Setting an X-Rite 500 Series SpectroDensitometer to read all densities.
Many printers desire to measure an indication of gray balance using a densitometer. This is possible using any X-Rite 500 Series SpectroDensitometer by setting it to read "Density-All". The present document attempts to provide some background information on how and why a user may want to measure "Density-All" as an indication of gray balance.
The metric of status density is based on reading through three filters: these filters are optimized for reading Cyan, Magenta and Yellow inks. Modern SpectroDensitometers calculate the effective response from these filters through a spectral reading. It is helpful to think of these three filter reading responses as "channels."
Most reflection densitometers use a combination of these three filter readings to measure Black. It is interesting to note that the ANSI standard for measuring black is known as the "Visual Standard," hence the 500 series displays "V" for black readings.
The default setting for the 500 series instrument is "Density-Auto," where the unit automatically selects the "density channel" that yields the highest number: if the user reads a cyan ink patch the unit displays "C" plus the measured density, if the user measure a magenta ink patch the unit displays "M" plus the measured density, and so on. Even though the instrument displays the number representative of the highest density reading, there is still some "signal" in the other channels. When reading process ink solids with an X-Rite 500 series in the default "Density Auto" mode it is helpful to think of the displayed channel here as the primary channel.
To better understand this condition, consider using a densitometer for measuring a spot color green ink: if the green is a "yellow shade" the 500 series densitometer in the default "Auto" mode may display "Y" plus the recorded reading, indicating that to the densitometer, the densitometric channel that yields the most likely response is the yellow channel. If the green is more of a "blue shade," then it is likely that the same instrument would display a "C" plus the recorded reading, indicating that to the densitometer, the densitometric channel that yields the most likely response is the cyan channel. If the shade of the green ink was on the "cusp" of the yellow and cyan channels, that is, if it readings for this particular green yielded a response through the yellow and green channels that were very close to one another, it is possible and indeed likely that the instrument would display a "Y" density reading in some areas and a "C" density reading in other areas. This is because the "signals" of this particular green are very close to one another in the yellow and cyan channels.
Likewise, readings of four color process inks yield signals through each of the density channels, although for readings of solids these signals are not sufficient to produce variation in the channel needed to maintain the ink film thickness for the respective process color, as was the case in the last green example above. Many users have found that the readings obtained through the non-primary channels are useful in maintaining gray balance: to easily access these readings the X-Rite 500 series instruments offer a handy "Density-All" mode. In this mode, the instrument will display any the responses of each of the density channels for each reading.
To set the 500 series instrument to "Density-All," press "x" to go to the main menu, press the "down arrow" until "Density" is highlighted, and press the "enter" key. You will now be in the "Density" mode of the instrument. Now, press the "up arrow" until "Options" is highlighted, and then press the "enter" key. You will now be in the "Density Options" menu, and "Color : Auto" should be highlighted. Press the "enter" key. The "Color" sub-menu will now be displayed, with "Auto" highlighted. Press the "up arrow" and "All" will be highlighted, press the "enter" key to select this mode. You will now be returned to the "Density Options" menu, press the "previous" (middle) key to return to the "Density" mode. When you take a reading, the instrument will display the readings through each of the density channels, with an arrow next to the primary channel.
If you read a three color gray patch, the arrow should be next to the "V" indicating that the instrument thinks that you are reading a black ink, however the numbers obtained from the "C," "M," and "Y" channels should be in balance: typically, within .02 - .03 Density of each other. Astute press professionals will soon notice that this indication of balance correlates strongly to a visual assessment of the three color gray patch. If cyan, magenta and yellow ink films increase or decrease at the same time and rate, gray balance is typically maintained and customers perceive less color variation. As an example, if a user were to measure a three color gray patch and notice that one of the process colors is .05 density higher than the others, a noticeable shift in the neutrality of this tint is indicated. This shift will cause an objectionable and noticeable color cast on many process color images and therefore requires a press adjustment.
©Copyright Bruce Leigh Myers, Ph.D. July 19, 2008