Tolerance for Black to G7

[Bill W]

Greetings,

I have created a zipped Excel file (see attached) that will calculate C, H and dE (CMC2:1) to G7 based on the readings from my 528. I use this file when setting up our flexo presses, as I have found it is more accurate to average 3 consecutive readings.

My challenge is with black. I am not a math whiz. A friend sent me an Excel file with the formulas, and I just re-linked them with the cells in my file that are filled in from my 528 readings. Since the black has no C or H, the formula to report tolerance falls apart.

Is there someone out there that would be willing to send me an Excel file that has a formula that will work for black, or tell me how to adjust the formula to work for black.

Thanks.

-Bill-

 

[meddington]

Greetings,

I have created a zipped Excel file (see attached) that will calculate C, H and dE (CMC2:1) to G7 based on the readings from my 528. I use this file when setting up our flexo presses, as I have found it is more accurate to average 3 consecutive readings.

My challenge is with black. I am not a math whiz. A friend sent me an Excel file with the formulas, and I just re-linked them with the cells in my file that are filled in from my 528 readings. Since the black has no C or H, the formula to report tolerance falls apart.

Is there someone out there that would be willing to send me an Excel file that has a formula that will work for black, or tell me how to adjust the formula to work for black.

Thanks.

-Bill-

You could try this one for comparison: http://www.digitalcolour.org/Difference.zip

There are a number of differences in how the spreadsheets are put together, but hard to pin point unless you adept to mathematical thought. Off hand i'd say its odd that your spreadsheet shows a h value of 180 with zero a* & b*.

 

[Bill W]

Greetings Michael,

Thanks, as always for your interest. I do have the Excel file you referenced, and while the formula in that file does not compute the hue for black (whereas mine returns 180°), it also cannot compute a tolerance number.

Bruce Linbloom's website does compute a tolerance for comparing a black to the G7 black values and also computes both C and H for black to be 0. There are formulas on his site, however my math education stopped at intermediate algebra and geometry, and even reading the definitions of cos and tan kinda of makes my head hurt.

-Bill-

 

[meddington]

I do have the Excel file you referenced, and while the formula in that file does not compute the hue for black (whereas mine returns 180°), it also cannot compute a tolerance number.-Bill-

Hmmm, not sure what you mean. This spreadsheet appears to work fine here.

I'll take a look at your spreadsheet more closely when I have a chance. I'm thinking there are just a few simple errors that make the difference.

 

[Bill W]

In the Excel file I downloaded from you link, on the CMC page, I have placed L=16, a=0 and b=0 in the reference and then L=18, a=0 and b=0. My results, which show no H or tolerance being calculated, are the attached screen shot.

Are your results different?

-Bill-

 

[meddington]

weird. no problem on my end.

 

[Bill W]

In the Excel file I downloaded from you link, on the CMC page, I have placed L=16, a=0 and b=0 in the reference and then L=18, a=0 and b=0. My results, which show no H or tolerance being calculated, are the attached screen shot.

Are your results different?

-Bill-

 

[Bill W]

Dare I ask, are you on a PC or a MAC. I am on a MAC running Excel X for Mac and I have heard there are some differences - maybe this is one of them.

-Bill-

 

[meddington]

Mac, but using OpenOffice. I just tried on a PC in Excel (03) and lo and behold, it don't work. Can't divide by zero. Maybe you could finagle this into it: HOW TO: Suppress #DIV/0! Error Value in Division in Excel 2000