The CIEL*a*b* color space

            How well do these colors match? Close? Not at all? Everyone sees color a little differently. Different light from different times of day or weather conditions will make color look different. Or after looking at the same color over and over one person will begin to see it less acutely.  What is needed is a standard way to talk about color and how well one item matches another.

            A color map to use for color: Below is the CIIELAB color space. “CIE” stands for Commission Internationale de l’Eclairage. That is color research institute that first published this color space in 1976. L*a*b* or LAB are the three coordinates required to map a color within this space. The CEILAB space is a three dimensional globe or cylinder. At the north pole is white and at the south pole is black. Around the equator is a color wheel. L* stands for luminosity (white to black) and is the north / south coordinate. a* is red to green or right to left within the color space. And b* is blue to yellow or in/out.

            This color space is just a way to think about color and is called upon to map and compare colors for quality control purposes in manufacturing and industry to determine how closely two colors match. The two colors being compared, the Target color and the Sample color, each have a place within this map and coordinates (L*a*b*) used to describe their respective positions. In industry the most important measurement within this map is the Delta E or Delta Euclidian distance between the two colors being compared. Delta E is the “as the bird flies” distance between Target and Sample. Instead of describing the difference as 2 down, 3 back and 1 over, the distance is described with a straight-line distance reading for DE or Delta E. A DE of 1 or less is defined as the difference that is not visible to the human eye. A DE of greater than 1 is visible to the human eye. 

The human eye may see around 6,000,000 colors. The PocketSpec ColorQA can see over 16,000,000 different shades of color. Normally when comparing two colors there will be a difference shown on the CEILAB map when using a color reading instrument such as the PocketSpec ColorQA. Delta E is an expression of the number of neighboring colors that could be accepted by the customer and allows the software user to reject colors outside of the acceptance zone.

            How should you talk about color with your customers? When specifying color it is important to establish a concrete color that is acceptable to the customer. Describing a color as Pantone such and such number is not the best way to do it. Your Pantone color deck and theirs may differ and color will appear different when different textures or materials are used. If asked to produce a color in the Pantone color deck, it is best to give the customer a manufactured piece to qualify as acceptable. Once this is done, the actual manufactured piece should be kept away from light and in a very cool place. This becomes the “Target” color and the reference for the future. Measure THIS piece when establishing your Target. It is wise to measure the exact same part of your Target and Sample, because even a small deviation in thickness of the part can change the reading.

Also it is not accurate to describe your color with L*a*b* coordinate readings because there may be small variances in these readings for device to device. Use only the specification of  “a color” <an actual object marked for reference> with an acceptable range of Delta E of <a DE number such as 1.5 or 2, for instance>. Delta E should remain rather constant form one type of color reader to another.