Progress on Illuminance

Savanni D'Gerinel 16 May, 2014

I started the Illuminance project back in February of this year. Immediately after my last contract ended, I started working on the code in order to make this application real.

Three months in, I both exault in everything I have learned, and despair at how much remains to be done. This looked like such a simple problem, yet in its solution I have pursued so much new information that I constantly swim underneath a bare understanding of all that I have learned.

Where am I now?

User Interface

I have a very basic user interface that allows me to load images, see their previews, see error messages that occur during load, and run a “naive” HDR calculation. Error messages get displayed in the location where an image preview would normally be. While this is not necessarily elegant, it allow me to display an error that is specific to one image, since a lot of things happen in parallel and in other threads.

Generally, no expensive operation occurs in the main gui thread, so the gui does not ever actually hang. I have not been able to test this exhaustively and I am sure that I will find places where I am wrong, but this does certainly seem to be the case.

Images load in millisecond time, even very large images. They also load with reasonable space usage. I had some great success with creating my own image codec library and representation, but then I discovered that a combination of JuicyPixels and Repa solve the problem better by virtue of being more complete.

On the HDR Calculation

I have spent a vast amount of time learning math in the hopes that I could figure out how to set up the HDR calculation. Ultimately, I read some Matlab code that somebody else wrote to figure out how to set up all of the terms for the problem.

I put all of that together, set up the matrices to solve, called into the LaPack sgelsd function to actually run the calculation… and got the wrong answer. I am stumped, however there is a lot that I can play with still. I have before solved problems where the wrong answer cannot be reverse engineered and where fixing the problem can only be done by carefully examining the inputs. I imagine that is what will be required here.

I do have what I call a naive calculation in the application. This calculation scales every pixel by the associated exposure value, and then averages the result. The end result is weird in the visual artifacts and doesn’t actually give me a high dynamic range anything. While I could improve this, all I wanted to do was to get something on the screen. I have since focused all of my efforts on getting the real calculation to work.

What needs to be done

Oh so much.

  • Get the HDR calculation actually working
  • Be able to save and load HDR files
  • Tonemapping to LDR
  • Making a nice GUI

sigh. In other words, what is done so far only barely scratches the surface of a complete application.


In any event, I am diverting to a different task. Problems on Linux have left all of the current photo managers unusable, and have left me unable to even submit a bug report on the one that I’ve been using for several years, so I am scrambling to hack one out on my own. I have no idea whether this is going to work, because while I can handle most everything, there are GUI elements that I don’t know how to handle yet. We shall see. This does, however, put Illuminance on hold, but all of my photography is really on hold due to these bugs.

  • Shotwell – Ug. Doesn’t handle XMP files. Won’t update tags on a RAW file of any kind. Instead, squirrels tags away in some custom database in a hidden folder so that no other program can see them. This problem burned me very badly once, so I refuse to use the program again unles full XMP support gets added.
  • Digikam – An 8 million pound gorilla (requiring a full installation of KDE) that I’ve been using with good success for a couple of years. Writes all tags for RAW files into an XMP sidecar, so I haven’t lost a tag in years. Unfortunately, it is also crashing randomly with either the Abort signal (and no reportable stack trace) or a Segmentation Fault (which might be reportable as soon as I get symbols installed). I think the problem lies somewhere in the KDE libs, not in Digikam itself. Either way, the application is unusable and I have no way forward to fixing it.

So, maybe I can produce something a little lightweight. I’d been thinking of trying, anyway, but I had not intended to do so until Illuminance was done. Hopefully I will get results faster since this is just a GUI and data management problem.

Dreamer, Shaper, Seeker, Maker