(Intensity and Up-Down)
We interpret two dimensional images of three dimensional objects using
shading as a visual cue, assuming light to come from above.
- Load Sample Images / Filter Samples / scaled 06 2000.tiff, a
SEM image of a ductile fracture.
- (This exercise might be repeated with the more easily interpreted Sample
Images / Filter Samples / face.tiff, which does not show the same illusion,
or with the Sample Images / Illusions / Mountains.tiff, where the
illusion is so strong that the image is difficult to interpret when inverted.
- Note the 'hole' in the center.
- Try inverting the pixel values (this is not the operation to give the
illusion, but might be done by mistake, so do it anyway) using the Edit
-> Invert menu.
The 'hole', might still appear to be a hole, although this 'negative'
image is difficult to interpret.
- Invoke the Edit -> Invert menu again to restore the image to its
original form. (Or use the File -> Revert to Saved menu or Edit
- Invert the image using the Edit -> Flip Vertical menu Process
/ Rotate / Flip Vertically.
The 'hole' doesn't look much like a hole any more (at least to me), although
I still can see all the other little 'holes' correctly.