Finally, click Image → Stacks → Z Project, and
choose Max Intensity to add up the brightest
pixels from each frame.
D. COLOR-CODING TIME: STAR
PATHS ACROSS THE NIGHT SKY
I made a time-lapse film of the stars passing
over my yard from dusk to dawn. (I used a
Canon camera hacked with open source Canon
Hack Development Kit, or CHDK, software to
do long-exposure time-lapse recording).
I used ImageJ to make a black and white
film of only the moving objects by subtracting everything from each frame that was also
in the previous frame. I then time-coded the
resulting film by color, with purple slowly
turning to yellow.
Lastly, all the colored frames were projected onto a single image. In the final image,
purple objects were the ones visible just
after sunset, and orange/yellow objects, like
the clouds, appeared around sunrise. Stars
moved across the field of view at all times.
E. KYMOGRAPH: MOTHER
ROBIN’S NEST TIME GRAPH
My sons and I found a robin’s nest on our
house, and we were fascinated to have a
peek. So we set up a webcam and watched
the nest. One day we made an all-day, time-lapse recording. The mother sat on the eggs
throughout the day, periodically taking trips
away, presumably for food.
We were curious to see if there were any
obvious patterns to the timing of her trips,
so we made a kymograph, which displays a
single slice of the image along one dimension,
with time running along the other dimension.
The kymograph in Figure E marks the time
in 10-minute intervals along the top, running
from morning at the left to evening at the
right. When the blue of the eggs is visible in
the vertical stripes, the mother bird was out
of the nest, and you can see how the egg
positions changed with each maternal visit.
We had read online that robins never leave
their nests for more than 10–15 minutes at
a time, but it looks like this bird took a long
lunch from around 11: 40 a.m. until noon. It
got dark just before 7 p.m.
sky as birds flew overhead. I then Z-Projected
a 2-second segment, about 30 frames.
Protocol: Open your video. Click on your
video to select it, then click Image → Stacks
→ Z Project, and choose Min Intensity to add
up the darkest pixels from each frame.
Protocol: Open a video, then select the
straight line tool from the row of tool icons,
and click and drag to draw a line over an area
of interest in the video (here, the eggs). Click
Image → Stacks → Reslice to see what happened under that line over time.
Protocol: Open a video. When the “convert
to 8-bit grayscale” option pops up, accept
it. Click on the video to select it, and make
a second video showing only the moving
objects by clicking Plugins → Stacks —
T-Functions → Delta F. To color-code the
time, click Plugins → Stacks – Z-Functions
→ Z Code Stack, and select a color scheme.
F. IMAGE PROCESSING
WITH A SPREADSHEET
You can extract the pixel values from an
image and transform them yourself in a
spreadsheet program like Microsoft Excel.
It’s interesting to see how features like local
contrast can be highlighted this way.
Here, I started with a 50× 50 pixel image
of an acorn (Image 1 above), then generated
several versions using simple formulas in
120 Make: makezine.com/27