DickN wrote:I infer from your question that you suspect a display rendering artifact.
Yes I think it may have been.
I agree that it can look quite odd, and while I understand that running the Nyquist effect will cause a redraw I don't know why the redraw should be any different from one time to another. In the situation when I first noticed it, I checked to see if there was any change in the data outside of the selected region. There wasn't.
DickN wrote:Why does the forum s/w reject pdf's?
Believe it or not, I think you're the first person to ask about PDF upload
For uploading pictures I'd recommend either PNG or JPG format. Most screenshot tools support one (or both) of these file types and all of the main web browsers support them so that they can be inserted as images. A PDF file would not display and would have to be downloaded by the user to view it with their PDF viewer (which may or may not be integrated into their web browser).
GIF images are good for diagrams, or pictures that have very few different colours. Gif is also supported natively by most web browsers.