High quality image scanning
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Today's consumers are increasingly demanding print quality, especially the quality of color images. However, the color images of some pictorials, albums, periodicals and magazines are not high in quality, and the color distortion is serious. The originals cannot be restored well, and some of them have poor light and dark reproduction. In addition to the reasons for the poor quality of some of the originals, it is also caused by improper scanning color separation.
Practice has proved that scanning color separation technology is the key to the quality of color image reproduction. The author is here to talk about some of the ideas, I hope to be beneficial to everyone.
The tree produces the correct scanning concept
For image scanning, many operators have misunderstandings, lack of concepts and standardized methods of reducing scanning color separation, relying solely on post-processing, that is, relying on the color of the screen to make subjective random adjustments, resulting in high-end professional scanners and electrical extensions The advanced technologies and powerful features of networking have not been fully realized.
In fact, image scanning is not a simple matter, it needs to make reasonable settings for the scanner's resolution, scanning brightness, hue and other parameters. If it is not set or set incorrectly, it may cause a lot of image details to be lost during the scanning process, resulting in color cast, black and white field uncertainty and so on. Even if it is processed and adjusted by various image software later, it will only further aggravate the loss of the image, and it will not be able to obtain a similar effect to the physical 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 a high-quality image be scanned through the correct parameter setting during a specific image scanning process.
In addition, image scanning is both technical and artistic. It is necessary to reasonably set and adjust parameters such as gray balance, tone contrast, color correction and sharpness according to different types of manuscripts, and to deal with color tone, saturation and spatial distance from the aesthetic point of view of art. , light and dark, light and shadow changes and other relationships. The level of these two aspects of the operator has a great impact on the image quality. Therefore, in order to improve the image quality of current color prints, we must make up our minds to grasp the key link of scanning color separation and cultivate a higher level of operators.
Select a good scanned original
Scanning the quality of the original directly affects the quality of the scanned image. When selecting the original ally, you can see whether the surface of the original is scratched or dirty, whether the text and lines are complete, whether there is a missing pen, or a broken picture. Second, see if the picture is color cast. Under natural light or a standard light source close to daylight color, observe whether the white, gray, black and other decolorizing parts on the original have interference with other colors. Third, see if the main colors are accurate. In general, the color of a reflective manuscript (such as a photo) is slightly more exaggerated than the color of the actual scene, that is, more vivid than the original color. For the reflection of the character, the skin color should be rosy. Fourth, see if the contrast is moderate. The contrast of the reflective draft includes luminance differences, color contrast, and contrast balance. The brightness difference is moderate, there is a rich transition color level between the high-tone part and the dark-adjusted part; the color contrast is moderate, the color density of the reflection draft is large, and the stereoscopic feeling is strong; the contrast is good, the same color is in the high-profile part and The color performance of the dark areas will be consistent.
Correctly adjust the display
Many designers have had this problem; when the color image is processed by the computer, after the output or printing, the effect consistent with the display cannot be obtained. Therefore, in order to avoid the inconvenience caused by the difference between the screen display effect and the actual printed matter, it is necessary to adjust the display brightness, display color and other parameters of the display before the image scanning, it is preferable to make these parameters and the scanner to be set. The parameters are consistent or slightly higher, so strive to not affect the final visual effect due to the display.
Rotate the original in the best scanning area
Place the original in the best scanning area of the scanner for the best, most fidelity image. This optimal scan area was obtained after multiple tests. Set all scanner controls to Auto or Default, select all areas, and scan a blank, white, opaque sample with low resolution. Open the scanned image of the sample in Photoshop and use the "Image → Adjust → Tone Equalization Command" to process it, and you can see cracks, streaks, and black spots on the scanner. Print this file to select the best area (the most stable area) to help the operator rotate the original.
Properly placed the scanned object
When dealing with scanned images, sometimes it is necessary to obtain a tilting effect, and many designers often use professional image software to rotate the image. In fact, this not only wastes time, but also reduces the quality of the image to varying degrees. The correct approach: design how the image is placed on the page, use the protractor to measure the precise angle of the original rotation, and obliquely place the original for scanning, the highest quality image will be obtained.
Choose the right scan type
Choosing the right type of scan will not only help improve the recognition success rate of the scanner, but also generate files of appropriate size. Usually, the scanner provides users with three types of color, grayscale and black and white, which should be based on scanning. Select the appropriate scan type for the difference between the scanned object and the end use. The "Color" scan type is suitable for scanning color photos. It uses multiple levels of sampling and storage for red, green and blue channels. This method will generate larger files; the "Grayscale" scan type is often used. Both the picture and the text are mixed and sampled, and the file size is moderate; the "black and white" scan type is often scanned in black and white. When scanning with this type, the scanner will display black and white according to 1 bit. Pixels, the file size generated in this way is minimal.
There is a color image, and the final result is required to be a grayscale image. Is it directly scanned by grayscale, or is it first scanned by color and then converted to grayscale image? The author's suggestion is to use color scanning. By selecting color scanning, various adjustments can be made to the scanned original, and the amount of color information of the color scanning is large, and the color obtained after scanning is more saturated, and the level is richer. Then use Photoshop software to convert color images into grayscale images, and the level will be better. If the grayscale scanning is directly selected, the color of the image before scanning is lost, and the room for adjustment is very small. The level of the grayscale image after scanning is obviously not rich in color scanning and then converted into a grayscale image.
Choose the right scanning resolution
Scanners usually provide a range of resolutions that can be set. In theory, the higher the resolution is set, the more pixels are scanned per inch, and the more detailed the originals are. The resolution of the scanner should be determined according to the end use of the scanned image. Since the highest resolution of the scanner is obtained by interpolation, scanning with the accuracy of the optical resolution of the scanner will not only have obvious effect on the output. Improvement, on the contrary, increases the storage capacity of files and reduces the overall work efficiency.
In general, when scanning some drawings or images containing text information, you should set the scanning resolution 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 be better distinguished; if the scanned image is only due to the screen display or web page image, the scanning resolution is set to 72dpi, so the generated image size is relatively small, which is conducive to the image transmission on the network; The image will eventually be printed and published, at least 300dpi resolution is required. Of course, if you can use the resolution of 600dpi, it will be better.
Best to pre-sweep
Many users skip the pre-scan step to save scan time when scanning large-sized photos or documents. In fact, before the official scan, pre-scan is very necessary, is the first level to ensure the scanning effect. The pre-sweep has two advantages: one is to directly determine the area to be scanned by pre-sweeping the image, and to crop, rotate, etc. to reduce the image processing process after scanning; Pre-sweeped images can roughly see the color, effect, etc. of the image. If you are not satisfied, you can re-set, adjust, and then scan the scan parameters.
Adjust the scan parameters related to the image
In order to scan out images with good effect and high quality, you not only need to do all the setting work mentioned above, but also must scan all the scanning parameters related to the image as fast as possible, such as the color balance parameters of the scanned image. By adjusting, you can change the overall tonal effect of the scanned image, and the image scanning effect can be accelerated 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 polarity will enhance all of the tones; when there is some color cast in the original image, you can use the Tone tool to make the image look more natural.
Finally, it should be noted that when the user obtains a satisfactory scanned image, it is better to sharpen the image. This is due to the limitations of optoelectronic components (such as CCD and its optical quality and lighting conditions) and the quantization error caused by digital sampling. The scanned images are often not as clear as the original. Therefore, in image processing, it is important to improve the sharpness of the scanned image by artificially processing, such as Unsharp, Sharpen, Sharpen More, but also must grasp the sharpness.