Purple areas appear when importing greyscale height map to Wilbur

[Koos98]

Hi! I'm new to this forum and only found out about the existence of Wilbur yesterday, when I saw some posts about it. Being able to make realistic rivers and erosion features just by clicking some buttons sounds great, but I'm finding that Wilbur has a pretty steep learning curve and I'm having trouble using it with an existing height map. It's a rough greyscale that I made a while ago. I figured I'd import it to Wilbur and play around for a bit, but when I imported it purple areas appeared on some mountain ranges. It looks like they're abruptly lowered and flattened somehow, and I have no idea why because I don't see any abrupt changes in those areas on the greyscale and they should be mountain tops, not depressions. They also show up on the bump shader texture as solid black and on the slope shader as black outlines. I've tried adjusting the greyscale image in a couple of ways in GIMP and importing it again but have mostly only succeeded in making things worse. If anyone knows what could be causing this problem (and how to solve it) I'd love to hear, because it has me stumped

Original greyscale:
Gimp.PNG

Purple areas:
Wilbur purple.PNG

Bump shader:
Wilbur bump.PNG

[waldronate]

I can't get the posted PNG (looks to be a grayscale 8-bit PNG) to do what you're showing with version 1.89 when using File>>Open to open it as either a grayscale image surface or a png surface.

What's happening is that the the purple stuff is where the sign bit (the highest order bit) changes from 0 to 1, meaning that Wilbur interprets it as negative values. Move your mouse cursor over the transition and watch the status bar in the lower-right to see the altitude change sign as the mouse across the transition. Note that Wilbur should never try interpreting PNG images as signed pixels, though, so I'm not sure what's happening.

How to fix this depends on how you're importing the data (that is, how you're saving it from The GIMP). If you're importing it as a raw binary raster, uncheck the "Signed" checkbox during the import. If you're importing it as some sort of image, do the following steps after reading the image:

1) Select>>From Terrain>>Height Range With How=Between, Operation=Replace, Minimum=-100000, and Maximum=-0.000001 to select everything too low.
2) Filter>>Mathematical>>Offset with an Offset of 32768 (if it's a 16-bit image) or 256 (if it's an 8-bit image) to lift everything up to the baseline height.

[Koos98]

Thank you so much for the quick and detailed reply! I don't have access to my personal computer atm but I will try your solution as soon as I do 😁