Today's consumers are increasingly demanding print quality, especially the quality of color images. However, the color images of some pictorials, picture albums, periodicals and magazines are not printed with high quality, and the color distortion is serious, so the originals cannot be restored well, and some have poor light and dark reproduction. All these disadvantages, in addition to the reasons for the poor quality of some originals, are also caused by improper color separation.
Practice has proved that scanning color separation technology is the key to the quality of color image reproduction. The author talks about some experiences here, hoping to benefit everyone.
Tree correct scanning concept
For image scanning, many operators have wrong understanding, lack of concepts and standardized operation methods for restoring scanning separations, and rely solely on post-processing, that is, relying on screen colors for subjective arbitrary adjustments, resulting in high-end professional scanners and high-end electronic extension The advanced technology and powerful functions of networking have not been brought into full play.
In fact, image scanning is not a simple matter, it needs to set the parameters of the scanner's resolution, scanning brightness, hue and other parameters reasonably. If it is not set or improperly set, a large amount of image details may be lost during the scanning process, causing color casts and unclear black and white fields. Even if it is processed and adjusted by various image software in the later stage, it will only further aggravate the loss of the image and cannot obtain the effect similar to the real image. Therefore, before scanning, it is necessary to establish a correct scanning concept and clarify the basic process of image scanning. Only in this way can high-quality images be scanned through correct parameter settings during a specific image scanning process.
In addition, image scanning is both technical and artistic. It is necessary to set and adjust the parameters of gray balance, tone contrast, color correction and sharpness from the technical aspects according to different types of manuscripts, but also to deal with the color tone, saturation and spatial distance from the aesthetic point of view of art , Light and dark, light and shadow changes, etc. The level of these two aspects of the operator has a great influence on the image quality. Therefore, to improve the image quality of current color prints, we must make up our mind to grasp the key link of scanning color separation, and train a higher level of operators.
Selected scanned original
The quality of the scanned manuscript directly affects the quality of the scanned image. When selecting the manuscript ally, see if the manuscript surface is scratched or dirty, whether the text and lines are complete, whether there are missing pens, broken drawings, etc. Second, see if the picture is color cast. Under the standard light source of natural light or near daylight color, observe whether the white, gray, black and other achromatic parts on the original are interfered by other colors. Three to see whether the main colors are accurate. In general, the colors of reflective drafts (such as photos) are slightly more exaggerated than the colors of actual scenes, that is, they are more vivid than the original colors. For reflection drafts with characters as the main body, the facial skin color should be rosy as the standard. Four to see whether the contrast is moderate. The contrast of the reflection draft includes brightness difference, color contrast and contrast balance. Moderate brightness difference, there are rich transitional color levels between high-key parts and dark-tone parts; moderate color contrast, the reflection color density is large, and has a strong three-dimensional sense; good contrast balance, the same color in high-key parts and The color performance of the dark areas will be very consistent.
Adjust the monitor correctly
Many designers have had such troubles; after the color image is processed by the computer, after output or printing, it is impossible to obtain the same effect as the display. Therefore, in order to avoid the inconvenience caused by the difference between the screen display effect and the actual printed matter, before performing image scanning, it is necessary to adjust the display brightness, display color and other parameters of the monitor. It is best to let these parameters and the scanner be set The parameters are kept the same or slightly higher, so as not to affect the final visual effect because of the display.
Rotate the original in the optimal scanning area
Place the original in the best scanning area of ​​the scanner to get the best and most fidelity image effect. This optimal scanning area is obtained after many tests. Set all controls of the scanner to automatic or default state, select all areas, and scan a blank, white, opaque sample with low resolution. Open the scanned image of the sample in Photoshop and process it using the “Image → Adjust → Tone Equalization Commandâ€, you can see how there are cracks, stripes and black spots on the scanner. Print this file and select the best area (that is, the most stable area) to help the operator rotate the original.
Place the scanned object correctly
When processing scanned images, it is sometimes necessary to obtain a tilt effect, and many designers often use professional imaging software to rotate the image. In fact, this not only wastes time, but also reduces the quality of the image to varying degrees. Correct practice: Design how the image is placed on the page, use a protractor to measure the exact angle of the original rotation, and lay the original diagonally for scanning to get the highest quality image.
Choose the right scan type
Choosing the appropriate scan type will not only help to increase the recognition success rate of the scanner, but also generate a file of the appropriate size. Generally, the scanner provides users with three scan types: color, grayscale and black and white. Choose the right scan type according to the scan object and the end use. The "color" scan type is suitable for scanning color photos. It requires multi-level sampling and storage of the red, green, and blue channels. This method will generate a larger file size; the "grayscale" scan type is often used Mixed graphic and text samples with both pictures and text, the file size is moderate; "black and white" scanning type is common in white and black manuscript scanning, when using this type of scanning, the scanner will indicate black and white according to 1 digit Pixels, the file size generated in this way is the smallest.
An existing color image, the final result of which requires a grayscale image, then whether to scan directly in grayscale, or first scan in color and then convert to grayscale image? The author's suggestion is that it is best to use color scanning. Choosing color scanning can make various adjustments to the scanned original. At the same time, the color information of color scanning is large, and the colors obtained after scanning will be more saturated and the layers will be richer. Then use Photoshop software to convert the color image into a grayscale image, the layer will be better. If you choose gray-scale scanning directly, the color of the image before scanning is lost, and the room for adjustment is very small. The gray-scale image layer after scanning is obviously not rich in color and then converted into gray-scale image.
Choose the right scan resolution
Scanners usually provide a range of resolution that can be set. In theory, the higher the resolution, the more pixels per inch of the scanned image, and the richer the original details expressed. The resolution setting of the scanner should be determined according to the final use of the scanned image. Since the highest resolution of the scanner is obtained by interpolation, scanning with an accuracy that exceeds the optical resolution of the scanner will not only have an obvious effect on the output effect. Improvements, on the contrary, increase the storage capacity of files for no reason and reduce the overall work efficiency.
In general, when scanning some engineering drawings or images containing text information, the scanning resolution should be set as high as possible, so that the lines or text in the image will be more improved when the scanning resolution is improved. Close to the original appearance, each line stroke can also be distinguished relatively well; if the scanned image is only due to the screen display or web page image, the scanning resolution can be set to 72dpi, the size of the generated image is relatively small, which is conducive to the image transmission on the Internet; if The image will eventually be printed and published, at least 300dpi resolution is required, of course, 600dpi resolution will be better.
Prescan
Many users will skip the pre-scanning step to save scanning time when scanning large-sized photos or documents. In fact, before formal scanning, pre-scanning is very necessary and is the first level to ensure the scanning effect. The pre-scan has two advantages: one is that the pre-scanned image can be used to directly determine the area to be scanned, and the image is cropped, rotated, etc. to reduce the image processing process after the scan; the second is by observation The pre-scanned image can roughly see the color and effect of the image. If you are not satisfied, you can set and adjust the scanning parameters again, and then scan again.
Adjust the scanning parameters related to the image
In order to scan images with good effect and high quality, not only do all the above-mentioned settings work, but also all the scanning parameters related to the image, such as the color balance parameters of the scanned image, must be as fast as possible. By adjusting, you can change the overall hue effect of the scanned image and speed up the image scanning effect to a more ideal state; if you want to adjust the saturation of the color in the scanned image, you can control the saturation by dragging the slider on the saturation slider, Choosing the correct saturation will strengthen all the hues; when there is a certain color cast in the original image, you can use the hue tool to adjust it to make the image look more natural.
Finally, it should be explained that when the user gets a satisfactory scanned image, it is better to sharpen the image. This is due to the limitations of photoelectric components (such as CCD and its optical quality and lighting conditions, etc.) and the quantization error caused by digital sampling, the scanned image is often not as clear as the original. Therefore, in image processing, it is important to improve the clarity of the scanned image through artificial processing, such as the Unsharp, Sharpen, Sharpen More effect, but at the same time, we must also grasp the sharpness size.
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