Two common types of synthetic images created in Photoshop are gradients and step wedges. The most common gradient is an even field, from black to white, to test for the smoothness of your display or print. The most common step wedge set is a set of patches from black to white in a specific number of steps, created from the type of gradient described above.
Color Management has required building synthetic images of these types in Photoshop since time immemorial. This gives us the long memory to recall the changes that have occurred over time, with updated versions of Photoshop.
The first of these changes, which happened along about Photoshop 6 (not CS6) was a change to the algorithm used to define gradients. The Photoshop team felt their linear gradients did not look as smooth as they could, so a S-shaped spline curve was introduced into the process. This did, indeed, improve the visual look of gradients, but it was problematic for technical uses, where a linear gradient was needed. So complaints were lodged, and an update included a checkbox for restoring the earlier, more linear, behavior, where the gradient darkened by the same amount for each unit of distance, rather than feathering at the ends.
More recent versions of Photoshop have added a slider control for adjusting this function. It can be found in the Gradient Editor (which appears when you choose the Gradient tool, then click on the gradient itself in the bar at the top). This slider is named “Smoothness”, and its default setting is 100%. This means “100% smoothed” and is the inverse of “100% linear”; so the Smoothness slider is set to zero to get a linear gradient.
A visual comparison of a smoothed gradient, and a linear gradient, is the best way to understand the difference between the two.
This may be of value to those wanting to create test images, and know that one inch across is half as much change as two inches across, but there is another, more practical reason that knowing how to create a linear gradient: such gradients are the basis for creating step wedges as well.
A step wedge is a set of patches, typically squares, with known values, typically running from white to black in 10, or 20, or sometimes 256 steps. Such patches can be measured on screen with a screen colorimeter such as a Spyder, or in print with a patch reader such as SpyderPrint.
Gradients are turned into step wedges by using Photoshop’s Posterize function (Image > Adjustments > Posterize), with the appropriate number of levels selected.
If a gradient is created at Photoshop’s default smoothness setting, the result will be a set of steps which have longer patches at the ends, and shorter patches near the center, due to the smoothing curve. This can cause a great deal of frustration to someone attempting to build a strip or table of patches with both even sizes, and known values.
So the magic control for creating evenly spaced step wedges or target patches is the Smoothness control, hiding in the Gradient Editor. Another key to a good set of step wedges is turning off the Dither option in the Gradient bar, to avoid step wedges with grainy edges, from the dithering applied to the gradient when it was created. To assure gradient edges are vertical, and not stepped a pixel here or there, hold down the shift key while dragging to draw the gradient, to be sure it is exactly straight. And a final tip (thanks to Ernst Dinkla for mentioning this one) has to do with mathematical precision in your patches: choose 16 bit mode, and 16 bit units, if your number of patches does not divide evenly into your scale of 100 or 255. Keep these tricks in mind, next time you would like an even set of patches; for technical, or just for graphic design, purposes.