How to measure color difference

how to measure color difference

In-Depth Guide on How to Measure Color in Plastics

Feb 09,  · By comparing measurements of target colors with sample specimens, the user obtains not only a numerical description of a color, but can also express the nature of a color difference between two measured specimens. The colorimeter pinpoints the difference in lightness, chromaticity, and hue between the target and the sample. Delta L (? L) Lightness/darkness differences + = lighter than, – = darker than. Delta a (? a) Red/green difference + = color is redder than, – = color is greener than. Delta b (? b) Yellow/blue difference + = color is yellower than, – = color is bluer than. Delta c (? c) Chroma or saturation differences + = more chroma, – = less chroma.

Metal How to adjust boat lift bunks Tanks. Photo courtesy of Altana. Metallic colof can be difficult to quantify for color.

The color measurement varies dramatically with the angle that you view it. It measures the color and sparkle of the metal and other effect surfaces at 6 different angles and even quantifies how much sparkle there is on the surface. However, this is just too much information for basic color quantification of bare metals, building materials or inexpensive household or automotive accessories.

These could be shiny objects such as door knobs, chrome decals, brass kick plates, etc. But could also be steel girders or low sheen stainless steel furniture trim. The manufacturer just wants to know that the metal surface is similar in color to the last set of door knobs or kick plates that he turned out.

Often this is used to ensure that the quality of the metal is equal to ddifference last batch. The right combination of metals to make an alloy will produce a product with a similar color and gloss. The wrong combination will not only result in a different colorbut could also mean some loss in other physical properties rust resistance, scratch resistance. BYK-Gardner spectro-guide.

Photo courtesy of BYK-Gardner. Color varies on metal when you view it from different angles. The spectro-guide Sphere, however, measures all of the light that reflects off of the surface.

How to measure color difference one caveat to using the spectro-guide for measuring the color of metals is that the gloss measurement will not be completely accurate. The gloss meter built into the spectro-guide does not include the metallic range found in the micro-gloss meters sold by BYK-Gardner. These metallic ranges are really necessary for metal surface evaluation. Otherwise every sample will read about the same gloss : GU at the top of the range.

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Color and Appearance Concepts Explored

If we put the values of ?L*=+, ?a*=, and ?b*=+ into the color difference equation, it can be determined that the total color difference between the two apples is = [^2 + ^2 + ^2] ^1/2. Identifying Color Differences Using CIE L*C*H* CoordinatesEstimated Reading Time: 3 mins. Color measurement usually works by analyzing a subject object and comparing it to a known color sample. The color samples are used because they have known, and documented, color euro-caspian.comted Reading Time: 6 mins. Color in Isocyanates,” provides a test method for measuring the color of clear, yellowish liquids. ASTM D, “Standard Test Method for Evaluation of Color for Thermoplastic Traffic Marking Materials,” describes using a 45°/0° colorimeter or spectrophotometer to measure these.

In the plastics industry, standardizing the color process can be both difficult to understand and even harder to implement. Here are basic tips for improving color measurement and establishing color consistency.

It is no secret that Standardizing the Color Process improves manufacturing operations, especially when it comes to plastics. From batch to batch or plant to plant , it is imperative that the final product matches the design and each other. The only way to control your plastics color consistency is to measure it, accurately. It is critical for QA managers, manufacturers, engineers, chemists, and technicians alike to all understand the basics of all color measurement.

Without knowledge of the fundamentals, it will be difficult to understand what is needed for precise measurement and will be very difficult to communicate those needs throughout your supply chain.

Here are a few to consider first:. If you feel that you and your team have a solid understanding of the basics, then the next step in your standardization process is to choose your evaluation conditions.

Starting with:. Remember, precise color measurement instrumentation and sophisticated formulation software are required to avoid expensive trial and error periods and get the color correct the first time. Spectrophotometers are quality control devices that provide numerical values for color. Benchtop spectrophotometers are the tool of choice for blown, extruded and molded plastic products.

Use a spectrophotometer to store the product color code. If changes in production at a future time alter the color, the original color can be re-instituted. Unlike a light source, an illuminant can be represented by the light's spectral power distribution curve in graph or numerical form as depicted here. Without light, we cannot see color.

With light, color appearance changes from one type of light than another. An apple, for example, could appear redder under incandescent lighting than it does under natural daylight. This often leads to inconsistencies in evaluating or communicating the color of a sample.

Standardizing lighting conditions maintains consistent results for each evaluation. Standard Illuminant D Average daylight including ultraviolet wavelength region with a correlated color temperature of K. Standard Illuminant A: Incandescent light with a correlated color temperature of K. Once you know how to illuminate your plastic, you need to standardize your perspective. An object may appear brighter, duller, lighter, or darker due to light reflection. It all depends on the observer's angle relative to the object.

Test and control an object's color using a standardized method. Remember, light must reflect off the object at the same angles during each assessment. Color measurement instruments, including spectrophotometers and colorimeters, illuminate an object at certain angles to detect its color. Color measurement instruments including spectrophotometers and colorimeters illuminate objects to detect their color.

The instrument's optical system geometry detects an object's illumination angle and reflection angle. That geometry effects where an object's color falls in the defined color space. Different measurements can result from instruments with other geometries. Identify ideal geometries for plastic color evaluation and control by reading common geometries built within color measurement instruments.

A "color space" is a method for expressing the color of an object using some kind of notation such as numbers. Use defined color spaces for evaluating color attributes, identifying inconsistencies, and expressing findings. Color measurement instruments make quantifying these color attributes easy.

Even if two colors look the same to you , color measurement instruments could show slight differences. Slight differences can also be the difference between a happy and unhappy customer or client. Color samples that deviate from the standard compromise customer satisfaction.

These non-uniform samples also increase the amount of rework and costs. Achieving the desired product color with an efficient and streamlined process is the goal of every color quality process. Ensure consistency and accuracy throughout your quality process by establishing color tolerances.

A color tolerance is the acceptable difference in color between a sample and the standard. For color to be acceptable, your color tolerance values should always correlate to the human eye.

The CMC tolerance system uses ellipsoids based on the color discrimination threshold of the human eye. The DE00 color difference formula recommended for plastics incorporates ellipsoids plus the hue angle. Measurement of color samples requires standardized procedures. Standardize the preparation and presentation of your samples for each reading. Errors and inconsistencies between samples and standards occur without standardized methods.

Listed below are preparation and presentation best practices to achieve more accurate and consistent results when measuring the color of your samples. The method for evaluating the color and appearance of a sample is unique to each application. Many applications including plastics need visual assessments along with instrument measurements. Conduct visual assessments for inconsistencies between the sample color and the standard color.

Before commencing a visual assessment, condition the samples, if needed, prepare and present the same each time. That means grinding, mixing, or slicing samples the same way. Place the samples in the same container, and use the same sample quantity or size for each assessment. To maintain consistency and accuracy requires standard conditions.

This includes standards for lighting, observer, and viewing conditions. Try to use the same color recipe as your standard when formulating the color of your plastic product. If this is not possible which is often the case , then define a color formulation process and create a recipe that matches the original's standard.

To learn more about Konica Minolta and resources for color consistency, click here. Find a Supplier to the Plastics Industry. Get PT in Your Inbox. Next up X. Fetching next article.

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