One of the simplest way of giving a photograph lift is by checking and if necessary, adjusting the levels. This involves taking a peek at the histogram of the image. Do not be perturbed by the word 'histogram'. It is very easy to understand, evaluate and adjust.

In general, the histogram will tell you if the exposure balance of the photograph is reasonable or not. So, what is a histogram? Basically it is a graph of the amount of data the photograph contains. It is very simple to understand, as the following mini tutorial will show.

This tutorial is based on using Photoshop but the same techniques apply to any imaging software where the adjustments of levels is available. In Photoshop, the Levels Pallet is accessed on the top menu: Image --> Adjustments--> Levels. The hot-key shortcut to the levels pallet is Ctrl+L.

In this example, the following photograph is one of a craftsman re-caning a chair. It is a little dark and lacks contrast & life.

Fig 1: The original dull, lifeless image

Opening up the levels pallet reveals the graph (histogram) of the exposure state. Before we go on to do the adjustments, it is worth noting certain aspects of the pallet. First of all and for the purpose of this tutorial, you can ignore everything on the pallet except the graph, the three little slider handles and the OK/Cancel buttons. Make sure that the Preset box is set to 'Default' and the Preview box is checked.

Fig 2: the original showing the levels pallet and the histogram

The things to note and understand are labelled A, B & C. Point 'A' is the darkest area on the photo and point 'B' is the lightest area. The width of the graph, 'C', represents the total amount of data that the image holds. Taking note of the 'x', 'y' & 'z' points, x represents the black point, y, the mid grey point and z the white point. Here, A is a dark grey and B is a light grey. The overall graph is bunched toward the left. What we need to do it to move the x & z sliders to coincide exactly with the A & B points of the graph as shown in Fig 3 below.

Fig 3: The x, y & Z sliders set.

By setting the x slider to point to the absolute start of the histogram (graph), point A, we are shifting what was the dark grey to a black. Likewise adjusting the z slider to point B, we are shifting what was a light grey to a white point. In other words the darkest part of the original was a dark grey is now a pure black and the lightest was a light grey is now a white.

This has the effect of widening the graph to take advantage of the dynamic range from black to white instead of dark grey to light grey.

Now we come to the slider y. This can be nudged up or down, depending on the object and personal likes. It will lighten or darken the mid grey areas in the image. In this example, the y slider was moved slightly to the right, making the mid range tones a little darker.

Fig 4: The final result from adjusting the levels of the histogram.

Just to show the effect of the adjustments we have done, Fig 5 below, shows a well proportioned histogram whose graph fills the full width from 0 (black) to 255 (white) We have stretched out the original bunched up histogram, giving it the lift in brightness and depth in contrast.

Fig 5: The resulting histogram of the completed adjustment image in Fig 4 above.

Be aware: Adjusting levels is about adjusting the brightness or darkness and contrast of a photograph. It is not about adjusting the colour saturation.

Taking the left (black point) slider into the histogram area will lose shadow detail. Likewise taking the right (white point) slider into the histogram area will blow out the highlights

Now that you have the basic understanding of what a histogram is and how the adjust the levels, believe it or not you are 95% of the way of understanding that dreaded technique 'Curves'!

The primary difference between levels and curves is with Levels, you only have 3 points of adjustment (x,y & z). Whereas with curves, you can have as many as you need. That is going to be the subject of another mini tutorial.

In the meanwhile, I suggest that you open one or two of your own photos and inspect and adjust the levels and see how much satisfaction you get from seeing the difference. Then explore the different presets and the 'Auto' button on the levels pallet.

Ignore the eyedroppers - When used carefully and correctly, they can correct colour casts on an image. Likewise ignore the options button. (At this stage, you don't want to know it.)


© 2011 Donald Gray