Malte wrote:

Hi all,

I recently did a little test in Photoshop and came up with two strange observations. Here is the experiment:

- Create a new image being 256 (or an integer multiple of this) wide and, say, 100 pixels high.
- Specify white to be the foreground and black to be the background color (press D).
- Draw an exact horizontal linear gradient from the very left to the very right of the image, or vice versa (hold SHIFT to ensure it is horizontal).

Here are the observations:
- Use the eyedropper tool to browse over the image and look at the info palette. There are some pixels that have non-neutral color values (i.e. the values for red, green and blue differ by 1). Why is that? A gray-scale gradient should only contain neutral colors, shouldn't it?

Sure should. I haven't found a way around this. It appears to be a one bit +- dither, but with vertical stripes that run perpendicular to the gradient.

- Have a look at the histogram (either use the Levels dialog or select Image/Histogram from the menu). The shadows and highlight are higher than the midtones. Why is that? A gray-scale gradient should have an exact flat histogram, shouldn't it?

You and I think so, but try to realize - heh - that a spline is a much more natural way to start and stop a gradient. In the bad old days of PS 5.0, this was not optional. Luckily as of 6.0 you may disable this "feature" by editing the gradient, and cranking the smoothness down to zero.

I tried to do this experiment in different color spaces, such as Adobe RGB (1998) and sRGB. The results are always the same. BTW, I used Photoshop 7 but I suppose the result is not much different in Photoshop CS, is it? Does anyone have a nice explanation for this?

The explanation is that vitamin and hormonal additives found their way into the gradient tool after version 4.0. Thank God, or another power with a three letter name, that we at least have the smoothness adjustment.

Best regards,
Malte.

malte.stien

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Non-neutral colors in gray-scale gradient in Photoshop. Why?