhanced. The danger of this is that you will see edge effects if you use a large correction: you will see halos around edges.
 
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The number of pixels is the number of pixels
Except, the pixels will increase/decrease in parts of the histogram as you make adjustments. Doe this mean that the pixels are redistributed?

Highlights and Shadows are algorithms that do more than simply increase/decrease the brightness of a certain tonal range.
Bingo, that was the part I was missing. They are algorithms rather than just tonal adjustments.

The danger of this is that you will see edge effects if you use a large correction: you will see halos around edges.
This was not something I was aware of

Thanks Johan
 
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You've got the main Classic book too Paul. Go on a few pages to the Tone & Presence section starting on page 203 and you can see the effect of the different sliders on the histogram and on a stepwedge and curve diagram too, which might make it a bit easier to understand.
 
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Thanks Victoria. Need to spend more time reading complete sections rather than just searching by keyword. Between you and Johan, I think I got it.

Your Figure 53 in the Quick Start is also very useful.
 
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Except, the pixels will increase/decrease in parts of the histogram as you make adjustments. Doe this mean that the pixels are redistributed?
Of course. Let's say you have 10,000 pixels that are equal or brighter than 220. Now you move the Whites slider to the left, so you decrease the brightness of these pixels. That means that some of these pixels will get a brightness less than 220, so the number of pixels that are 220 or higher will decrease. The histogram will show that.
 
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