Setting Black & White Points
using Photoshop Levels adjustment

Before I launch into the 'how to' part of this article, lets spend a moment understanding why "setting the black & white points" is so important to good quality output.

It's all boils down to Dynamic Range. In terms of printing, dynamic range is the scale of difference between the darkest printable black and the lightest printable white. The greater the dynamic range the more available contrast there is. An image that is printed using the full dynamic range (maximum available contrast) of a printing process is going to look much more punchy than one that does not. Notice in the example below the murky whites and washed out colours of Image 1 compared to the punch and contrast of Image 2.

Image 2
More punchy as it fully utilises available dynamic range.
Image 1
Not fully utilising the available dynamic range

By setting the darkest black in our image to the darkest black of the printing process and our lightest white to the lightest printable white we are ensuring that the image will use as much of the available dynamic range as possible. This process is known as 'setting the black and white points'.

Photoshop Levels

For this tutorial I am going to use CS2 but there is little difference between all the CS versions.

Levels Adjustment LayerOpen up an image in Photoshop (feel free to download my sample image).

From the menu select Window Layer to open up the Layers Window.

Click the button at the bottom of the window that looks like a half black and half white circle. A menu will appear. Select Levels.

You have just created a Levels Adjustment Layer, which you can see in the Layers Window.

You will also see that the Levels dialogue box has appeared, with a histogram (bar chart representing the tones in the image) and 3 sliders immediately beneath it.

Make sure that the Preview check box is checked and have a play with the Black slider on the left. Notice as you slide it inwards that the image darkens. Now do the same with the White slider and notice how the image lightens.

Slide the Black slider until the number 75 appears in the leftmost Input Levels box. Notice how almost all the detail in the ground floor car park is lost. This is called Clipping because you are telling Photoshop to treat all tone levels from 0 to 75 as if they are pitch black, thereby clipping out detail.

If you now press the ALT key on your keyboard you will notice that the Cancel button in the Levels dialogue box turns into a reset button. Click the reset button.

Accurately setting the Black & White points

Few people seem to know about a very useful feature of the levels dialogue box, which is the Clipping View.

While holding down the ALT key Click&Hold the mouse down on the Black slider. You image will turn white. Gently slide the Black slider to the right until some coloured pixels start to appear. These are the first pixels that will be clipped if you continue to move the slider. Ease the slider back until the pixels have just returned to white. This is the perfect spot to set the Black point. If you have used my sample file the Black slider should be set to 15.

Now repeat this process for the White slider. Pressing the ALT key as you slide will turn the image black and again coloured pixels will appear as a clipping warning. If you have used my sample file the White slider should be set to 225.

You have now correctly set the black and white points for your image.

Click the OK button which will save your adjustments into the adjustment layer. You can review the effect of the newly created Levels adjustment layer by turning it on and off in the Layers Window (Click the 'eye' icon to the side of the layer).