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In Silico Flurries: Computing a world of snow. Scientific American. 23 December 2017


visualization + design

Martin Krzywinski @MKrzywinski mkweb.bcgsc.ca
Cover image accompanying our article on mouse vasculature development. Biology turns astrophysical. PNAS 1 May 2012; 109 (18) (zoom, PNAS)

Creating the PNAS Cover

One of my goals in life, which I can now say has been accomplished, is to make biology look like astrophysics. Call it my love for the Torino Impact Hazard Scale.

Recently, I was given an opportunity to attend to this (admittedly vague) goal when Linda Chang from Aly Karsan's group approached me with some microscopy photos of mouse veins. I was asked to do "something" with these images for a cover submission to accompany the manuscript.

When people see my covers, sometimes they ask "How did you do that?" Ok, actually they never ask this. But being a scientist, I'm trained me to produce answers in anticipation of such questions. So, below, I show you how the image was constructed.

The image was published on the cover of PNAS (PNAS 1 May 2012; 109 (18))

Tools

Photoshop CS5, Nik Color Efex Pro 4, Alien Skin Bokeh 2 and a cup of coffee from a Rancilio Silvia.

source images

Below are a few of the images I had the option to work with. These are mouse embryonic blood vessels, with a carotid artery shown in the foreground with endothelial cells in green, vascular smooth muscle cells in red and the nuclei in blue.

Of course, as soon as I saw the images, I realized that there was very little that I needed to do to trigger the viewer's imagination. These photos were great!

Martin Krzywinski @MKrzywinski mkweb.bcgsc.ca
Mouse carotid arteries. (zoom)
Martin Krzywinski @MKrzywinski mkweb.bcgsc.ca
Mouse carotid arteries. (zoom)
Martin Krzywinski @MKrzywinski mkweb.bcgsc.ca
Mouse carotid arteries. (zoom)
Martin Krzywinski @MKrzywinski mkweb.bcgsc.ca
Mouse carotid arteries. (zoom)
Martin Krzywinski @MKrzywinski mkweb.bcgsc.ca
Mouse carotid arteries. (zoom)
Martin Krzywinski @MKrzywinski mkweb.bcgsc.ca
Mouse carotid arteries. (zoom)
Martin Krzywinski @MKrzywinski mkweb.bcgsc.ca
Mouse carotid arteries. (zoom)
Martin Krzywinski @MKrzywinski mkweb.bcgsc.ca
Mouse carotid arteries. (zoom)
Martin Krzywinski @MKrzywinski mkweb.bcgsc.ca
Mouse carotid arteries. (zoom)

memories of star trek

Immediately I thought of two episodes of Star Trek (original series): Doomsday Machine and the Immunity Syndrome, as well as of images from the Hubble Telescope.

Martin Krzywinski @MKrzywinski mkweb.bcgsc.ca
Enterprise is about to be consumed by a horror tube: a planet killer! (The Doomsday Machine)
Martin Krzywinski @MKrzywinski mkweb.bcgsc.ca
Enterprise heads into a giant amoeba. Who eats whom? I'll let you guess. (The Immunity Syndrome)
Martin Krzywinski @MKrzywinski mkweb.bcgsc.ca
Orion nebula (M42) as seen by the Hubble telescope. (zoom)

I though it would be pretty easy to make the artery images look all-outer-spacey. They already looked it.

centerpiece image

And then I saw the image below.

Martin Krzywinski @MKrzywinski mkweb.bcgsc.ca
A particularly spectacular image of a mouse carotid artery. I'm thinking 10 on the Torino scale. (zoom)

constructing the cover

background

The background was created from the two images shown here. The second image was sampled three times, at different rotations.

Martin Krzywinski @MKrzywinski mkweb.bcgsc.ca
Images used for background. (zoom)
Martin Krzywinski @MKrzywinski mkweb.bcgsc.ca
Images used for background. (zoom)
Martin Krzywinski @MKrzywinski mkweb.bcgsc.ca
Layer composition for background elements. (zoom)

The channel mixer was used to remove the green channel and leave only red and blue.

Martin Krzywinski @MKrzywinski mkweb.bcgsc.ca
Background elements for PNAS cover image. (zoom)

middle ground

The next layer was composed of what looked like ribbons of blue gas. This was created by sampling the oval shapes from the source images. Here the red channel was a great source for cloud shapes, and this was the only channel that was kept. The hue was shifted to blue and a curve adjustment was applied to increase the contrast.

Martin Krzywinski @MKrzywinski mkweb.bcgsc.ca
First set of middle ground elements, before adjustments. (zoom)
Martin Krzywinski @MKrzywinski mkweb.bcgsc.ca
First set of middle ground elements, after channel adjustments. (zoom)
Martin Krzywinski @MKrzywinski mkweb.bcgsc.ca
Second set of middle ground elements. (zoom)
Martin Krzywinski @MKrzywinski mkweb.bcgsc.ca
Layer composition for middle ground elements. (zoom)

When the foreground and middle ground elements were combined, the result was already 40 parsecs away.

Martin Krzywinski @MKrzywinski mkweb.bcgsc.ca
Background and foreground elements for PNAS cover image. (zoom)

foreground

The foreground was created from the spectacular comet-like image of a mouse artery. Very little had to be done to make this element look good. It already looked good.

I applied a little blur using Alien Skin's Bokeh 2 to narrow the apparent depth of field, masked out elements at the bottom of the image and removed some of the green channel. The entire blue channel was removed altogether (this gave the tail of the comet a mottled, flame-like appearance).

Martin Krzywinski @MKrzywinski mkweb.bcgsc.ca
Foreground element, before adjustments. (zoom)
Martin Krzywinski @MKrzywinski mkweb.bcgsc.ca
Foreground element, after channel adjustments. (zoom)
Martin Krzywinski @MKrzywinski mkweb.bcgsc.ca
Layer composition for foreground element. (zoom)

post processing

Martin Krzywinski @MKrzywinski mkweb.bcgsc.ca
Initial composition of background, middle ground and foreground elements. (zoom)
Martin Krzywinski @MKrzywinski mkweb.bcgsc.ca
40% localized application of Nik's Tonal Contrast (Color Efex 4 plugin) to increase structure in red channel. (zoom)
Martin Krzywinski @MKrzywinski mkweb.bcgsc.ca
50% blend with Nik's Pro Contrast (Color Efex 4 plugin). (zoom)

And here we have the final image.

Martin Krzywinski @MKrzywinski mkweb.bcgsc.ca
Final PNAS cover. Spacey! (zoom)
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news + thoughts

Machine learning: supervised methods (SVM & kNN)

Thu 18-01-2018
Supervised learning algorithms extract general principles from observed examples guided by a specific prediction objective.

We examine two very common supervised machine learning methods: linear support vector machines (SVM) and k-nearest neighbors (kNN).

SVM is often less computationally demanding than kNN and is easier to interpret, but it can identify only a limited set of patterns. On the other hand, kNN can find very complex patterns, but its output is more challenging to interpret.

Martin Krzywinski @MKrzywinski mkweb.bcgsc.ca
Nature Methods Points of Significance column: Machine learning: supervised methods (SVM & kNN). (read)

We illustrate SVM using a data set in which points fall into two categories, which are separated in SVM by a straight line "margin". SVM can be tuned using a parameter that influences the width and location of the margin, permitting points to fall within the margin or on the wrong side of the margin. We then show how kNN relaxes explicit boundary definitions, such as the straight line in SVM, and how kNN too can be tuned to create more robust classification.

Bzdok, D., Krzywinski, M. & Altman, N. (2018) Points of Significance: Machine learning: a primer. Nature Methods 15:5–6.

Background reading

Bzdok, D., Krzywinski, M. & Altman, N. (2017) Points of Significance: Machine learning: a primer. Nature Methods 14:1119–1120.

...more about the Points of Significance column

Human Versus Machine

Tue 16-01-2018
Balancing subjective design with objective optimization.

In a Nature graphics blog article, I present my process behind designing the stark black-and-white Nature 10 cover.

Nature 10, 18 December 2017

Machine learning: a primer

Thu 18-01-2018
Machine learning extracts patterns from data without explicit instructions.

In this primer, we focus on essential ML principles— a modeling strategy to let the data speak for themselves, to the extent possible.

The benefits of ML arise from its use of a large number of tuning parameters or weights, which control the algorithm’s complexity and are estimated from the data using numerical optimization. Often ML algorithms are motivated by heuristics such as models of interacting neurons or natural evolution—even if the underlying mechanism of the biological system being studied is substantially different. The utility of ML algorithms is typically assessed empirically by how well extracted patterns generalize to new observations.

Martin Krzywinski @MKrzywinski mkweb.bcgsc.ca
Nature Methods Points of Significance column: Machine learning: a primer. (read)

We present a data scenario in which we fit to a model with 5 predictors using polynomials and show what to expect from ML when noise and sample size vary. We also demonstrate the consequences of excluding an important predictor or including a spurious one.

Bzdok, D., Krzywinski, M. & Altman, N. (2017) Points of Significance: Machine learning: a primer. Nature Methods 14:1119–1120.

...more about the Points of Significance column

Snowflake simulation

Tue 16-01-2018
Symmetric, beautiful and unique.

Just in time for the season, I've simulated a snow-pile of snowflakes based on the Gravner-Griffeath model.

Martin Krzywinski @MKrzywinski mkweb.bcgsc.ca
A few of the beautiful snowflakes generated by the Gravner-Griffeath model. (explore)

The work is described as a wintertime tale in In Silico Flurries: Computing a world of snow and co-authored with Jake Lever in the Scientific American SA Blog.

Gravner, J. & Griffeath, D. (2007) Modeling Snow Crystal Growth II: A mesoscopic lattice map with plausible dynamics.