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notes biology

True Facts: Sea Stars

The latest True Facts about Sea Stars is unmissable. The video is filled with delightful echinoderm biology and even covers some recent discoveries on these enigmatic creatures. Watch it!

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imaging articles code

ImageJ macro to synchronize and combine image stacks

The embryos I study rarely develop in perfect synchrony. That means that when I film them under the microscope some embryos will be younger—or older—than others.

ImageJ macro with Drosophila embryo
Using an ImageJ macro to help me analyze movies of Drosophila embryos.

For this reason, I often need to synchronize the recordings to make sure they all begin at the same embryonic stage. When the movies are synchronized I can combine them side-by-side, and it becomes much easier to compare and spot differences between two embryos.

ImageJ macros save time

Combining movies in Fiji/ImageJ is straightforward using the Combine... command. But synchronizing is way harder. It depends on human classification and involves some calculations and stack juggling that can (and will) become tedious.

To help me out, I wrote a small ImageJ macro available here: SyncAndCombineStacks.ijm. Follow below to see how it works.

Combined movies without syncing

That’s what unsynchronized movies look like. I combined them fresh off the microscope without any synchronization:

Two embryos of the fruit fly Drosophila melanogaster. Both were acquired in the same microscopy session. The top embryo is older than the bottom embryo.

Combined movies after syncing

Here are the same two movies now synchronized by the embryonic stage:

The same two embryos are now synchronized.

How it works

The macro performs the hard work. It calculates how many frames to trim from each stack. Then it duplicates the selected range of frames common to both stacks. Finally, it combines the synchronized recordings into a single image stack. All you need to do is to select the corresponding frames between the two stacks.

Step-by-step instructions

Here are the instructions step-by-step:

  1. Open both image stacks in ImageJ.
  2. Adjust the contrast if needed (before running the macro).
  3. Select a reference frame in the top stack (e.g. stage easy to recognize).
  4. Select the correspondent frame in the bottom stack.
  5. Run the macro and fill in the dialog parameters.
  6. Click OK, wait a few seconds, and check if the synchronization is good. Otherwise, re-run with different parameters.

Screencast

I’ve also recorded a small screencast:

Note! The macro does not touch the original stacks, but it outputs an RGB Color stack. There are a couple of reasons for that. Converting to RGB avoids contrast issues when the stacks have different pixel intensities. It also prevents quirks in video players that can’t handle 16-bit movies. But if you need to perform image analyses on the final stack, remove this option. I may add a checkbox for that in the future.

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articles code

Convert video to animated GIF

Something that I began doing more often is converting videos of developing embryos or marine invertebrates to animated GIFs. But how to do this conversion without affecting the quality of the video?

A jellyfish moving its tentacles. Source: Cifonauta.

Some time ago I found this guide to convert videos to high-quality animated GIFs using the tool FFmpeg. The trick is to generate a color palette based on the original video to improve the color quality of the GIF. Based on this guide I created a small bash script to make my life easier and perhaps yours too ;)

Check it in https://github.com/nelas/gif.sh

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notes biology

Living entoprocts

Live footage of entoprocts! Tiny colonial invertebrates that capture food with a crown of ciliated tentacles

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biology imaging notes

Fruit fly embryo under lightsheet microscopy

A short video that I made about the embryonic development of the likeable Drosophila, also known as fruit fly or vinegar fly, won an honorable mention in the Small World in Motion.

A single embryo imaged from four different angles.

The details on the techniques I used and the video on its full resolution are available for download and re-use on the Wikimedia Commons.

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biology notes

Understanding the evolution of cleavage patterns in early embryonic development

Video summary about our work on bryozoan development and the evolution of cleavage patterns published in BMC Biology!

The video was produced by Research Square. Also available on Vimeo.

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biology imaging notes

Bryozoan embryos viewed from the animal and vegetal poles

The first 24 hours in 1.5 minutes of bryozoan embryos.

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notes biology imaging

Bryozoan embryos viewed from the animal pole

Categories
notes biology imaging

Young nemertean learning to hunt

Young nemertean worm Lineus ruber learning to hunt eggs of the annelid worm Platynereis dumerilii.
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biology notes

Life Between Grains

All sorts of worms live a Life Between Grains #WormWednesday Fantastic production by CEBIMar, @Maik2DD and others.