Fixing Contrast
Most photographic images taken with digital camera’s or scanned in from prints will require at least a small tweak to ensure that the colour and contrast levels are correctly set. Just looking at your image on screen will not guarantee it’s readiness for print, email or website output.
It is far better to get a clear idea of the ‘Levels‘ of your image to make a clearer judgement on whether or not your photograph is at the highest quality. The levels of light and dark, saturation, and colour and tonal depth.
Adobe Photoshop Levels
Adobe Photoshop offers a very useful dialogue box called ‘Levels’. It provides you with the ability to control the contrast, light and dark and colour depth within your image via a histogram of tonal information. In this Adobe Photoshop tutorial, we will be looking at a single method for fixing contrast within a black and white (Grayscale) image.
Excersise: Call up Levels dialogue box
- Open an image, preferably a dull or washed out black and white. Let’s keep this excersise simple to start with and either load up a grayscale image or convert your current image to grayscale by opening the Image->Mode menu and choosing ‘Grayscale’ (see our Color Mode Tutorial for more information). You may be presented with a dialogue box - ‘Discard color information‘ – ‘OK’ this. You can also use the image from this tutorial by downloading it from here.
- Access the Levels dialogue box by either opening the menu ’Image->Adjustments->Levels‘, or by using the quick key ‘CTRL/APPLE L‘ (recommended method).
Now you can see the Levels dialogue box. It may look a little scary if this is your first time with Levels, but there is very little to it.
Excersise: Tweak Levels to correct tonal problems.
Levels - Tonal Range
The black, mountain-like structure in the centre of the Levels dialogue box is called a histogram. This histogram can be described as a bar chart representing a frequency of distribution – in this case, tones from black to white. The high points show a higher presence of a shade along the tonal range. The tonal range is best described by the gradient bar along the bottom of the dialogue box.
In the example image, the histogram levels tell me that my image is mainly dominated by grey shades, nothing in the darker to black or lighter to white. Most photographs with natural light should have plenty of activity in the darker and lighter ends of the tonal range. This image is not at it’s best.
Fig.1 Corrected Levels
To correct the distribution of dark and light – effectively increasing the contrast of our image, I’m going to drag the black point (1) and the white point (3) in until they reach the start of an increase in tonal frequency. By doing so, already you can see that the image is now looking a lot better (Fig.1). It is always a good idea to ensure that the ‘Preview‘ checkbox is checked, so that you can see the results of your tweak as you go along.
Fig.2. Alt Levels
If you require a higher level of accuracy, try holding down the ‘Alt’ key on your keyboard whilst dragging the white or black point. A visual representation of the changes will appear on screen as you move your points in (Fig.2).
Now that the contrast is fixed, we can now turn our attention to the brightness of our image. This is a very simple fix. Simply drag the ‘Mid’ point (2), either to the left lighten or right to darken.
If you are wondering what the other two points do beneath the tonal range at the bottom of the Levels dialogue box: They allow you to compress the frequency of information further in, reversing the fix that we have just performed and effectively decreasing contrast. This is sometimes useful when deliberately graying out an image or, to a certain degree, reducing contrast.
