On the Experience of Image Processing in Newspaper Printing
The quality of image processing plays a key role in the quality of newspaper printing. Therefore, when processing images, first ensure that the scanner and the monitor are calibrated before image processing, so that the gray balance of the scanner has been calibrated without color shift, and the color of the monitor should be as close as possible to the printing color. For newsprint printing, the color separation parameters are set in Photoshop: the dot increase is about 30%, the total ink volume is 220% ~ 260%, GCR is adopted, the black version is middle adjusted, and the black version starts at 30% Above, the black version has a maximum limit of 85%.
Image processing steps:
(1) Analyze the manuscript; (2) Improve the color deviation of the image through color balance or curve adjustment. The judgment method is to find the gray part in the image, and adjust the three values ​​of R, G, and B to be equal by adjustment; (3) Use the curve Or color gradation to adjust the depth of the image; (4) convert the image to CMYK mode; (5) determine the black, white, and mid-tone depth of the image; (6) adjust the color of the image; (7) sharpen Processing etc.
Note on image processing:
1. As much as possible, the saturated color should be controlled within the gamut to avoid color distortion. The basic color and the opposite color in the saturated color should be adjusted according to the level and content of the main body of the image.
2. Regardless of whether it is a grayscale image or a color image, the bright tone should not be screened, and the high light area can be screened; the dark tone should not be graded, and the blackness should be enough to avoid affecting the image contrast.
3. As much as possible to ensure the tone level of the image, make the image rich and natural.
4. The sharpening data of the image should be set according to the specific requirements of printing: the radius is generally 0.8 ~ 1.2; the threshold is generally 3 ~ 5.
In addition, in the process of newspaper typesetting, we often encounter the processing of color images. A color image may be RGB mode or CMYK mode. When using Photoshop for processing, how to choose between the two modes, the author talks about his own views.
The image used for platemaking in the color newspaper publishing process must be in CMYK mode, otherwise printing will not be possible, but it does not mean that the image processed in CMYK mode will have a good printing effect. In fact, when processing images with Photoshop, the effect of selecting RGB mode is stronger than the effect of selecting CMYK mode. Only after processing the image in RGB mode, and then converting it to CMYK mode, the output film can be used for plate printing. When performing image processing, if the opened image itself is in RGB mode, you only need to select the RGB mode in the color setting options when scanning with Photoshop. Especially for images downloaded from the Internet, the printing effect after scanning in this mode is better.
In addition to the RGB mode, the device-independent L * a * b * mode also has very good image processing characteristics. L * a * b * mode can edit and process any image (including grayscale image), which can ensure that there is no loss of color when the color mode is converted, and the speed is as fast as the RGB mode, and it is several times faster than the CMYK mode. When converting the RGB mode image to the CMYK mode, there should be an intermediate link, that is, to convert to the L * a * b * mode first. In the process of non-color typesetting, the application of L * a * b * mode to convert images into grayscale images is often used. For an RGB mode image downloaded from the Internet, if you do not use the L * a * b * mode transition and then convert it to a grayscale image, sometimes when you use Fangzheng Feiteng or Weisi software to typeset, sometimes the image cannot be processed typesetting.
It can be seen that when processing color images with Photoshop, L * a * b * mode and RGB mode should be selected as much as possible, and then converted to CMYK mode only as a last resort. Once you have switched to CMYK mode, don't switch back easily. If you really need to, switch to L * a * b * mode before processing the image. If the original image used for scanning is a color image and the image is used for a grayscale layout, do not directly input the original image as a grayscale image. Instead, enter the image in RGB mode, and convert it to L after processing * a * b * mode, and then use the channel sub-command to select the image of the L * channel as the grayscale image for printing. During the operation, it should be noted that it is necessary to ensure the authenticity of the color of the output image in the CMYK mode, and ensure that the image has been completely processed before converting to the CMYK mode.
Processing methods for special types of images:
In addition to grayscale and color images, some special types of images are often involved in image manuscripts. The specific processing methods are:
1. Processing of original large-scan printed manuscripts
Set the scanning resolution to 600dpi and sharpen to none; enter the "Image Menu / Image Size" dialog box and adjust the resolution of the scanned image to reduce it gradually, and the reduction is uneven, up to 200dpi (single The resolution of the color newspaper is 200dpi, and the resolution of the color newspaper is 240dpi); adjust the gradation color of the image; and finally adjust the USM sharpening of the image.
2. Grayscale processing
Scan in RGB mode, after entering Photoshop, convert RGB mode to L * a * b * mode, extract the L * channel as a grayscale file, adjust the grayscale image at this time, and finally perform USM sharpening adjustment on the image .
3. Digital image processing
Enter the "image / image size" in Photoshop, connect the size and resolution, and change the resolution from 72dpi to 200kpi (the resolution of monochrome newspaper is 200dpi, the resolution of colorful newspaper is 240dpi); then change the length of the image , Wide size connection, the resolution will not change at this time, change the image size to the required size; if there is mosaic phenomenon, the image will be blurred first and then sharpened.
4. Processing of duotone images
Scan the CMYK mode, enter Photoshop to convert the CMYK image to grayscale image, convert the grayscale image to dual tone image in the mode, and adjust the dual tone level and color, convert the dual tone image to multi-channel image in the mode A CMYK file, paste each channel of multiple channels into CMYK.
5. Line drawing processing
Scan the grayscale mode, the resolution is 1200dpi, enter the "image / adjustment / threshold" adjustment in Photoshop, adjust the grayscale image to a bitmap, keep the resolution unchanged, and use the "50% threshold" conversion method.
6. Processing of downloading images from the Internet
Since the color range of the RGB mode is larger than the CMYK mode, in order to ensure the printing effect of the image, it is best to use the RGB mode for processing, and finally convert to the CMYK mode. When editing an RGB mode image in Photoshop, select the CMYK preview option in the View menu, that is, edit the image in RGB mode and display the image in CMYK mode. If the original image is a color image, but it is used in a grayscale layout, do not edit the original image directly to grayscale mode during processing. You should input the image in RGB mode, process the image in RGB mode, and convert it to L first. * a * b * mode image, and then use the channel separation command to select the L * channel image as the grayscale image for printing. Note that do not switch between the two modes RGB and CMYK, let alone switch the two modes back and forth, because in the bitmap image editing software, each time the color space of the image is converted, some of the details of the original image will be lost information.
Matters needing attention in the processing of images printed on newsprint; in order to make the colors bright, the main colors should be appropriately increased, or the opposite colors should be appropriately reduced; the dark tone should be properly discarded to maintain the middle and bright tone; the face value of the black and white image of the character should not be too high, To avoid being too dark, the bright tone should be enough.
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