tenbach Loc: SW Utah

There are numerous terms that must in some way relate to the histogram..

Saturation - The definitions I read are pretty vague, color purity,no saturation >> shades of gray, etc. Is saturation based on one of the 256 tone levels with only one color present.?? I do not grasp the definition in a quantitative sense.

Hue - Basically the same question.

Luminance - This one seems a bit more intuitive, but

When it comes to adjusting blacks, shadows, highlights and whites in Camera Raw or LR, it is apparent that portions of the histogram are moved left and right. OK with that.

What is the correct term for the histogram horizontal axis luminance, tone levels, brightness????

Apaflo Loc: Anchorage, Alaska

If you change saturation while watching the histogram there will certainly be a change there too. But you'll never manage to coorelate the two to a degree where you can watch only the histogram and make a useful adjustment judging by the change in the histogram.

The same is true of hue.


With luminance there are at least two specific characteristics that can be judged better by looking at the histogram than from viewing the image itself. How bright the highlights are and how dark the shadows are is easily set looking at the histogram, and much more difficult without it. Contrast is pretty much best adjusted with both a view of the image and while watching the histogram.


Yes.

The two single most important things to know when working with the histogram is that any value higher than 245 may well have detail (differing values from 246 to 255) but few paper prints or computer monitors will be adjusted to really show that detail. It will look washed out. The most significant example where that information is useful is in adjusting levels on a portrait. Any "shine" on checks or other skin areas will be washed out if it is above 245, but can show detail if it is less.

At the other end, in the shadows... It varies depending on the monitor but most will not show anything but pure black below 10, and might not show any useful detail below 20. So deep shadows can go down to 0 or 20 or inbetween. But to see any detail the values need to be higher than that.

And if you buy a really good monitor that has a 1:1000 contrast ratio, keep in mind that the average monitor might be 1:200. And paper will also almost always be far less than what your nice monitor can show.

floral43

Scientific explanation of a histogram is thus:
A statistical, graphical representation showing the relative numbers of variables over a range of values. Dynamic range
In plain English! in this case starting at black max 0 white 255 and all gray tones in between.
Levels control in photoshop show a representation in the form of a histogram.
The threshold command gives you a visual numeral representation as well.
by adjusting the level control you are affecting the range from 0 to 255, that could be a problem and lead to combing,(clipping).
where the threshold command shows that range with out causing damage. understanding the histogram is a great place to start. i like to think of it as a light bar graph.
Hue is the purity of color (wave lengths). how that applies here, say for example only! You have a approx pure red and you want to change that purity you can add gray by % factors and change that purity, this called saturation. you have the hue and saturation control in ps. to test this.

luminance
Phisics, ratio of the luminous flux emitted by an object to the total radiant flux expressed in lumens per watt.
plain english
the luminance in intensity of any surface per unit of projected area of the surface as viewed in a given direction (angle) the reflected light off the surface area, can be measured.can be referred to as brightness (Intensity).
HSB color represented in PS is Hue saturation and brightness.
adjusting blacks, whites and shadows will definitely effect the histogram.
In fact brightness control can causing combing affect. and limit the true dynamic range, by rearranging the darker tones of gray. Clipping.
By moving the controls your effecting the histogram.