A Delta E of 4 is the upper threshold for acceptable machine repeatability or consistency.ĭelta E provides a value indicating the overall difference between two colours. Smaller differences can normally be detected in neutral colours (such as our samples), while more saturated colours require a slightly larger Delta E. The minimum Delta E for seeing a difference is about 2. Could we detect that difference if we were viewing those two colours? Probably just barely. The Delta E (difference) between our two colours is 3. Colour 1 has a Lab value of 51, 2, 2 and Colour 2 is 50, 0, 0 (right at the centre of the colour space):Īdd them together: and take the square root. Let’s try a simple example to see what we get. Written out as a formula it looks a little more daunting. We square the difference between each of the L, a, and b values add them all together and take the square root of that sum. How do we do that? It looks a lot like the formula used to determine the long side of a right triangle that you may remember from high school geometry. With values assigned to each of the L, a, and b attributes of two colours, we can use simple geometry to calculate the distance between their two placements in the Lab colour space (see Figure 4.7). Delta E is the difference between two colours designated as two points in the Lab colour space. Delta E Figure 4.7 Lab Colour Spaceĭelta, the fourth letter of the Greek alphabet and symbolized as a triangle, is used in science to indicate difference. That yardstick is the Delta E measurement. We can’t make any progress in evaluating our success in colour matching unless we have a frame of reference, some yardstick to determine how much one colour sample is similar or different from another. Now it’s time to explore the practical application of this colour map for the comparative analysis of colour samples. For a visual depiction of the Lab colour space, open the ColorSync application found in the Utilities folder of any Macintosh computer and view one of the default profiles such as Adobe RGB. The most saturated colours are at the extremes of the a and b axes, in both the large positive and negative numbers. Imagine that equivalent values of the opposing colours are cancelling each other out, reducing the saturation and intensity of those colours. For correct placement, remember that red is on the right, and blue is on the bottom.Ĭolours are more neutral and grey toward the centre of the colour space, along the L axis. If you found our previous mnemonic aid of POLO helpful, you can use RGBY to remember the colour pairs. This places red to the right, green to the left, blue at the bottom, and yellow at the top. The standard two-dimensional depiction is of only the a and b axes, with a as the horizontal axis and b as the vertical axis. In contrast, the a and b axes are chromatic, describing the colour character and the type of light.

Here we are dealing with the volume rather than the kind of light. The L axis is considered achromatic meaning without colour. Notice that there are no negative values on the L axis as we can’t have less than zero light, which describes absolute darkness. It’s comprised of three axes: L represents darkness to lightness, with values ranging from 0 to 100 a represents greenness to redness with values of -128 to +127 and b represents blueness to yellowness also with values from -128 to +127. In section, 4.2, we mentioned the Lab colour space as a natural outgrowth of understanding the function of opponency in human vision. The latter two are particularly important for colour management.

Three core definitions provided by the CIE are the standard observer, the Lab colour space, and Delta E measurements. The CIE (Commission Internationale d’Eclairage or International Commission on Light) is a scientific body formed by colour scientists in the 1930s that has provided much of the fundamental colour knowledge we possess today. Colour Management in the Graphic TechnologiesĤ.4 Lab Colour Space and Delta E Measurements

Chroma lab