How to assess the color performance Raiders (below)

How to make a reasonable evaluation of the accuracy of color?

We know that the accuracy of color is obtained by comparison, so we must first take some standard colors as a reference before evaluating. However, the standard colors are as difficult to find as the standard beauty. For this reason, we have found two KODAK standard swatches (the two humble little pieces of paper can cost several hundred dollars!). Through the paper, we can Accurately distinguish between "green and white soap." Below we discuss how to use this standard swatch to evaluate color printers.

As we mentioned earlier, the four-color ink cartridges used in general printers correspond to the four components in the CMYK model, while the colors of other prints are made up of these four colors and thus the four kinds of printers are accurate. To a large extent, sex determines the accuracy of the overall color output. In addition, three colors of RGB can be obtained through the CMY three-color combination, and CMYRGB corresponds to the six basic colors of the standard color palette. We see that there are six kinds of lighter colors on the standard color swatches. In fact, they correspond to reducing all ink consumption by half to form lighter colors. The following are the parameters of each color of the standard swatches in the CMYK model. List:

Through Photoshop software, we can easily use the computer to imitate a standard swatch. At this time, let the evaluation printer output this "defective product". By comparing with the genuine product, we can know the accuracy of the color output.

The above picture is a comparison of HP 8158 manufacturing counterfeits and genuine products. We can directly see that 8158 has a large error on the blue output, while the red error is relatively small. Some people here may protest. - "You say that the error is big and small all day long. What exactly is the size of the big one?" Yes, "size" is indeed a vague concept, so we should try to quantify this error.

Since we do not have a professional instrument to measure the error of the two colors, all of them only rely on Photoshop software once again. We first open the photo of the "sham product" and the genuine product with Photoshop. Press F8 to see the information window as shown above. At this point, we can use the mouse to point to the color part of the picture. This color will appear in the window in the corresponding color model. The next value. Again, we chose the hue attribute of the HSB model to measure the accuracy of the color, because this photo is taken by a digital camera, and the difference between the printed paper used will cause a large error in the color saturation and brightness, but We can think about singers singing. If singers use octaves or octaves, they won't sound very hard to hear, but if you sing out and tune up, everyone will feel very uncomfortable, so this “tone” is a One of the important parameters. The following is the analysis data of the above photo:

From the analysis results, the hue error is very similar to the error we see directly with the eyes. As the above measured data knows that there is almost 10% error between blue and light green, and we take a closer look. "You will find that the difference between these two colors is indeed quite large, which means that the machine has a certain lack of accuracy in the output of blue and light green.

In addition, we see that there is a gray standard swatch, the same method can be used to measure the accuracy of the machine in terms of grayscale printing, but generally we only use it to see whether the output of each level of gray printer is obvious Some low-grade printouts often fail to recognize the boundaries of the highest two levels of grayscale.

Obviously, the above is the introduction of color evaluation is still limited, it can only assess the error of several colors, and the evaluation workload is also relatively large, lack of relevant knowledge may feel incomprehensible, so I am here Introduce another kind of comparatively simple color accuracy evaluation method --- the color tape compares the law.

We use Photoshop's discoloration tool to make a bar with all the base tones, as shown above. After the output of the printer under test is used, it is scanned into the computer with a better scanner, and compared with the original image, the accuracy of the color output of the product can be approximately known.

Of course, this method will be affected by the color accuracy of the scanner, but in fact the accuracy of the color of the general scanner is much higher than the printer, and this method can also see the printer output color range, which is the former Evaluation can not be done.

As for the scanner scanning color evaluation method, in fact, with the digital camera evaluation is similar, because the scanner driver is generally with automatic adjustment of the color balance function, as long as the standard swatches with a scanner into the computer after the original The map can be compared directly, if necessary, you can use the tone comparison method described earlier to test.

Reprinted from: China Inkjet Forum