Coming up with a Colorimeter Strategy for 3D Prints

 I used the Behr swatches as a staring place, because paint comparison is exactly the application the manufacturers had in mind when designing their products.  Paint swatches are professionally printed uniformly on smooth surfaces.  Thus, they provide a good starting place with which to compare the performance of the colorimeters I own.

3D prints, on the other hand, are NOT uniform surfaces.  They are, by the very nature of the way they are produced, corrugated in form, reflecting light in lines of brightness and darkness in a photo.  Here, for instance, is the bottom of our test print we are using for our colorimeter work.

Bottom of 3D Print Sample

 

The corrugated nature of the 3D print is plain to see,  And, it's easy to imagine that the very nature of the surface would make at least SOME difference in our colorimeter readings.

We can minimize this effect by smoothing, to some extend, by "Ironing" the top surfaces of our test objects.  Here is the top of our test object that has been 'Ironed" to increase smoothness.

"Ironed" top of 3D Print Sample

 

While not as perfect as the surfaces of our Behr color samples, it is at least somewhat improved.  Given the differences in surface quality I decide to test whether these two surfaces return measurably different results.

The LS170 was selected for this test because of the lighting/capture system it uses. 

The LS170 relies on a 45°/0° capture system, meaning the lighting hits the target at an angle of  45° and the camera capture directly from above at 0°.  

 I wondered if the lighting angle might reflect differently in one orientation as apposed to another due to the artifacts in the 3D print.  So, I also decided to see if rotating the LS170 90 had any affect on the outcome.

This meant each sample would be tested 4 times.  The top would be sampled twice, at 0° and 90° as would be the bottom.  The LS170 lends itself to this reorientation due to it's square shape. 

The differences (Delta) between the published Bambu color specs were then calculated for each test. 

THE RESULTS

Five different Bambu Labs filaments were selected for testing.  The goal was to compare the results between the ironed top and raw bottom of the print sample.  Each of these were tested twice by rotating the LS170 by 90°. The differences (Delta) between the published Bambu color specs were then calculated for each test.  (Click on image for the full size)

While these results haven't been fully analyzed, it seems clear that the ironed top surface generally produces smaller differences than the bottom counterparts.  What is obviously clear is that LS170 ALWAYS returns a darker shade than the specs of the target color.  It's not enormous, in most cases; but, visible in the samples.

I was actually quite surprised that rotating the LS170 didn't seem to make all that much difference in the results. 

We plan to run the same test using the LS173, which relies on a different lighting/capture system, before scanning all of our current inventory.  I suspect our Delta values will be much smaller overall.  But, I do NOT expect to ever match the target specs.  These best we might be able to do is come up with a uniform offset that can applied.  More importantly, as the library of color samples continues to grow on FilamentColors.xyz, we will be building our own library of colors for entering into their search engine.  And, we will have the tools to locate a closely matching color should we need to search for one.

UPDATE 

After my initial posting of this article, I realized that it was a major oversight not to have included the color "Basic Black: in my tests.  So, here it is:

Why this is an important inclusion is that it gives us the bandwith of the colorimeter.  By sight we can see that Bambu Black is as black as one could expect.  Yet it does NOT register as uniform zeros across Red, Green and Blue by the colorimeter.  The light source of the colorimeter is bright enough, and the surface reflective enough,  to register almost 50 units above zeros across the spectrum.

When we combine this with the readings of around 20 points LOWER for white than we might expect, it's clear that, at least when measuring rough surface plastics, the bandwidth of the colorimeter is less than the full spectrum.  This is common in all digital photography.  Professional photographers use a histogram to pull blacks down and whites up to achieve the proper contrast.  

It doesn't matter all that much if our goal is simply to compare a specific color of one brand against another as long as we use the same colorimeter using samples printed in the very same way.