Computing the visual density from RGB readings

Hello,

does anybody know, how to transform the status M color negative density readings from a color densitometer to a visual density value?

As I understood, my X-rite 310 does not measure the vis. dens. but computes it from the measured RGB densties. I would like to do this computing myself to controll the densitometer.

Thanks a lot!
Gerhard

Good question but really I don't know the answer. If the RGB values are equal then the vis. density is the same. If they are not the same it seems that the G density has more weight in computing the vis. density.

Some time ago, somebody told me, that the RGB values are weighted R 30%, G 59%, B 11% to get the Vis density. You first have to delogaritmise the values, weight them acording to the percentages above, devide the resulting value by 3 and then relogaritmise it again. My problem is, that I get a diffrent result as the X-rite 310, when I measure color negative in status M. Are the percentages wrong or did I make a fault while computing them?

Thanks
Gerhard