Guide: How To Project a Test Pattern


Sometimes you may want to test your projector to see whether it’s in focus and projecting properly. Ember has a few built-in test patterns that you can call from the command line via SSH. Here’s how to use them:

NOTE: the last print made on your Ember must be a Video Mode print. If the last print was a Pattern Mode print, you’ll need to start and then cancel a Video Mode print before projecting a test pattern, or else it will not display properly. If you don’t know what Pattern Mode is, then you don’t need to worry, as Video Mode is the default.


First, connect to your printer via SSH.

This calibration image is the most commonly-used test pattern, and it can be called by typing the following:


Because its lines are very thin, you can use it for both focusing and aligning the projector. Here’s what to look for:

  • The lines are in focus at the surface of the PDMS window in an empty resin tray
  • The white dashes at the top and bottom are the within the window

If both of the conditions above are true, your projector is aligned.

If it’s out of focus, you can use a 2.5mm hex key to turn the projector focus screw just above the power plug. All projectors are aligned and focused at the factory, so you should only need to adjust it if you’ve removed the projector or otherwise modified your Ember’s optics.

When you’re done using it, type the following to turn it off:

echo showblack > /tmp/CommandPipe

If you’re doing a full calibration of your projector, you’ll probably want to use the next test pattern to calibrate your projector’s irradiance.

[Scroll down, below the all white image inserted below.]

First, connect to your printer via SSH.

This test pattern is an alternative to using the standard exposure test (exp_test.tar.gz (876 Bytes)
) used when calibrating a projector’s irradiance. It’s more convenient because you don’t have to wait for the build arm to descend before you can test your projector’s irradiance. To use it, type the following:

echo showwhite > /tmp/CommandPipe

When you’re done using it, type the following to turn it off:

echo showblack > /tmp/CommandPipe


First, connect to your printer via SSH.

This is our original test pattern that we’ve kept around just because it’s occasionally useful for various things. It shows the extents of the projected image on all sides (the white dashes). To project this test pattern, type the following:

echo test > /tmp/CommandPipe

When you’re done using it, type the following to turn it off:

echo showblack > /tmp/CommandPipe


If you’d like to use a different image as a test pattern, you can do so by copying a PNG file from your computer to ember’s /var/smith directory using scp on Mac or PSCP on Windows.

First, connect to Ember via SSH/PuTTY and rename the existing test pattern in case you want to switch back:

mv /var/smith/TestPattern.png /var/smith/TestPattern.png.old

Next, follow the instructions for your operating system below.


  1. Connect to Ember via USB
  2. Open Terminal (it’s in the Utilities folder inside Applications)
  3. Type (all on one line) scp -r /path/to/your/testimage.png root@
  4. If prompted, type yes to add your printer to the list of known hosts


  1. Connect to Ember via USB
  2. Download PSCP
  3. Open a Command Prompt (hit Windows Logo Key + R, then enter cmd into the Run box)
  4. Navigate to where you downloaded PSCP
  5. Type (all on one line) pscp -r c:\path\to\your\testimage.png root@

Now when you use Test Pattern #3, it will display your custom image instead. I’ve grown fond of using this one:

It shows individual pixels and is really good for doing fine focus.


Be aware:
The printer / projector must have run in ‘video mode’ before using this test pattern. If your last print used ‘pattern mode’, you will need to at least load and start (then cancel) a ‘video mode’ print.

TIP: lay a small piece of white paper on a dry PDMS window to really see the image clearly. I don’t vouch for it’s use to actually adjust the focus, but it sure makes seeing the image a lot easier.


Thanks for helping discover that issue, and for the tips. I’ve updated the post above with the new info, plus how to upload a custom test image.


Tried to download the test pattern and was prompted for login into something called Discourse… What’s that about?


That’s weird, you should just be able to click on it to view it full size, then either click Download or right-click and choose Save As. Do neither of those work? They both work for me even when I’m not logged in.


When I click the image, it pops up full size, with a little "download’ link down at the lower left of the image. When I click the link, it get the ‘Discourse’ login. Hadn’t tried the typical ‘Save As’ simply because I saw the link and assumed it would download a .png file. But that works - so YAY me!