• Welcome to Photrio!
    Registration is fast and free. Join today to unlock search, see fewer ads, and access all forum features.
    Click here to sign up

Question regarding color densitometer.

Chan Tran

Subscriber
Allowing Ads
Joined
May 10, 2006
Messages
7,191
Location
Sachse, TX
Format
35mm
I have a question regarding color densitometer whether reflection or transmission type. I know all of them only have 3 sensors and only measure the R,G and B. They use the RGB value to compute the V value. I wonder is there a formula to do that? I know if the reading is 1.00, 1.00, 1.00 on all 3 color channels then the V is also 1.00 but what if the RGB values are different? Just and average of the 3 or is there a weight for some channels.
 
None of my color densitometers work that way. Is there a specific unit you know of that works that way?
 
The luminosity method is a more sophisticated version of the average method. It also averages the values, but it forms a weighted average to account for human perception. We’re more sensitive to green than other colors, so green is weighted most heavily. The formula for luminosity is 0.21 R + 0.71 G + 0.07 B
 
I think that Prof_Pixel is describing the weighting used in a television standard (Rec.709), which I think is only valid for a specific set of phosphors and a certain visual adaptation (ie, to a specified color temperature).

I don't think it's legitimate to use this for densitometry; they're just different things.

The ideal thing is to use a densitometer with a proper visual response. I don't believe it is possible to derive the visual density of an arbitrary material from standard tri-color densities (Status A or Status M).
 
What I am asking is my densitometer like most has 4 readings R, G, B and V but it only uses 3 channel sensor. How did it figure out the V.
 
Chan Tran said:
What I am asking is my densitometer like most has 4 readings R, G, B and V but it only uses 3 channel sensor. How did it figure out the V.
Click to expand...

What brand of densitometer is it. I have not seen a densitometer that shows "V". You probably need to contact the manufacturer to find out.
If "V" is from the HSV system, then there are some converters on-line that can go from RGB to HSV: http://www.cs.rit.edu/~ncs/color/t_convert.html#RGB to HSV & HSV to RGB http://www.javascripter.net/faq/rgb2hsv.htm

The color densitometry chapter in Todd an Zakia describes Equivalent Neutral Density (END) and mentions that if you know the END and Analytic Spectral Density of a dye, you can take that ratio and use it in the ASD/ISD conversion matrix to calculate END.
 

The densitometer is the X-Rite 810 reflection/transmission densitometer. The V stands for Visual and it's the same as B&W density.
 
Chan Tran said:
The densitometer is the X-Rite 810 reflection/transmission densitometer. The V stands for Visual and it's the same as B&W density.
Click to expand...

Why do you think it calculates the "Visual"? From the manual, it would seem it measures it at the time it measures the 3 colors. Perhaps you have had the measuring head off and saw 3 sensors only?
Also, common sense indicates the "X-rite Visual" may be similar to a B&W density reading, but did you see in any documentation that it is indeed "the same as B&W density?"
Each time a measurement is taken, all four colors (visual, red, green, and blue) are read
Click to expand...

Anyway, the "X-rite Visual" has my curiosity because my x-rite 890 does not display the "X-rite Visual" output, it just lists the 3 colors. Also, this X-rite document on color standards and measurement does not mention "Visual" or "X-rite Visual": http://www.xrite.com/documents/literature/en/L10-001_Understand_Color_en.pdf
 
Last edited by a moderator:
You must log in or register to reply here.
Menu
Log in
Register