Quick Start Instructions for Levels

More detailed instructions are given below

Auto Levels

1. Open your image file in Photoshop.
2. Perform Auto Levels
   
   • Photoshop CS2: Image > Adjustments > Auto Levels
   • Photoshop Elements: Enhance > Auto Levels

Levels

1. Open your image file
2. Perform Levels
   
   • Photoshop CS2: Image > Adjustments > Levels
   • Photoshop Elements: Enhance > Adjust Lighting > Levels

Reset

Alt+click on Cancel to undo Levels changes (on the Levels dialog box).

Detailed Levels Tutorial

Auto Levels

Sometimes correcting contrast is as simple as using Auto Levels. To apply Auto Levels to an image:

Step 1

• Open image

Here is an example and its histogram. You can see an informational histogram in Photoshop CS2 by clicking on the menu item Windows and then choosing Histogram in the drop down menu, or in Photoshop Elements by selecting Image and then Histogram in the drop down.

Original

Histogram of Original Image

Step 2

• Apply Auto Levels
  
  • Photoshop CS2: Image > Adjustments > Auto Levels
  • Photoshop Elements: Enhance > Auto Levels

Examine the image and the Histogram. Here they are after Auto Levels has been applied:

Image after Auto Levels

Histogram of Image after Auto Levels

Step 3:

If unsatisfied with the results "Undo" and go to the Levels discussion immediately below.

To undo in Photoshop or Photoshop Elements: Edit > Undo [PC Keyboard shortcut is Ctrl-Z]

Levels

Frequently, Auto Levels does not produce satisfactory results. In the discussions below, one generally uses either Adjust Input and Output Levels or Setting the Highlight and Shadow Values (see below).

Adjust Input and Output Levels

Step 1

• Open image.
• Open Levels Dialog Box (to display histogram).
  
  • Photoshop CS2: Image > Adjustments > Levels
  • Photoshop Elements: Enhance > Adjust Lighting > Levels

Original Image

Histogram for Original Image

Step 2

• Examine histogram - it illustrates how pixels are distributed by graphing the number of pixels at each color intensity level. This area under the curve shows if there is enough detail in shadows (left side of the histogram), in mid-tones (the middle of the histogram), andin highlights (right side) to make a good correction.
• Adjust Input levels - the top portion of the Levels dialog box includes the Input Levels numbers and three sliders. The Input Shadow slider, on the left, darkens shadows as you move it to the right. The Input Highlight slider, on the right, lightens highlights as you move it to the left. The Brightness slider, in the middle, adjusts the brightness of the image. Move the left and right sliders (e.g. the left first, then the right) until the slider is just below where the curve rise just touches the bottom of the histogram.

In this example the histogram is bunched against the left side, so the image is very dark. Move right slider to the left as indicated below.

Histogram showing right slider moved left

Resulting Image
(more detail visible in shadow areas)

Above the histogram (in the Input Levels boxes), the lowest and highest values of readings are inserted in the first and third (last) boxes for the composite RGB channel.

The middle number is for gamma adjustment which may further improve the image. You may need to bump gamma to 1.2 or 1.4, which would lighten the image, or in some cases reduce gamma, e.g. to 0.8, which would darken it.

Here is the histogram that results after moving the slider above (you have to open the Levels dialog box again to see it this way):

Step 3

Adjust Output controls - found on the bottom of the Levels dialog is the Output Levels numbers and two sliders. The Output Shadow slider (left) makes shadows lighter as you move it to the right. The Output Highlight slider (right) makes highlights darker or duller as you move it to the left.

Here's the result of moving the Output Shadows slider:

Note: this procedure can be used with the histogram showing RGB or RED, GREEN, or BLUE channels. On occasions, it is best to work with individual channels.

Advanced Usage of Levels

This section is an advanced usage of Levels - please ignore this section until you have mastered the steps above, applying the technique to several images.

Setting the Highlight and Shadow Values

Start with the same image as in the last example. Again note that the histogram is bunched up on the left side, indicating the image is very dark.

Original Image

Histogram for Original Image

Sometimes the only levels correction needed is to set to darkest and lightest points in the picture.

In the dialog box containing the histogram, double click on the leftmost (dark) eye dropper (lower right of the dialog box).

A color selection dialog appears. Set L=4, a=0, b=0 and click OK. This is the Color Picker that appears from the image above. Note the value for L=4, a=0, and b=0 as indicated:

Select the part of the photo that we believe to be the darkest section in the final image, e.g. Shadows.

This is the Color Picker that appears. Note the value for L=96, a=0, and b=0 as indicated:

This is the histogram and the image that resulted from clicking on what was thought to be the darkest point in the image:

Now double click on the light eye dropper.

A color selection dialog appears. Set L=96, a=0, b=0 and click OK.

Select the part of an image that we want to be the lightest portion in the image, e.g. white clouds in sky, hi-light on guardrail, white line on highway.

The resulting histogram has gaps in it, but it is spread out nicely. After the last action the histogram that resulted is shown. The final image from the dark and light eyedropper manipulations is also shown:

Reset

In case you make a mistake before leaving levels, you will need to know how to perform a reset:
Alt-click on the Cancel button - holding down "alt" will change the word in the dialog box from "Cancel" to "Reset", click (left mouse button) on Reset before releasing alt.

Levels have also been used to attempt correction for white balance problems with JPEG images - sometimes using the procedure "Adjust Input and Output Levels" to correct the Blue channel, and sometimes by using the eyedropper tool to select the lightest portion (original could have been blue because of white balance problems.)

As the result of applying levels, we now have images which look somewhat better, but they could possibly still be improved. We recommend that you continue your education utilizing other lessons in this series to:

• increase/decrease brightness
• alter hue/saturation
• crop, etc.