Histogram histrionics

For some time I have been plagued and annoyed by some unusual effects in histograms of my photos. The histograms just did not seem right, nor was there consistency on how they displayed in different post-processing apps.

To shed some light on what I was experiencing I prepared a special image. All the pixels have identical values for the red, green, and blue channels. There are pixels for all possible values, from 0,0,0 to 255,255,255. In fact, the image contains about 11,200 pixels of each value (more for pure white, an extra row). The image format is PNG so there is no compression. Yes, it took me a while to prepare the image. It is “just a gray wedge” you might say.

What should the histogram for this image look like? Well, all values are represented, and each has the same number of pixels, so it should be a straight horizontal line, or a plain rectangle. Indeed, when the test image is loaded into PaintShop Pro 2022 it looks just like you’d expect:

Here comes the “amuse”:

This image does not provide the same uniform histogram in ON1 Photo RAW 2022. Let’s look at the histogram there a little closer:

Strange? It gets stranger still.

As I mentioned, the image is in PNG format. I loaded it into ON1 Photo RAW 2022 and exported it as a best quality JPG image. It looked the same to the eye as the original. When loaded into PaintShop Pro 2022 the histogram was not the uniform rectangle as the original but looked like this:

In the middle region the histogram looks like what is expected. The black end and white end, however, are strange.

It is those same strange “end-effects” that I have seen in photos processed in ON1 and exported as JPGs.

We’re not done with the situation; it gets stranger still more.

Loading the ON1-export into NX Studio gives me this:

Here the histogram does not show the “end-effects”. The histogram, although not neat and uniform, is pretty close to what is expected.

So, dear reader, that brings me to the end of my histrionics. I don’t know what to make of it. Go ahead, admire my work of art:

.:. © 2022 Ludwig Keck