True color measurement: What is the difference between the “true” color of an item and its “perceived” color (by the human eye)?

True color measurement vs. perceived color

Just like Distinctness Of Image (DOI) and Reflected Image Quality (RIQ) are better than traditional gloss measurements when you want to assess the perceived “shininess” of a surface [1], there are several ways to measure color. It may come as a surprise to you but color is not an absolute value.  We will explain further on the concept of true color and perceived color.

The human brain only works on perceptions with no absolute reference or base line. On top of that, everybody has a very unique sense of color based on the effectiveness of our light receptors (cones). Scientists tried to put numbers on colors (just like they defined time, mass or distance) but how many of us will refer yellow as the 589 nm D line of sodium?

Now comes the tricky part: even if we can define the “true” color of a pure yellow (whatever that is), the same pure yellow, defined with standard LYellow, aYellow, bYellow [2] values as can be measured by ASTM D2244 test,  will appear differently depending on the surface condition of the object (texture and gloss).

Just like glossmeters can now  measure DOI and RIQ, new generations of spectrophotometers can be set to take into account (or not) the specular component [3] in order to measure, respectively, the true color or the perceived color of an object.

True color measurement

To measure the true color of an item, all the reflected light must be captured, regardless of the reflection angle (specular, scattered or diffuse) [4]: therefore, this type of measurement is called: SCI (Specular Component Included)

Perceived color measurement

To measure the perceived color of an item, the specular component (which is usually the dominant type of reflection) is excluded to make the result more sensitive to scattered light caused by the surface conditions (gloss and texture): therefore, this type of measurement is called: SCE (Specular Component Excluded).

[1] Please refer to our presentation “Beyond Gloss…” for more info on this specific topic
[2] L.a.b. coordinates refers to the color measurements taken in a system called the “L.a.b. sphere” as shown below:

[3] Specular reflection is the perfect reflection (Incoming and outgoing beams have the exact same angle)
[4] “Categories” of reflections :