Setting tone values and correcting colors

Preparing images for printing


You are getting images ready to print in one of your famous publications. You get some that are good, bad, and...ugly. You would like them to look good or thereabouts when they print.

This issue includes some historical photos that will need some work.


The exercise:

A basic Photoshop 8-bit image has RGB or CMYK channels with 256 levels of information for each pixel in each color channel.
The magical color correction tools do their work by applying some math to every pixel to raise of lower its value.

The Curves tool shows the most straightforward picture of what is going on within your images. Levels has less detail, but is pretty clear. The other ones with tricky names like Brightness are built to do the job of the Curves with an automatic interface. They can accomplish the job, but if you understand Curves you will also understand why the magical effects are happening.

What to do

You will be using Adjustment layers to correct images. You can do everything on one adjustment layer but it is more confusing. The effects of all the adjustments add together in the end so it is fine to make a layer for each task. It will be more understandable now, and if you open the file far in the future and need to make changes.

Repair these files:

Use separate Levels adjustment layers to:

A. Adjust the tonal range of each color channel (RGB) to maximum light and dark values. Use the Option key while sliding the controls to judge where the information appears.

B. Set the output levels to provide a highlight and shadow value for the print shop. Use the typical setting of 5% highlights (13) and 95% shadows (242).

C. Adjust for color balance by setting a color sampler(s) in some image areas you believe are neutral colors, such as white objects, gray concrete, etc. Make the sample size 3x3 or 5x5 to get a better average reading.

Levels are the easiest to understand with their four end point sliders and a midpoint. You can also do all these operations with Curves. Curves gives you control over the entire tone range, but it takes more practice to control it. What you can do with Curves, and not Levels, is make an “S” curve. An “S” curve adds a little boost, the “toe”, to the extreme light and dark ends of the tone range. It makes the light tones brighter and the dark tones darker, without clipping the details in those areas. It is the real story behind using an automatic contrast adjustment.

D. Also try a Curves adjustment layer with a slight "S" curve to improve the contrast, or, as they say, "make it pop!".

Turn them in to the Corrected Colors folder in dropoff.