SwatchMate Cube, Part 1 - Out of the box accuracy.

Palette/SwatchMate Cube, Part 1 - Out of the box accuracy.

Graeme W. Gill May, 2015.

I've had a few people ask me about the Palette/SwatchMate Cube :- what I think about it, and whether I'm going to support it in ArgyllCMS or ColorMeter.

Partly because it originates in my own town of Melbourne Australia, and also to give some perspective as to where these entry level devices fit into the colour measurement landscape (see also the NODE Chroma module and Nix Color Sensor for roughly similar devices), I decided to buy one and take a closer look at it.

For those not familiar with it, the Palette/SwatchMate Cube made a splash about 18 months ago with a successful Kickstarter crowd-funding campaign to build the first batch of units, and followed up with an Indiegogo campaign to build a second batch. As well as winning a 2013 Melbourne and Sydney Design Award, it garnered a great deal of (sometimes rather breathless) press attention - you could almost be forgiven for thinking that no-one had ever thought of measuring colour before ! From the press and manufacturers information it seems to be a measurement device aimed squarely at graphic artist and interior designers, and looks particularly attractive due to its relatively low cost and great convenience.

I'll make a few comments latter in the article, and go into even more depth in Part 2, but for the moment let's cut to the chase :- how accurate is it ?

Testing Method:

Since this is a Colorimeter rather than a Spectrometer, its accuracy could well be dependent on the particular samples tested, so it's hard to be entirely fair in choosing a test. So I decided to do a fairly uncontroversial test :- benchmark it using the very well known ColorChecker colours. These are 24 matt colours with both a range of colour test patches as well as grey-scale, and having some diversity of spectral composition (i.e. they are not created by a printing process).

Duramax

I also decided to see just how well or poorly it copes with glossy colours, and chose a paint catalogue containing 28 glossy colours that use a classic 4 colour print process with a glossy overcoat (Dulux dura max spray paint catalogue).

As a reference instrument, I used an X-Rite eye-One Pro 2, a well respected graphic arts spectrometer. For comparison, I also test an X-Rite ColorMunki spectrometer, a cheaper spectral instrument. I calculate the colour differences using two units, the well known Delta E 1976 (which is simply the difference in the L*a*b* perceptually uniform colourspace), and the more perceptually accurate CIE Delta E 2000. 1 delta E corresponds to a "Just Noticeable Difference" in colour. All measurements were for a standard graphic arts conditions of D50 illuminant and a CIE 1931 2 degree observer.

As a guide, an error of 1 dE will be noticeable to a critical observer under ideal viewing conditions.
3-4 may be sufficient for non-critical use, while 10+ will be easily discernible to even a non-expert observer.
The DE76 values are for cross reference, the CIE DE2000 values are what count in practice.

Matt measurements: error histogram

    Palette/SwatchMate Cube
        DE76:             worst = 17.9, average = 6.47
        CIE DE2000: worst = 10.5, average = 3.23

    ColorMunki:
          DE76:             worst = 1.77, average = 0.97
        CIE DE2000: worst = 1.35, average = 0.70

Gloss measurement:

    Palette/SwatchMate Cube
        DE76:            worst = 23.6, average = 12.1
        CIE DE2000: worst = 16.2, average = 8.18

    ColorMunki:
          DE76:          worst = 4.52, average = 1.86
        CIE DE2000: worst = 3.96, average = 1.41

Conclusion:

Judging by the unit I purchased, the Palette/SwatchMate Cube accuracy seems to be hit or miss. For some colours it seems to be perfectly usable for non-critical purpose, but with other colours (notably Reds, some Blues, and colours close to Black), it is not so good. A 10 dE2000 error will be quite obvious.

The glossy measurements are spectacularly poor, indicating that it is not suitable for glossy measurement as-is.

Alternatives - ColorMunki Design or Photo

The ColorMunki Design or Photo spectrometer is a much more versatile instrument, capable of strip reading, display and lighting measurement, and of spectral measures such as Colour Rendering Index. As indicated in the above figures and error distribution histogram, its accuracy puts it in a class above the Palette/SwatchMate Cube (in fact the eye-one Pro 2 is probably not quite accurate enough to use as a reference to benchmark it against). It is nearly twice the cost though, but if accuracy is important then you may be better off buying just a ColorMunki, rather than a Cube and then a ColorMunki.

Palette/SwatchMate are to be congratulated on developing and successfully launching an affordable colour measurement device, and also in succeeding in raising the awareness of colour measurement amongst the general public. It's therefore something of a disappointment that the Cube doesn't have an accuracy proportionate to its cost, and consequently there still seems to be room in the market for a competitive low cost instrument, or perhaps for Palette to update the Cube to addresses some of this first models shortcomings.

Reflection: Colour Sensors are easy, instruments are hard:

Sensing the colour of light is cheap and easy - many low cost industrial colour sensors or coloured LED's + a light sensor are available. But emulating how humans see colour is harder - an instrument has to be reasonably faithful in how it emulates the human spectral sensitivities, including the large overlap between the medium and long wavelength sensitive cones, as well as using an appropriate measurement geometry :- when we want to asses a glossy objects colour, we deliberately avoid looking where the specular highlight is, since this gives us no information about its colour composition. Consistently manufacturing a measurement device that has an in-the-field performance equal to the prototypes, also has its challenges.

In Part 2, I see if the application of some Colour Science magic can at all improve the accuracy of the Palette/SwatchMate Cube, as well as make it cope with glossy surfaces somewhat more proficiently.