So, you think your grey card is grey?

Hi all,

I have been playing with my colorimeter today.

Since I have a few grey cards, which have served as a “standard” for processing during the years, I thought it would be of interest to see how “grey” they really are. Here are the results, expressed in sRGB:

Lastolite	 97,  98,  99
SpyderCube	111, 111, 108
Colorchecker	200, 200, 199
Electra  	173, 175, 175
QP-card 	108, 109, 110
Colour Conf.	108, 110, 111

Have fun!
Claes in Lund, Sweden

3 Likes

Can the colorimeter output XYZ or Lab? I’d be interested in those raw numbers.

Moin, houz!

The colorimeter I have is an X-rite ColorMunki Photo. The software that comes with the gadget only works under Windows and presents its readings as Lab, HTML and sRGB.

In Linux I have ArgyllCMS installed. Using spotread -s I will get readings as D50 Lab as well as XYZ.

I just made a quick comparison, using Colour Confidence’s grey “mat”:

> 170925
> ColorMunki Photo
> X-rite	Lab
> Colour Conf.	48.2 -0.7 -1
> 
> spotread -s	D50 Lab				XYZ
> Colour Conf.	48.102196 -0.727729 -1.098454	16.142734 16.875038 14.339505

Which of these two methods (Win or Linux) would you like? Or would you prefer that I install a third pgm?

MfG
Claes in Lund, Schweden

spotread should be fine. And only if it’s not too much of a hassle. It’s mostly for educational purpose. :slight_smile:

Abends!

170925
My GreyCards
Colorimeter	ColorMunki Photo
argyll spotread	XYZ				D50 Lab
Lastolite grey	11.883609 12.378776 10.433273	41.811898 -0.362705 -0.717014
Lastolite white	71.784110 74.955923 60.891158	89.372344 -1.025849 0.925740
SpyderCube	14.798524 15.386060 12.124309	46.158491 -0.221475 1.622392
Colorchecker	55.250960 57.362917 46.890109	80.383287 -0.146598 0.503570
Electra		41.060441 42.797249 35.984637	71.417142 -0.624354 -0.962885
QP-card		14.075054 14.684919 12.368800	45.199589 -0.523849 -0.735636
Colour Conf.	16.276820 17.007448 14.495050	48.269419 -0.687624 -1.212278

OK?

Have fun!
Claes in Lund, Schweden

1 Like

Can I infer from the data that your Colorchecker is the greyest?

Morning!

The Colorchecker is the most neutral of them.

Have fun!
Claes in Lund, Sweden

I can confirm that:

Name             L          a          b           deltaE (neutral)  deltaE (50%)

Lastolite grey   41.811898  -0.362705  -0.717014   0.80              8.23
Lastolite white  89.372344  -1.025849   0.92574    1.38             39.4
SpyderCube       46.158491  -0.221475   1.622392   1.64              4.18
Colorchecker     80.383287  -0.146598   0.50357    0.52             30.39
Electra          71.417142  -0.624354  -0.962885   1.15             21.45
QP-card          45.199589  -0.523849  -0.735636   0.90              4.88
Colour Conf.     48.269419  -0.687624  -1.212278   1.39              2.22

The comparison colour was derived from the measurement by simply setting the a and b channels to 0.0 while keeping the L. The usual interpretation of deltaE is that everything below 2.0 looks the same to the human eye, so while those might not be good enough for scientific measurements I wouldn’t worry too much for actual use. In case someone wants to play with that you can find the libreoffice spread sheet here, zipped to please the forum software:

None of them are really neutral 50% Lab though.

greycard_deltaE.zip (9.8 KB)

Edit: deltaE against 50% grey added.

2 Likes

Now it begs the question: is the Colorchecker the most neutral because you kept it the cleanest of all your grey cards? :owl:

You mean my dirt has a colour cast? :worried:
Actually, I do not think so, since almost all of the cards
are kept in a nice drawer and they are not handled
more than when in use.

/Claes

@Claes I guess the material, construction, condition and age would have an impact too. Also, not all targets are made equal. Personally, I am not serious enough to use a target :blush: but I am sure this thread would be instructive for many.

@houz I don’t know much about deltaEs. How should I read the two columns?

My old Mennon grey card gives somewhat different values depending from which part of the card the measurement is taken. It has been used a lot and got dirty. Eventually it started to give consistently too high color temperature with tint trending too high on the green side, and therefore I replaced it with Spyder Cube. I was told in a camera store that UV radiation can damage grey cards if they are used a lot outdoors (as I have done).

I am rather happy with my Spyder Cube. Paid 19 euros for it (normal price here in Finland is 59+ euros… ridiculous!). It fits in pocket. You can get two grey card readings with single shot if necessary: one for lit part, one for shadows. White and black sections are more or less useless, but the reflective part is perfectly usable for self-portraits… :smiley:

1 Like

delta E is basically the distance between two colors in Lab space. If it is less than 2 the two colors are considered to be indistinguishable by the human eye. Of course it’s not a scientific fixed truth but a rule of thumb, so some people might be able to tell colors apart that have delta E of 1.5, some might not see a difference of 5. The column “deltaE (neutral)” has the difference between the measured Lab color and the grey with the same L value. For example, the Lastolite grey card measured as L = 41.811898, a = -0.362705 and b = -0.717014. Comparing that to L = 41.811898, a = 0.0 and b = 0.0 gives a delta E of 0.8 which is darn close and therefore the color tint is not something anyone would see.

The column “deltaE (50%)” is comparing all grey cards to the same 50% grey Lab color. It’s not very useful to do that as the cards are probably not meant to be neutral grey in the first place, but it might be interesting to see how far they are off.

The Wikipedia page has more about the theory. I used the 1976 model btw.

1 Like