Posted by Elaine Becker on Thu, Apr 08, 2010
This blog article was written by Dr. John W. Root of Mt. Baker Research:
A translucent solid is not perfectly opaque. Part of the light incident on it penetrates the surface where it undergoes internal scattering and lateral diffusion away from the entry point. Both processes reduce the intensity of reflected light.
Because of lateral diffusion, the reflectivity of a translucent solid decreases as the size of the instrument's sample port is reduced. This effect causes systematic errors in measured spectral reflectance factor ("SRF") data. The magnitude of these errors depends on the following: (1) Instrument geometry. (2) Characteristics of sample surface. (3) Sizes of illuminated and measured areas of sample.
Measurement of Translucency
In commercial spectrophotometers that support diffuse illumination, the entire exposed surface of the sample is illuminated and an optical system controls the area viewed by the detector. Over-illumination is achieved by configuring the viewed area to be smaller than the illuminated area. Experiments in which over-illumination is varied can be used to measure the fractional reflectance losses ("FRL") that result from lateral diffusion. The author recently used this technique to measure FRL values for many ceramic tiles, glasses, and plastics.
The X-Rite ColorEye 7000A ("CE7000A") spectrophotometer supports a wide range of over-illumination. Maximum over-illumination is achieved with the LAV/VSAV configuration in which the LAV sample port is combined with the VSAV lens setting. The VSAV/VSAV configuration minimizes over-illumination.
The typical FRL results reported below were calculated from SRF data measured using the LAV/VSAV and VSAV/VSAV configurations of a recently purchased CE7000A (S/N 37132651108). The success of this method requires that the instrument's white calibration tile exhibit negligible translucency. This was the case for the author's new CE7000A, but not for his 2nd instrument (S/N 37116190602).
Translucency in Transfer Standards
The author's tests demonstrated that many optical materials exhibit translucency. For the FRL values listed below the 2σ standard error of estimate is ± 0.03%.
Typical Values: White Carrera® glass, 25.6%. Extruded Teflon®, 22.9%. White Vitrolite® glass, 18.9%. Ceram red-orange 99/1 tile, 8.98%. Sintered PTFE powder (Fluorilon® and Spectralon®), 3.6% - 2.9%. Ceram red tile, 3.14%. MC-20 Russian white opal glass, 3.13%. Ceram orange tile, 3.03%. Ceram yellow tile, 2.52%. X-Rite white calibration tile (S/N 37116190602), 1.43%. Konica-Minolta CMA103 white tile (S/N 18776042), 0.90%. X-Rite white calibration tile (S/N 37132651108), 0.00%.
Although FRL values may be measured using other instruments, the results will depend on the translucency of the instrument's white calibration tile as well as the dimensions of its LAV and VSAV sample ports.
Comparisons of SRF data measured using instruments with large vs. very small sample ports should be based on opaque transfer standards. If the standards are translucent, inter-instrument agreement cannot be achieved. Instrument profiling cannot mitigate the errors that result from the following sample characteristics: (1) Thermochromism. (2) Translucency. (3) Surface inhomogeneity.
The guidelines listed below are based on the sample port sizes of the CE7000A. They are recommended for transfer standards that are used for testing and profiling instruments in the diffuse SCI geometry. The FRL values should be less than 3.5% for instruments that support over-illumination and a LAV, MAV or SAV sample port. For instruments that support a VSAV sample port, the values should not exceed 1.5%.
The author of this article is John W. Root Ph.D. of Mt. Baker Research who can be reached via email at jackroot@mtbakerresearch.com.
Posted by Elaine Becker on Tue, Jan 05, 2010
Long before computers were invented a radio, film, and television comedy team known as Abbott and Costello perfected a classic skit that became known as the "Who's on First?" routine; essentially a dizzying five-minute display detailing by example the pitfalls of miscommunication via homophones, homonyms, home-run hitters, and high comedic art.
Not so funny is the frustration and confusion many working in color measurement experience due to the persistent misuse of terminology. "Why don't my color numbers match?" is a question we hear often.
The Many Angles of Color Measurement
Probably the most common misconception is about the 2° and the 10° observer. This frequently gets mixed up with the geometry of the measuring instrument with users saying they measured the color at 10° using D65 illumination, when in fact what they measured the sample with was a 45° /0° instrument using tungsten illumination. The 10° comes into play with the Standard Observer they chose for the tristimulus weighting functions.
There are two areas where these angles come into play and it's easy to see how they can become confused:
The first is the instrument geometry and how the light source and detector are positioned relative to the sample.
- The second is less obvious and goes back to how the tristimulus weighting functions are specified.
The 45°/0° refers to the geometry or optical design of the measuring instrument, be it a colorimeter or a spectrophotometer.
The most common instrument geometries used today are either 45°/0° or d/8°.
The instrument geometry is described by a pair of angles or letters. The first letter or number in the pair is for the angle of illumination; the second is for the viewing angle (or the angle that the light is detected).
So, for 45°/0°, the sample is illuminated at 45° off the normal (perpendicular to the sample) and the reflected light is viewed or detected at 0° (meaning perpendicular to the sample).
In the second example of d/8°, the ‘d' stands for diffuse illumination, meaning the sample is illuminated at all angles by diffuse light coming from the integrating sphere. (The integrating sphere is the white-coated ball collecting and diffusing the light).
The second term in d/8° stands for the angle of viewing which is 8° off the normal.
Angling for better color management
So, what are the 10° and the 2° all about?
This seems to be where all the confusion is centered. These angles refer to the Standard Observer and have nothing to do with the geometry of the instrument or the angle at which the samples are viewed.
Instead, the 10° and the 2° angles refer to the field of view when physically viewing a sample. The field of view subtends either a 2° or a 10° angle on the retina.
A better way to understand this is that a 2° field of view is equivalent to viewing a 1.7cm circle at a distance of 50cm; a 10° field of view is equivalent to viewing an 8.8cm circle at a distance of 50cm.
So roughly, the 2° field of view is equivalent to viewing a 1.7cm circle at a distance of 50cm; or like looking at your thumbnail at arms length away and the 10° field of view is like looking at the palm of your hand (or a three-inch circle) at arms' length.
The color of consistency
In industrial color control, the 10° Standard Observer is recommended because it more closely approximates the size of samples being evaluated, but you'll still find lots of standards and procedures using the 2° Observer.
These terms are important when trying to communicate color up and down the supply chain. Being able to communicate precisely how the numbers were determined is key to someone else being able to reproduce them accurately.
And now, if someday you're out at the ballpark and someone asks you, "Who's on first?" you'll know to just tell them, "Yes," and let it go at that.
Posted by Elaine Becker on Mon, Dec 07, 2009
If we put you under the spectrophotometer now, would you show up in deep shades of recession blue? Perhaps.
Tough economic times often mean having to make do with fewer resources to handle the workload. The same workload for developing new colors, adjusting production batches, and approving colors is spread over fewer people. Staff become stressed and can easily overlook color shifts they might otherwise have caught.
And, as you know, color shifts take time to correct. They result in product that either has to be reprocessed or worse, discarded, let alone the time and labor required to make the corrections.
Sometimes, it's the more experienced staff-the more expensive staff-that had to be let go, and along with them, went years of knowledge of how to work the color matching system or operate older, more finicky equipment.
But, just like a painter who switches from brush to roller and roller to spray gun, an investment in the right industrial color matching or color quality control technology can help ease the burden while increasing productivity and reducing costs.
Don't paint yourself into a corner
Investing in technology is one way to keep up with demand while keeping payrolls lean.
Consider these advantages from a new, up-to-date, industrial color matching system:
Fewer production adjustments: The software can automatically calculate and add colorant to bring production back on track.
- Optimized adds: Color matching software can find the one, optimal colorant to add to correct a batch.
- Batch size variation adjustments: Color quality control software automatically calculates accurate adjustments by weight or volume, or even when the batch amounts are not known.
- Faster estimating: Detailed production costing lets you provide estimates faster, beating the competition to the bid.
- Wider color range: Today's sophisticated industrial color matching software databases help you reduce the number of colorants in inventory while broadening the range of colors you can produce.
This recession will end someday (or so they keep telling us). In the meantime, consider how technology can increase productivity, lower inventory, and keep staffing costs in check. Then, focus on the future, one with a bright, sunny, yellow outlook.
Posted by Tom Merck on Wed, Sep 02, 2009
Many color instruments and spectrophotometers in use today come with a serial cable to connect and communicate with a computer. However, serial ports are a thing of the past and very few PC's come with a serial port as standard 
configuration these days. While you can always install a serial port, an easier way to connect to the PC is to use a Serial to USB adapter. This is a special cable that plugs into the serial port output of your spectrophotometer on one end and plugs into a USB port on the computer on the other. This circumvents the need for a serial port on the PC.
There are a few tricks to getting this to work however. Resist the temptation to just plug the cable in and see if it works!!! First, it is important that you read and follow the installation instructions that come with the USB adapter. Typically (but not always), the instructions will direct you install a driver for the adapter BEFORE plugging it into the computer. It's important that you follow the proper sequence, because once you get Windows confused on what is attached to this port, it can be difficult to undo it.
After installing the driver, go to the Windows Device Manager and go to Ports and note what COMM PORT the adapter was assigned to. I In Windows Xp Device Manager is found under Control Panel, then System, then Hardware tab, and then Device Manager button.) You will need to know this in OnColor when you tell it what Comm. Port to look for the spectro on. Then connect the spectrophotometer to the adapter and finally plug it into the PC.
For spectrophotometers that do not use a "straight through" cable, you will need to use the manufacturer's cable out of the spectro and then attach the USB adapter to the 9-pin end of that cable. (Examples of spectros like this would include the Konica Minolta CM-3600d, CM-2600/2500d and CM-3700d.)
Finally, you can open OnColor and go to Communications, choose the comm. Port assigned to this adapter and then test the settings. You should be good to go.
Don't move the adapter around to different USB ports, as the driver typically only configures it for that one USB port. If you move it to another USB port, it may be assigned to a different comm. Port number.
Not all USB adapters are created equal. Some are not compatible with Windows Vista. Others don't handle this type of data communication well. We recommend the Belkin serial to USB adapter (http://belkin.com/support/product/?lid=en&pid=F5U257&scid=1 ) since many OnColor users report no problems using this model.