Issues with scaling Gray images of various types about imageview.jl

[timholy]

This is an area I need to document and improve. Scaling of images turns out to be surprisingly subtle. You generally want to take a Uint8 image at face value, but other types may need to be scaled for any kind of sensible display. The ScaleMinMax type is a good general default; however, often one could get by with fewer operations, and at least when I tested it some time ago this can have a measurable impact on movie playing speeds. Hence the other types.

Are you calling this programmatically, or from ImageView's display? If programmatically, my recommendation is to create your own ScaleInfo object. If you want to convert to a Uint8 you can say

uint32color!(buf, img, scaleminmax(img))

If you're calling it from display, then I'm aware this is an area which needs some work. (I'm partway to having a GUI to show a histogram, but other priorities have risen above this one.) For now you should be able to say

display(img, render! = (buf, img) -> uint32color!(buf, img, scaleminmax(img))

If you have a movie, this will auto-scale each image separately. You can fix the range manually with scaleminmax(Uint8, img, minval, maxval) instead of just scaleminmax(img).

Does this help?

[timholy]

See also be64cbe8ba40fdf49374bbd854f223a4516f55c9.

[timholy]

Also, I don't understand how you went from a Uint16 to a Uint64.

[rsrock]

Now that's pretty nifty. I am using display() for now, and your line up above scales my movie display range just right. I'm impressed that display() makes it so easy to define custom renderers like that, I'm going to have to poke around in there some more.

Playback is at ~ 10 fps. I can't seem to get the right-click in the button area to change the frame rate on my Mac, but I don't really need that right now. Overall, pretty useful.

Your other question about Uint16 to Uint64 was actually answered by your changes to Images.jl in be64cbe. I was confused about the promotion to Uint64 with the bitwise &, but Stefan confirms that this is the expected behavior.