Some of my colleagues at work have been asking me this question and I’ve been responding by vaguely saying the right words and waving my hands around. So I’ve done what they should have done (and I should have done before them!) and gone to the interweb for the relevant information. The first hit is the Panotools wiki page on Enfuse.
Enfuse is based on a paper written by Tom Mertens, Jan Kautz and Frank Van Reeth, in which you’ll find much more detail than I’ll be providing here. As the page explains, the basic premise to enfuse is to compare overlapping input pixels and to filter the best information from among them through to the output pixels. So how does it choose the “best” ones. It uses criteria based on exposure, saturation and contrast.
- exposure : it chooses those pixels which are closest to the middle of the range as those are considered the best exposed;
- saturation : here, enfuse favours the most highly saturated pixels;
- contrast : again, those pixels which are going to provide the highest contrast are favoured. It uses the local standard deviation as a metric for contrast.
On top of all this, the problem that the Enfuse algorithm needs to solve is to arrive at the best solution that satisfies these criteria and produces a smooth resultant image.
In the Lightroom plugin to Enfuse, the relative importance of these three criteria can be controlled with sliders in a window. Shown below are the recommended defaults that I’ve been using, and haven’t ventured from. I need to explore these a bit more (for instance, why is contrast given a zero weight?). There are also advanced options to investigate, but may or may not actually prove useful.
Expect more as and when I learn it. In the meantime, for comparison you can see the original image to that above of the Halema’uma’u plume, heading towards Hilo and as seen from Mauna Kea, in this earlier post.
On the way down from the summit after finishing for the night we noticed something spectacular.
It wasn’t a great night – it was cloudy throughout which closed off the other optical and infrared telescopes, but because the JCMT is a submillimetre (i.e. sensitive to microwave radiation) telescope we can see through the clouds. However, the stability and ‘wetness’ of the atmosphere above us was poor, so although we could work it wasn’t great.
It was cloudy above but it was clear down to the coast and we had a great view of the volcano. In these pictures you can see the plume of volcanic emissions coming from the Halema`uma`u vent from the top of Kilauea volcano. Tom had some nice pictures of it close up when he went on his ‘shopping trip’ this weekend. The pictures below aren’t as clear as I would like (click on them to get a better look) as the Sun hadn’t fully risen yet so getting the right exposure (bright sky & dark ground) was tricky as I wanted to try and preserve some of the colour in the sky – I’ll see if I can improve them a bit when I get them into Lightroom on my return home.
I never cease to be humbled by the place we are privileged to call our workplace. It always gets me as we drive down from the summit, the fact that we are (usually) looking down onto the cloud tops rather than up. In these images we are looking down onto another volcano as its exhaust plume is carried away by the wind.
Ah, but notice, where is that plume heading? Not out to the ocean as usual. That’s because the trade winds that usually come in from the east and carry the vog (a uniquely Hawai’ian term, I believe, for ‘volcanic fog’) out to the ocean and beyond (and affecting the sky lines and respiratory systems of folks on our neighbour islands) are not there. Not this day. The winds were coming from the west (we call them ‘Kona winds’) and carrying the vog straight to Hilo!
I spoke with Mila that afternoon and she said that the vog was particularly bad that day…. no wonder.