This tutorial will show you the best method for improving the contrast and light quality of any black and white image. You’ll be amazed by the results.
Most photographic images will require at least a small tweak to ensure that the contrast or colour levels are correctly set. Just casually viewing your image on screen will not guarantee it’s readiness for print, email or website output.
Adobe Photoshop Levels
Adobe Photoshop offers a very useful tool called the Levels dialogue box. It allows you to control contrast, light levels and colour depth via a histogram of tonal information.
Step 1: Call up Levels dialogue box
- Open an image, preferably a dull or washed out gray-scale. Let’s keep this exercise simple and either load up a gray-scale image or convert your current image to gray-scale by opening (menu)->Image->Mode and choosing ‘Grayscale’ to discard colour information. (See our Color Mode Tutorial for more information).
- Access the Levels dialogue box by either opening the (menu)->Image->Adjustments->Levels, or by using the quick key CTRL+L. You can also apply levels as part of an Adjustment Layer.
Step 2: Tweak Levels to correct tonal problems.
The black, mountainous structure in the centre of the Levels dialogue box is called a histogram. It representing the frequency of distribution of tones from black to white. The high points demonstrate greater quantities of each tone as it passes from black to white across the tonal range.
In the example image (right), the histogram levels clearly demonstrate that this image dominated by grey shades. This is no information at either the black or white end of the tonal range. Most photographs with natural lighting, should have plenty of activity in the darker and lighter ends of the histogram.
To correct this distribution issue, we will need to stretch our ‘mountain’ of tonal information, from the dark to the light end of the tonal range. This will have the effect of increasing the contrast as more pixels are converted to black or white.
To do this, drag the black and white points in until they reach the start of an increase in tonal frequency. Ensure that the Preview box is checked, so that you can see the results of your actions.
If you wish to finely tweak your Levels to get the very best result, try holding down the ALT key 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).
The aim here is to retain as much detail as possible. As you drag with ALT, you’ll see the fall-off as information starts to appear. Try and place your pointer at the point where the fall-off is no more that small specks of information. If you push it inward to the point where clumps are starting to form, then you have gone too far. Draw back a little as you don’t want to loose pixel detail in either the black or white areas of your image.
This is very straight forward. To increase the brightness of your image using Levels, you simply drag the mid-point (gray slider) to the left. To darker your image, drag it to the right.