Question: Visualizing high resolution image is slow

[mdhe1248]

When visualizing a high resolution image, ImageView seems quite slow (slower than ImageJ). To speed up, is it possible to limit the image resolution to that of monitor; but visualize the original resolution when a region is zoomed in? I guess when the image resolution is larger than that of monitor, it may not necessary to load all the pixels.

[jwahlstrand]

I'd assume the slowness has to do with ImageView using Cairo to draw an image into a memory buffer, which is then shown by GTK. There's little to no GPU involvement, as far as I understand it. There are probably ways to eke out more performance within the current approach (perhaps by doing what you say), but it would probably be more efficient to use GL or the equivalent to do the rescaling and drawing. That would require someone rewriting the Canvas code in GtkObservables to use GL rather than Cairo.

[mkitti]

With ImageJ is an image pyramid being used (such as with BigDataViewer) ?

[jwahlstrand]

Over the summer I did some profiling of ImageView's rendering of big images and found that for the "earth" test image, almost 90% of the time in the canvas "draw" function was spent calling restrict, which downsamples the image. Doing the same downsampling over and over as the user zooms and pans is wasteful, and caching the output indeed improves performance of redraws (#313). However, it turns out that a real implementation of an image pyramid is in the works (JuliaImages/ImageBase.jl#39). Rather than hacking something together in this package, it makes sense to wait and use whatever comes out of that effort.