Print knowledge summary 8A
Problems to be aware of before outputting files
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One. about scan separation
The scanner calibration principle is to adjust the scanner to be able to faithfully copy the original's tone level information, color change, and gray balance. The specific method is to use a dedicated emission or transmission color scale to adjust the gamma values of the highlights, shadows, and intermediate values in the scanning software. Adjust RGB or CMYK single-channel values as necessary to make the electronic image's tone, color, gray balance, and color scale consistent. The steps are as follows:
1. After the scanner is turned on for more than ten minutes, the standard color mark is placed in the scanning area, and the scanning software is started to scan with the default parameters.
2. After the scan is complete, measure the grayscale color data with a probe in Photoshop. According to needs, the highlight value and the dark tone value are adjusted in the scanning software so that the first level of the gray scale is between 250 and 255 and the dark level is between 0 and 5 in the 22nd level. If the value of the dark tone after the scan is large, it means that the dark tone is not black enough. You can increase the value of the shadow tone from 0 to a larger value to ensure that the 22nd level value is comparable to 5 or less. Of course, the calibration of the white field is also the same. Between the 19th and the 22nd level, the values are not much different, roughly 10 or so, the dark tone level has not been opened, and the tone is compressed and lost. This is determined by the performance of the scanner itself and has little effect on most manuscripts. For originals with rich dark shadow levels, scanning with a roller scanner is recommended.
3. Adjust the midtone gamma so that the gray level 11 is around 125. If the 11th level is too small, increase the gamma; otherwise, decrease the gamma.
4. According to the relationship between the RGB values of each level of gray scale, adjust the values of the three channels so that the value of each scale in the three channels is approximately equal. If R = G = 125, B = 119, you can increase the gamma value of the B channel, so that it does not bias ****.
The scanned RGB image must be converted to CMYK before it can be output. During this time, the image was also color-coded and corrected.