Re: float image viewer

[Nicholas Jankowski]

On Fri, Apr 6, 2018 at 11:37 AM, Richard Kirk <address@hidden> wrote:

Hi.

imshow() is handy because it is always there in Octave. However, there are
things that I need...
- handling of float images
- report of RGB values for pixel at cursor
- dark surround to image

It would be nice to have gamma and range controls. I am happy working with
imshow(I.^0.4) for displaying linear images on a gamma 2.5 monitor, but it
would be nice to get the original floats on a pick, particularly as my
command does nasty things with negative values.

I am currently working on a Mac High Sierra (10.13.3) but I also use CentOS.
I am running Octave 4.2.2.

Here's the first exit point. Perhaps we can do all these and I haven't found
them. I think ImageMagic throttles most things to 8- or 16-bits, so we
cannot see anything outside the 0-1 range. That is fair, as we are sending
the image to a display - we ought to be able to get the float pixel values
from the original image data. I am not needing to do critical colour work on
the images, so even 8-bit RGB would probably do; but the black surround is
important.

I do imaging R&D with floating-point images. I made a very raw floating
point format with 4 32-bit integers as header (magic, channels, lines,
pixels) so we can read it with fread, permute, and reshape. I supported this
in my viewer, and it all works. If you draw a rectangle on the cursor, it
can return the image coordinates or the RGB values. Unfortunately, this
viewer is not open source, and is not very lightweight.

Exit point two: if these features are in the pipeline, I can keep my viewer
for now, and wait. I have something that works for now.

I found 'giv' ( http://giv.sourceforge.net/giv/ ) This seems to have support
for 32-bit float image data, custom formats, and lots of overlays. This
might be an open source solution. I haven't managed to build it on the Mac
yet, but I only found it this morning. I don't think using 'xv' helps but I
have hacked 'xv' ages ago, so I might see what it can do.

compatibility question: are you or anyone else on here familiar with whether Matlab or it's Image toolbox provide any of those functions, and if so how? Are any of these currently not possibly in Matlab that we'd be creating new functionality unbounded by the compatibility concern?  I could run some quick script tests to find out if someone could generate a minimal test.

nickj