The Levels palette is an essential tool when it comes to adjusting highlights and lowlights in a black and white image. The first thing you will notice when you access the palette is the large jagged line that runs from one side to the other. This is called a Histogram.
Histograms are a representation of the tonal range of an image, displayed as a graph with peaks and troughs. From this graphic version of the information you can see immediately where parts of the image are too dark (troughs) or too light (peaks). By using this information, you can make an informed decision on how to adjust your image.
Many cameras now give you the option to view a histogram on the camera’s monitor – either live, while taking the picture, or afterwards. In either case, the in-camera histogram is non-editable and can only be adjusted by transferring the image to your PC and editing it in Photoshop or another image-editing program.
To open the Levels palette and view the image’s histogram, open your image and, from the Image Menu, select Window > Levels.
Even though your image is black and white, it can be useful to keep the colour space as RGB. This way you can view each colour channel as a separate tone, selecting individual channels from the drop-down menu and making selective tonal enhancements. Dragging the sliders underneath the histogram will alter the highlights (left) the midtones (middle) and the shadows (right). Follow the simple steps below to use the Levels palette effectively.
The Levels Palette Options
Click on the options button, and the Auto Colour Correction Options palette will appear:
These are automatic pre-set adjustments that alter the image globally, using specially designed algorithms. They can clip all channels identically, or maximise the tonal range in each channel to produce a more dramatic correction. Select Snap Neutral Midtones if you want Photoshop to average out the neutral colour.
1 Colour channel drop down menu
Use this drop down menu to select the histogram of each colour channel. Either Red Green or Blue, or even the composite.
2 Input levels
The boxes show the pixel value for maximum black, mid grey and white.
Use this as an illustration of your image’s highlights and shadows.
4 Shadow slider
Use this black slider to darken the image.
5 Midtone slider
Use this grey slider to alter the midtones.
6 Highlight slider
Use this white slider to lighten the image.
7 Output levels
Enter the figures manually to alter the global tones and reduce contrast.
8 Global tone
Drag these sliders to alter the brightness of the entire image.
9 Button options
Use these buttons to save adjustments or load in existing levels.
Use these pickers to select pure white, black and grey areas of the image.
Top Clips: When you move the left or right slider hold down the Alt key at the same time. The screen will go black (highlight) or white (shadow) and the shadow and highlight details that are being lost (or clipped) will show as spotted colours. Keep these to a minimum for full detail.