Printer Black Point

Determine where a printer stops printing detail in the shadow areas and resorts to printing solid black

 

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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If you are unfamiliar with the Photoshop Levels and Curves controls, it is suggested you read the Levels section and the Curves section before continuing.

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The ability of monitors to display detail in shadow areas is usually better than a printer's ability to reproduce them.  Therefore, there is the possibility of seeing detail on a monitor that, when printed, prints as a solid black or a very dark gray.

Lets assume Figure 1A represents the tones found in an image.  Tone A is the darkest tone, B is the next darkest, then C and then D.  As shown in Figure 1A, Photoshop (and a good monitor) can distinguish between the four tones.  However, a printer is not as fortunate.  Many printers have a difficult time reproducing subtle differences in the darker tones.  Figure 1B represents how the same image might be printed by a printer.  As we can see, tones A and B blend together.  We cannot tell where one begins and the other ends.

Figure 1A.  What Photoshop sees

Figure 1B.  What your printer sees

The tone at which the printer can no longer distinguish between it and the next darker tone is known as the black point.  For critical printing, it is important to know where this transition is so we can bring the detail up into the tonal areas the printer can handle.  To accomplish this requires two steps.

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The Two Steps

Step one is to determine where the printer no longer prints discreet dark tones.  This step is not performed for every image.  It needs to be done only once for every combination of paper, ink, printer, print engine and printer profile you use.  The second step is to manipulate the image's tonal range so shadow detail will print.  The second step has to be done for every image that has shadow detail you want printed.  This topic covers both steps.

 

The ability of a printer to print detail in the shadow areas of an image is dependent on more than the mechanical components of the printer.  It is also dependent on the ink being used, the paper being printed on, the software (print engine) used to do the printing and the device profile used by the print engine (not the profile embedded in the image).  For more on device and image profiles, you may wish to read the Profiles page.

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Step One - Determine Printer Black Point

A printer's black 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 black points, you can print and use the Printer Chart to record your black point values.

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

1. Download the printer black 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 black point.  What you are looking for is the darkest tone that is distinguishable from its lighter tone neighbor but is indistinguishable from (blends in with) all of its darker tone neighbors.  The lower the number, the darker the tone.
7. Once you think you have found the black 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 black point.
8. Record this value on your Printer Chart.

 

What are we looking for

Lets use Figure 3 to better understand what we are looking for.  Figure 3 shows four tones: A, B, C and D.  Tone D is easily distinguishable from tone C.  Tone C is easily distinguishable from tone B.  Tone B is distinguishable from C but not A.  Therefore, given the definition that a printer's black point is the darkest tone that is distinguishable from its lighter tone neighbor but is indistinguishable from (blends in with) all of its darker tone neighbors, then tone B is our black point.  This is the tone where the printing environment stops distinguishing between dark tones and resorts to printing solid black.

 

 

 

Step Two - Set An Image's Black Point

You only have to find the black point once for every combination of printer, paper and ink.  However, you have to apply a black point adjustment to every image that has shadow 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.  Figure 4 shows a Levels dialog box.  We need to change it so our darker tones are remapped based on the black point value we determined above.  However, I am not going to tell you how to do this (at least, not at first).  You are going to tell me.

I will give you a couple of hints first.

• The value that needs to be changed is either the Input Levels value highlighted in red or the Output Levels value highlighted in red.
• Input Levels is used to remap what tone in an image is solid black (tone 0).  If changed to, for example, 21, then Photoshop will remap the darker tones so tone 21 becomes solid black.  Output Levels is used to remap what tone in an image is the darkest tone allowable in the image.  If changed to 21, then tone 21 becomes the darkest tone allowed in the image and Photoshop will remap the darker tones so no pixel is darker than 21.

 

So, which value do you think we need to change?  The Input Levels value or the Output Levels value?  Once you think you have the answer, click below to see if you are correct.
 

1. My answer is to change Input Levels
   1. Sorry.  In images with shadow detail we want printed, we need to tell Phtoshop the black point is the darkest tone in our image.  This is not the same as telling Photoshop to remap our black point to solid black.  If we used Input Levels, we would actually compound our problem by moving shadow detail into even darker tones.  What we need to do is move shadow detail into the lighter tones the printer can reproduce.  You may wish to review the Levels Output page.
2. My answer is to reset Output Levels
   1. Yes!  You are correct.  By typing the black point value as the Output Level, you are shifting shadow details into lighter tones the printer can handle.

 

 

Once you make your adjustment, you will probably see a slight overall lightening of the image.  This is the tradeoff we give up in order to print the details in the darker shadows.  How much lightening appears depends on the black point value.  If the black point value is 5, there will be very little.  If the black point is 30, then you could see lightening all the way into Zone VIII.  This is why I prefer the Curves Method instead of the Levels method when my black point adjustment causes a major shift in contrast.  Remember, we are only trying to shift the dark details into tones the printer can handle, not change the overall contrast of the image.

 

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 by clicking Layer > New Adjustment Layer > Curves.  Or, by clicking the Create adjustment layer icon at the bottom of the Layers palette.  Figure 5 shows a Curves dialog box.  We need to change it so our darker tones are remapped based on the black point value.

1. Ctrl + Tab (Command + Tab) until tone 0 is highlighted.  It is highlighted when the small circle in the lower left corner becomes solid black.  Tone 0 has a red circle around it in Figure 5.
2. When properly highlighted, the Input and Output boxes will be displayed, both will have the value 0.
3. Change the Output value to the black point value.
4. Click OK.
5. Change the blending mode to Luminosity to prevent any possible affect on the image's color.

 

Non-Linear adjustment

Since Levels and Curves are non-linear controls (a change in dark tones will gradually taper off to where the lighter tones are not affected), the closer a tone is to the black point the more it will be affected.  Even though this is exactly what we want in order to bring shadow detail up into lighter tones the printer can handle, if the black point value is large enough, then a fair amount of the image could be affected.

Figure 6 shows an adjustment for a black point of 34.  (Yes, I actually do have a 100% rag, matte paper whose black point is 34.)  The red line shows the default curve, the black line shows the adjusted curve and the green area shows how much each tone is being changed.  As you can tell, the affect tapers off the closer you get to white (upper right corner).  However, the affect goes well into the middle tones and beyond.

How do we isolate our black point adjustment to just the areas we want?  This is where anchor points on the Curves control come in.  And this is the very reason why I like to use Curves to make this adjustment.

Figure 7 shows the same adjustment, but with anchor points.  As you can tell, even with a large black point, only Zones O through II are being affected while Zones III through X are unaffected.

You can add the anchor points yourself, or you can download a Curves black/white point adjustment, with locking anchors already in place, on the Downloads page.
 

Dark, Texture-less tones

I often find when I apply the black point adjustment, using either Levels or Curves, certain dark tones with no detail become lighter than I would like and they lose their richness.  The solution to this is a layer mask.  If you used an adjustment layer to apply the Levels or Curves black point adjustment, activate the layer mask by clicking on the layer mask thumbnail in the Layers palette.  See Figure 8.  Then type the letter d to set the default foreground colors to black and white.  If black is not the foreground color , type the letter x once.  Then use an appropriately sized brush to paint in the layer mask (not on the image) to block these tones from being affected by the adjustment.  Areas painted black will not be adjusted.  Areas left white will be adjusted.

 

 

Unusually High Black Point Values

Since a black point is dependent on the combination of paper, ink, printer, print engine and printer profile, there are no hard and fast black point values.  (If there were, we would not have to find our own black point values.)  However, you may encounter a situation where the black point value seems too high.  Using Epson printers as a guide, generally you can expect black points for glossy and luster papers to be in the single digits to the mid teens.  For matte papers, it may go all the way into the low 30s.  If you get unusually high black point values, you may wish to check the following.  They are in order of most likely to be the cause, to the least likely.

• Are you using an ICC profile in your printing steps?  If you are using Photoshop, and not a RIP, to print your images, review the Photoshop Printing page to be sure you are following the proper steps to print your image.
• Are you using a custom ICC profile for the specific paper and ink being used (and not a generic profile)?
• Are you using quality paper and the printer manufacturers ink cartridges?
• Does the printer pass the head alignment and nozzle checks?
• Are your ink cartridges out of date?
• Are you reading the printed target correctly?  The difference you are looking for is very, very subtle and will be hard to spot (unless you have jet fighter pilot eye sight).  If the black point value you are deciding upon has an obvious difference to its lighter toned neighbor, then you need to look more closely.
• Get a second opinion.  Someone with better eyesight might find a lower black point.
• Very unlikely, but possible, there could be something wrong with the printer.  If you can get a low black point using glossy paper, then it is not the printer.

 

Summary

By using a Curves adjustment layer with anchor points and a layer mask, we can print our shadow detail, and dark tones with no detail can remain unchanged in order to retain their deep, rich color.

 

FAQ

Question.  I have an image whose tone is fairly evenly distributed from dark to light and when I apply the black point compensation to my image, the overall image gets lighter.

Answer.  This usually happens when the black point adjustment is a high number and the adjustment is made via Levels or a straight line Curves adjustment.  Apply your adjustment using a Curves adjustment layer utilizing anchor points that lock the mid tone and highlight areas in place.  What we are trying to do is bring those dark areas with detail into the range the printer can handle.  There is no need to shift the mid tone or highlight areas.  However, if Levels or a straight line Curve is used, more than the dark areas will be affected.
 

 

Question.  I applied a black point adjustment to my image, but the dark areas just became a muddy gray.  I liked it better without the adjustment.

Answer.  When you apply a black point adjustment, we are shifting dark areas into lighter tones so the printer can reproduce the detail in the dark areas.  If there is no detail, then the dark areas will become lighter and not look as rich.  I always apply my black point adjustment using a Curves adjustment layer with a layer mask.  At first, the layer mask is solid white.  Once I apply the adjustment, I zoom in on the dark areas.  For those dark areas without detail, I paint in the layer mask using black paint.  This blocks the adjustment from this area.  Be sure you paint in the layer mask and not on the image itself.  (Sometimes this is easily missed since we are masking dark areas.).  Please read the section Dark, Texture-Less Tones above.