Levels with DigitalCreative.info's Guide to Digital Photography and Image Manipulation

When you first open your image files from the camera don't immediately think, "Right .......... I'll print that!" Firstly, examine it closely and consider the ways in which it might be improved. Does it have good contrast? Are the colours well saturated? Does it contain unwelcome elements (eg. lamp - posts growing out of heads!)? Is the subject surrounded by unnecessary detail? All of these are questions to be asked and then answered. You can click on the 'Enhance' button in the menu bar, which will open a box allowing you to ask the software to take charge and make the adjustments for you but it's more fun to do them yourself! Let's take them in turn.

1. Let's look at contrast first. (We'll assume that you've already done any sharpening and high pass that is needed). If it still seems rather flat or the colours quite drab, when they should be brighter, try a levels layer first. Open the layers palette and, at the bottom, click on the 'create new fill or adjustment layer' icon and open a 'levels' adjustment layer.

2. This will open a histogram showing the distribution of tones throughout the image:

This histogram shows that there is a full tonal range, full of contrast, with the possibility that some of the detail in the lighter areas has been lost, making them completely white, as there is a 'spike' at the right-hand end.

3. The next histogram tells a different story ......... there are strong whites and blacks with plenty in the mid tones but it lacks any real drama. Let's look in more detail at what it tells us ..............

The levels box opens to show that the channel is RGB - in other words it adjust all the colour channels equally. It is possible to open the drop down menu and select an individual channel to adjust but, for our purposes at the moment, RGB is fine. The box displays 2 scales: the histogram which works with the input levels, and the output scale with its own slider from black through all the tones to white.

Looking at the input scale the 0 represents absolute black (ie no detail), and the left hand slider regulates it; 255 represents absolute white (ie no detail) and the right hand slider regulates it; all the numbers in between are the grey tones and the middle slider regulates these.

4. Making our adjustments on the same image we can see what happens when the left hand slider is moved to the right ..... all the tones with a value of less than 128 (the left hand input value) become black. (The mid tones slider moves in conjunction and remains at 100)

5. In the next picture I've returned the black slider to where it belongs and pulled the left hand, whites, slider towards the left. Everything with a tonal value between 125 and 255 has become white.

6. In the next picture I've adjusted the blacks and the whites but I've also moved the mid-tones slider to the left, giving them a value of 2.47, (and making them lighter) to create a very contrasty image. Notice how the levels commands affect the colours and the saturation.

7. The lower, output, slider should be treated with caution as it regulates blacks and whites. Only use this slider if you need the 'flat', lacking contrast, effect that it creates. If the two sliders remain at 0 and 255 then blacks will be black and whites white. If you move the left hand slider to the right then the value you choose will be that to which anything with a lower value will resolve ie. the blacks will beome grey. If you move the white slider then pure whites will be lost and become grey. In the two examples below the first one has the right hand slider, affecting light values, moved to the left, from 255, to a value of 180. The second one has the left hand slider moved from 0, to the right, to a value of 105. You don't need to remember the numbers! Just open the layer, experiment and explore the possibilities.

8. The option to use the output slider has its uses when you wish to 'screen back' the background (on another layer) behind the subject, as shown below:

9. When using the levels adjustment layer your histogram should just touch the absolute black and white sliders. If they don't then the image will appear 'flat', as in the first picture, below. If this is the case, drag the sliders to meet the histogram limits and see the contrast increase, as in the second picture:

10. Usually we're trying to introduce contrast and 'life' into our image but be careful not to 'bleach' out light areas or lose detail in dark areas. Inspect it closely with the zoom tool and undo in edit, or the history palette.