Why did these pixels move?

[Patrick Cooper]

Fairly recently, I was working on a project with Bezier curves. I drew a curvey line, filled it with black and then drew a circle and filled that with yellow and deleted the paths of both elements. You can see a zoomed in crop of the right part of the image here.

 

 

Later on, I filled the white background with orange. Then after that, I dragged another object on to the image. However, zooming into the completed image, it looks like the pixels in that wavy line have shifted. By coincidence, they have shifted at the point where the circle meets the line.

 

 

And a similar thing has also occurred on the left side of the image (at the point where the other side of the circle meets the wavy line) What could be causing this? And how do I prevent it from happening again? I was working with Tiff files by the way. Saving different versions as Tiffs as I made different changes.

And just now, I did a test. With the first file, I filled in the white background with orange temporarily and the pixels in the line remained the same.

 

I did absolutely nothing to that diagonal line. The pixels shifted by themselves. So I'm wondering what caused this. With the second file on display, I did three things. 

1. I filled the background colour with orange.

2. I cropped the image below the diagonal line.

3. I dragged an element from another image on to this image and moved it around and rescaled it. I positioned it above the diagonal line.

So would any of these things have likely caused the pixels to move? I'm using Photoshop CS4 by the way. I admit this is really bizarre and Ive never experienced anything like this before.

[Michael Ventura]

These are 1200% and 800% crops, you will get stair stepping in pixels at that magnification.  Maybe I am not understanding what the issue is.

[Patrick Cooper]

Yes not surprisingly, there is stair stepping at those magnifications. Though it's also clear in the second image that some of the pixels in that diagonal line have moved. They are in a different position compared to the first image. After the point where the circle intersects with the line, the pixels are lower (on the right side of the image.) 

[Patrick Cooper]

I actually wonder if the pixels have really moved or if it's a display issue. Then again, if it's a display issue, why is it only viewable in later versions of the image and not in the first version? It is indeed a mystery.

[Patrick Cooper]

Actually, Ive just had another look at 33% and 50% zoom with reading glasses on and I can just make out a slight bump on the line on each side of the circle with the line a fraction lower on the left and right. It is extremely slight. So I doubt it's a display issue.

 

Hmmm....I suppose one solution could be to simply select and cut out the good segments from the earlier version (where the wavy line is consistent) and drag them on to the later version and carefully align them. Like a basic path up job (covering over the inconsistent bits.)

Edited November 29, 2019 by Patrick Cooper

[Patrick Cooper]

My patch up job worked. I dragged the 'good' sections from the old version to the new version, aligned them carefully in place and then merged the layers. It looks pretty seamless now (when zoomed in or out.)