X-rite 939 illuminate/observer settings

[Polyprintgirl]

We have an X-rite 939 spectrodensitometer that we use with X-rite ColorMaster software.

We were set up with an initial 50/2 illuminate/observer setting (I inherited the color management portion of my job from 2 people that have since left the co.). This I can see in the ColorMaster software. Turns out some of our pressmen are measuring with a 50/10 setting, and saving the L*a*b* values with those settings. I called X-Rite, they said that the 50/2 setting is for printing. They didn't have any specific ideas on what the 50/10 setting might be for, other than that it is a "morning light" setting. I think the pressmen may be using the 50/10 setting by mistake.

If I have the pressmen change to a 50/2 setting, won't they have to re-read all the spot colors they're printing and then re-save them all as 50/2 back into the client list in the ColorMaster software? I thought about going in and changing all their illuminate/observer settings back to 50/2, but I think that'd really screw them up when they went to run the job again.

What exactly does the observer setting do/show? X-rite said that it tells how data relates to the human eye. This is confusing to me.

Any ideas w/b appreciated. Thanks.

[meddington]

Both the Illuminate and observer angle values are used in mathematical calculations to determine the CIELab values. For graphic arts, the default should be D50/2 degree. If your press operators are using D50/10 degree, their Lab values will not correlate to published standards. D50 describes the light source, the spectral power distribution that plot the wavelengths of light along the spectrum. It has a correlated color temperature of 5000 Kelvin (but is actually much more than mere temperature). The 2 degree observer refers to the field of view of the Standard Observer model developed way back in the 1930s. Its essentially the chromatic response of the average human viewing through a 2° angle. The experiments were conducted again at 10 degrees, and hence, that option is available, but again, for the graphic arts, it is assumed that Lab value are derived from D50/2 degree observer.

[Polyprintgirl]

Thanks for the response, meddington! This helps a lot. I've investigated the "standards" list within the software, turns out we're using a mish-mash of 50/2 along with 50/10 settings. I'll let our pressmen know that they need to start using the 50/2 setting for all clients (except one client that uses 65/2.

I suppose they will have to re-read all their spot colors (as they reprint) and re-save with these new illuminate/observer settings, eh?

[meddington]

Just noticed that you are referring to Spot colors. Some in the industry may feel that the wider field of view of the 10 degree observer angle is preferable for spot colors, which are often printed in larger uniform fields. I personally feel that 2 degree should be used in order to have a more meaningful value that can be shared & compared.

[meddington]

I suppose they will have to re-read all their spot colors (as they reprint) and re-save with these new illuminate/observer settings, eh?

Yes, they'd need to remeasure, unless they happen to have the original spectral measurements. This might allow them to recalculate the Lab value with the new observer angle.

[Cornishpastythighs]

CIE standard observer.
Due to the distribution of cones in the eye, the tristimulus values depend on the observer's field of view. To eliminate this variable, the CIE defined the standard (colorimetric) observer. Originally this was taken to be the chromatic response of the average human viewing through a 2° angle, due to the belief that the color-sensitive cones resided within a 2° arc of the fovea. Thus the CIE 1931 Standard Observer is also known as the CIE 1931 2° Standard Observer. A more modern but less-used alternative is the CIE 1964 10° Standard Observer, which is derived from the work of Stiles and Burch, and Speranskaya
Short and sweet explanation

[Polyprintgirl]

Hmmm, interesting about the 10 degree being preferable for spots. Wonder if they got some advice from one of the ink vendors down in TX, although they have their own ink kitchen. The press is remote (Texas), I do the file prep from Denver.

Thanks, all.

[Cornishpastythighs]

We use 10 degree and so does our ink room. Many spot colours so its important we are both using the same. I dont think there is a wrong or right answer as long as you are all using the same.

[meddington]

I dont think there is a wrong or right answer as long as you are all using the same.

Indeed. So long as the illuminate and observer angle are communicated when presenting Lab values, there is no right or wrong method.

[Polyprintgirl]

Makes sense. Thx, Cornish and Meddingtion.