Some image editing habits become so ingrained that it is hard to unlearn them when newer ways come along and make the old favorite methods redundant. An example of this is the subject of setting the output Levels in Photoshop for the print output. For many years Photoshop users were taught to set the output levels for the shadows at a slightly higher value than 0,0,0, even though (as you will read here) it has not been necessary to do so for quite some years now. Then came along Camera Raw and Lightroom and some photographers have been agonizing over how to set the output levels for an image when there is no output levels control in Camera Raw or Lightroom. Hopefully the following article will help shed some light on how Photoshop is still able to manage the output levels for you and why the solution is really a lot simpler than you would think.
You will sometimes come across advice that the output levels for the black point in an RGB image should be set to something like 20, 20, 20 (for the Red, Green, Blue RGB values) The usual reason given for this is because anything darker than say, a 20, 20, 20 shadow value will reproduce in print as a solid black. Just to add to the confusion, some people may suggest different numbers for the output levels: someone may suggest using 10,10,10, while another advises you use 25,25,25. In all this you are probably left wondering how to set the Blacks in Camera Raw, since you can only use the Blacks slider to clip the Black input levels and are offered no means to set a black levels output value using of the above suggested output settings.
This is one of those areas where the advice given is more complex than it needs to be. It is well known that because of factors such as dot gain, it has always been necessary to make the blacks in a digital image slightly lighter than the blackest black (0,0,0,) before outputting it to print. As a result of this, in the early days of digital imaging, the only way to get a digital image to print correctly was to manually adjust the output levels so that the black clipping point matched the print device. Back then, if you set the levels to 0,0,0, RGB, the blacks would print too dark and lose detail in the shadows. The solution therefore was to set the Output levels point to a value higher than this (such as 20,20,20 RGB), so that the blacks in the image matched the blackest black for the print device. These are the background reasons for such advice, because the black levels had to be adjusted differently for each type of print output including CMYK prepress files.
For the last 10 years or so, Photoshop has had a built-in automated colour management system that is designed to take care of the black clipping at the print stage. The advice these days is therefore really quite simple: you decide where you want the blackest blacks to be in the picture and clip them to 0,0,0, RGB (as discussed on the previous page). When you save the image out to Photoshop as a pixel image and send the image data to the printer, the Photoshop or print driver software will automatically calculate the precise amount of black clipping adjustment that is required for each and every print/paper combination. In the Figure 3.xx example you can see how the black clipping points for different print papers are automatically compensated when converting the data from the edited image to the profile space for the printing paper. But don’t just take my word, it is easy to prove this for yourself. Open an image, set the Channel display in the Histogram panel to Luminosity and refresh the histogram to show the most up-to-date histogram view. Then go to the Edit menu, choose Convert to Profile, select a CMYK or RGB print space and compare the before and after histograms.
Figure 1. Here is the image that was used to generate the histogram panel views shown in the Figures below.
Figure 2. This Histogram panel view shows the original histogram for this ProPhoto RGB image. Note that this histogram and the others shown here all used the Luminosity mode since this channel view mode accurately portrays the composite luminance levels in each version of the image.
Figure 3. This histogram shows a comparison of the image histogram after converting the ProPhoto RGB data to a print profile space for Innova Fibraprint glossy paper printed to an Epson 4800 printer. The print output histogram is overlaid here in green and you can see that the black levels clipping point has been automatically indented.
Figure 4. This example shows the print profile for a Somerset Velvet matte paper printed to an Epson 9600 printer, again colored green so that you can compare it more easily with the before Histogram. The black clipping point is moved inwards even more here because the matte paper needs a higher black clipping point to avoid clogging up the shadow detail. The same thing also happens when you make a CMYK conversion, but the black point will possibly shift inwards even more.
So is it wrong to set levels manually?
Not really. All l I am suggesting here is that it is an unnecessary extra step to use Photoshop to set the black output levels to anything higher than the zero black after you have already set the black clipping to the desired setting at the Camera Raw editing stage (or done so in Photoshop). If you do set the black output levels manually to a setting that is higher than zero you won’t necessarily get inferior print outputs, providing that is, you set the black levels accurately and don’t set them any higher than is needed. And there’s the rub: how do you know how much to set the output levels, and what if you want to output a photo to more than one type of print paper? You see, it’s easier to let Photoshop work this out for you.
Some picture libraries are quite specific about how you set the output levels, but their suggested settings are usually very conservative and unlikely to result in weak shadows when printed to most devices. It is therefore probably better to oblige the libraries with what they ask for rather than fight them over the logic of their arguments.
The only time when you may need to give special consideration to setting the shadows to anything other than zero, is when you are required to edit an already converted CMYK or grayscale file that is destined to go to a printing press, where the black output levels have been incorrectly set. But as I say, if you use Photoshop color management properly you won’t likely encounter such problems.
In conclusion I would say that you shouldn’t need to worry about what the output levels should be. If you are editing a photo in Camera Raw or Lightroom, all you need to concern yourself with is applying the black point clipping that you feel is most appropriate for each individual image. Then let Photoshop or Lightroom take care of the black point output levels conversion at the point where you send the image data to the printer.
About Martin Evening
Martin Evening is the author of Adobe Photoshop CS3 for Photographers as well as the Adobe Photoshop Lightroom Book. Martin is a London based fashion and beauty photographer as well as an alpha 7 beta tester for Adobe. He is also a founding member of Pixel Genius and was the product manager for PhotoKit Color 2.