Talking about the test method of the color reproduction ability of the scanner
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Most scanners are calibrated at the factory, but due to differences in manufacturing conditions, changes in the color temperature of the source, age, etc., can affect the scanner's hands. When purchasing a flatbed scanner, the manufacturer generally provides a standard transmissive or reflective original that includes a neutral gray scale and partial color patches. After normal scanning of the standard original, observe a certain line image in the image in Photoshop 6.0 (observe the white line or the black line is particularly obvious) whether the RGB three-channel pixels overlap, so as to check the scanning accuracy (the magnification should be selected at the time of observation) ). The corresponding pixels of the RGB channel do not coincide, which on the one hand will affect the sharpness of the scanned image, and on the other hand, affect the color reproduction effect during the copying process.
The neutral gray scale ruler was used to test the ability of the flatbed scanner to restore the neutral gray color and the performance of the ladder density level. The correct restoration of neutral gray color by the scanner is the premise and basis for identifying color and reducing color. Scanning color cast is caused by the difference in color perception performance of the scanned components from the standard components during the scanning process. Although the device has been calibrated before leaving the factory, there are inevitably some color casts in use. In the actual process, the display screen is often corrected so that it can display the color correctly, and then correct the scanning color cast.
At present, the pre-press production center uses a medium-to-high file scanner, and most of the software can customize the output characteristic file. For example, the Heidelberg scanning software NewColor can define the culture of RGB output characteristics. Just set the output property file in the scanning software to match the "RGB setting" in PhotoShop, so that the image in PhotoShop is almost the same as the screen display in NewColor. For scanners with a lower file size, scanning profile files are not supported and PhotoShop features can be used.
When correcting the scan color cast, the scanned neutral gray scale is placed in Photoshop6.0 image processing software, and the information palette is used to display the RGB values of the scales in the image, and the Curves curve is called to adjust the RGB three channels. Until the CMYK display value of each step in the image reaches the required value in neutral gray, and the visual neutral gray scale can be visually observed on the display screen. The Curves curve at this time is the color curve after the scanner corrects the color cast. When scanning the image, the scanned color should be properly compensated according to the curve, and the curve can be saved for calling. By scanning with color patches in a standard original, it is possible to judge the reproduction characteristics of the scanner for each color. The visual contrast between the original color patch and the scanned image can qualitatively recognize which colors the scanner reproduces better and which colors are different, so that in the future, in the scanned image, the color with poor reproducibility is corrected by the image processing software. In addition, the scanner should be calibrated regularly.