Image scanning some insights
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With the development of computer technology and the continuous improvement of people's cultural quality, the readers are increasingly demanding printed materials, especially the quality of color images. At present, the color images of some pictorials, albums, and periodicals are not high in quality, and the originals cannot be restored well. The color distortion is serious. Some colors become pattern blocks, and some are light and dark, and the layers are reversed. In addition to the poor quality of some of the originals, most of these ills are caused by improper scanning color separation techniques. This article will introduce some of the author's experience of scanning images, I hope to be beneficial to everyone!
Establish the correct scanning concept
For image scanning, many operators have misunderstandings, lack of physical and chemical concepts and standardized reduction scanning color separation operation methods, purely leading post-processing, that is, relying on the screen color to make subjective random adjustment, resulting in high-end professional scanners, electric extensions high-end The advanced technology and powerful features of networking have not been fully realized.
In fact, scanning images is not a simple matter. It requires reasonable settings for the scanner's resolution, tone, color and other parameters. If set incorrectly, the scanner may cause a lot of image detail loss, color cast, and black and white field uncertainty during scanning. Even if it is processed by various image software in the later stage, it will only further aggravate the loss of the image, and it will not be able to obtain a similar effect to the original. Therefore, before scanning, it is necessary to establish a correct scanning concept, clarify the basic process of image scanning, correctly set the scanning parameters, and scan out high-quality images.
Image scanning is technical and artistic. It is necessary to set and adjust the parameters of gray balance, tone contrast, color correction and sharpness according to different types of manuscripts in terms of technology, and to deal with the aesthetic aspects of art. The relationship between color tone, saturation, spatial distance, light and dark, and brilliance. The level of the operator in these two aspects 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 technology of scanning color separation and cultivate a higher level of operators.
Select a good scanned original
Scanning the original directly affects the quality of the scanned image. At the same time as selecting the original: look at the surface of the original for scratches, dirt, text, lines, and whether there are any missing strokes. 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 of the reflective paper have interference with other colors, that is, whether there is color cast on the reflective draft image. Third, see if the main colors are accurate. In general, the color of a reflective document (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-tone part; the color contrast is moderate, the color density of the reflection draft is large, and the stereoscopic feeling is strong; the contrast balance is good, the same color is in the high-profile part and The color performance of the dark areas is consistent.
Correctly adjust the display
Many designers have had this problem: when a color image is processed by a computer, it cannot achieve the same effect as the display after output or printing. Therefore, before performing image scanning, it is necessary to adjust the display brightness, display color and other parameters of the display. It is preferable to make these parameters consistent with the parameters to be set by the scanner or slightly higher, so that the screen display effect is basically the same as the actual printed matter. .
Place the original in the best scanning area
Place the original in the best scanning area of the scanner for the best image quality. This optimal scan area is obtained after multiple tests: set all controls of the scanner to automatic or default state, select all areas, and scan a blank, white or opaque sample with low resolution: open it in Photoshop The scanned image of the sample is processed using the Image → Adjust → Tone Homogenize command, and you can see where there are cracks, streaks, and black spots on the scanner. Print this file and cut out the best areas (that is, the most stable areas) to help us place the originals.
Properly placed the scanned object
When processing scanned images, it is sometimes necessary to obtain an image with a tilt 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 is: how to rotate the page on the design image, use the protractor to measure the precise angle of the original rotation, and then scan to get the highest quality image.
Choose the right scan type
Choosing the right type of scan will not only help improve the scanner's recognition success rate, but it will also generate files of the right size. Usually, the scanner provides users with three types of scanning: color, grayscale and black and white. Before scanning, the appropriate scanning type should be selected according to the scanning object and the end use. The "Color" scan type is suitable for scanning color photos. It uses multiple levels of sampling and storage for the red, green and blue channels. This method will generate larger files; the "grayscale" scan type is often used for existing images. There is also a text layout of the text, the file size is moderate; "black and white" scan type is often scanned in black and white originals, when scanning with this type, the scanner uses 1 bit to represent black and white pixels, this way The generated file is minimal.
Now there is a color image whose final result is required to be a grayscale image. Is it directly scanned in grayscale, or is it first scanned in color and then converted to grayscale? 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 richer in level. Then use Photoshop software to convert color images into grayscale images, and the level will be better. On the other hand, if 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 original image is. The resolution of the scanner resolution should be determined based on 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 significantly improve the output, but will increase the storage capacity of the file and reduce the overall work. effectiveness.
In general, if you scan some drawings or images that contain 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 used to display the web page image, the scanning resolution is set to 72dpi, so the generated image file is relatively small, which is conducive to the image transmission on the network; if the image In the end, printing and publishing requires at least 300 dpi resolution.
It is best to pre-sweep
Many operators skip the pre-scan step to save scan time when scanning large-sized photos or documents. In fact, the pre-scan function is very necessary before the official scan, it is the first level to ensure the scanning effect. Pre-sweep has two advantages: First, the pre-sweeped image can directly determine the area to be scanned, crop the image, rotate, etc. to reduce the image processing after scanning; second, observe the pre-scan After the image, you 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 other 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 set all the scanning parameters related to the image as much 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 adjust the image scanning effect to an ideal state.
Finally, it should be noted that after obtaining a satisfactory scanned image after scanning, it is better to sharpen the image. Due to the limitations of the light-receiving components (such as CCD optical quality) 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 sharpness of scanned images by artificially processing, such as the application of Unsharp, Shapren, and Sharpen More effects.