Printer White Point

Determine where a printer stops printing detail in the highlight areas and resorts to 'printing' solid white

 

The lower the black point value and the higher the white point value, the broader the tonal range your printing environment can reproduce.

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Be sure to read the Printer Black Point section first since it contains useful background information.

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Step One - Determine Printer White Point

Simply put, the white point is the point where the printer no longer lays down any ink and lets the white of the paper represent white.  A printer's white point needs to be determined for every combination of paper, ink, printer, print engine and printer profile you use.  To keep track of your various white points, you can print and use the Printer Chart to record your white point values.

The specific steps to determine the white point are listed here.

1. Download the printer white point target from the Downloads page.  The download version will not have the word Sample printed across it.
2. Do not apply any Photoshop adjustments to this file.
3. Using the same process you use to print your images, print the target for every combination of paper, ink, printer, print engine and printer profile you use.  If you use Photoshop, instead of a RIP, to print your images, you may wish to review the Photoshop Printing page.
4. Let the target dry for at least 15 minutes.  A day or two would be better to allow the ink to cure and the solvents to dissipate.
5. Using a strong light source, such as direct sunlight, look at the bottom two rows.  Looking at the target at an angle may help.
6. The bottom two rows skip every other tone to make it easier to narrow in on the white point.  What you are looking for is the lightest tone that is distinguishable from its darker tone neighbor but is indistinguishable from (blends in with) all of its lighter tone neighbors.  The higher the number, the lighter the tone.
7. Once you think you have found the white point, find this same tone in the first three rows.  The first three rows show tone in increments of one.  Fine tune which tone is the white point.
8. Record this value on your Printer Chart.

 

What are we looking for

Lets use Figure 2 to better understand what we are looking for.  Figure 2 shows four tones: A, B, C and D.  Tone D is easily distinguishable from tone C.  Tone C is easily distinguishable from tones B and D.  Tone B is distinguishable from C but not A.  Therefore, given the definition that a printer's white point is the lightest tone that is distinguishable from its darker tone neighbor but is indistinguishable from (blends in with) all of its lighter tone neighbors, then tone B is our white point.  This is the tone where the printing environment stops distinguishing between light tones and resorts to not laying down ink.

 

 

Step Two - Set An Image's White Point

You only have to find the white point once for every combination of printer, paper and ink.  However, you have to apply a white point adjustment to every image that has highlight detail you want printed.  There are two methods for doing this.
 

Customary Method

The customary method uses the Levels adjustment.

• Create a Levels adjustment layer by clicking Layer > New Adjustment Layer > Levels.  Or, by clicking the Create adjustment layer icon at the bottom of the Layers palette.
• Change the Output Levels white value, 255, to the desired white point value.
• Click OK
• Change the adjustment layer's blending mode to Luminosity.

Once you make your adjustment, you will probably see a slight overall darkening of the image.  This is the tradeoff we give up in order to print the details in the highlights.  How much darkening appears depends on the white point value.  If the white point value is 250, there will be very little.  If the white point is 220, then you could see darkening past mid tone.

 

 

The Curves Method

The adjustment I prefer to use in setting the black and white points is a Curves adjustment.

Create a Curves adjustment layer.

1. Click Layer > New Adjustment Layer > Curves.  Or, by clicking the Create adjustment layer icon at the bottom of the Layers palette.
2. Ctrl + Tab (Command + Tab) until tone 255 is highlighted.  It is highlighted when the small circle in the upper right corner becomes solid black.  Tone 255 has a red circle around it in Figure 4.
3. When properly highlighted, the Input and Output boxes will be displayed, both will have the value 255.
4. Change the Output value to the white point value.
5. Click OK.
6. Change the blending mode to Luminosity to prevent any possible affect on the image's color.
7. Using black paint, paint in the layer mask so the texture-less highlight areas will not be darkened.

 

Apply both Black and White Points

Just like the Levels control, we can use a single Curves control to apply both the black and white point adjustments.

1. Download the Curves adjustment from the Downloads page.
2. Create a Curves adjustment layer.
3. With the Curves dialog box open, click the Load button.
4. Locate the downloaded file and click Load.  The curve should look like Figure 5.
5. Ctrl + Tab (Command + Tab) until the tone 0 marker is highlighted.  It is circled in black in Figure 5.
6. Type the black point value in the Output box.
7. Ctrl + Tab (Command + Tab) until the tone 255 marker is highlighted.  It is circled in white in Figure 5.
8. Type the white point value in the Output box.
9. Click the Save button. 
10. Name the file so that it represents the printer-paper-ink combination the adjustment is for.
11. Click Save.
12. Click OK to close the Curves dialog box and apply the adjustment.
13. Using black paint, paint in the layer mask so the texture-less dark and highlight areas will not be affected.

 

By saving this adjustment, you can reuse it for future images that are to be printed using the same printer-paper-ink combination.