Experience in image processing in newspaper printing
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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 display are calibrated before image processing, so that the gray balance of the scanner has been calibrated without color cast, and the color of the display should be as close as possible to the printing color. For newsprint printing, the color separation parameter setting in Photoshop: the dot gain is about 30%, the total ink volume is 220%~260%, the GCR is used, the black version is the middle tone, and the black version is 30%. Above, the maximum limit of the black version is 85%.
Image processing steps:
(1) Analyze the original; (2) Improve the color shift of the image by color balance or curve adjustment. The method of judging is to find the gray part in the image, and make the three values of R, G, and B equal by adjustment; (3) Using the curve Or color gradation to adjust the depth of the image; (4) convert the image to CMYK mode; (5) determine the black and white field of the image and the depth of the middle tone; (6) adjust the color of the image; (7) sharpen Processing and so on.
Image processing notes:
1. Control the saturated color as much as possible within the gamut to avoid color distortion. The basic and opposite colors in the saturated color are adjusted according to the level and content of the image body.
2. Regardless of whether it is a grayscale image or a color map, the brightness should be as high as possible, and the high-light area should be out of the net; the darkness should not be level, and the blackness should be enough to avoid affecting the image contrast.
3. As much as possible to ensure the level of the image, so that the image is 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, the processing of color images is often encountered. A color image may be in RGB mode or CMYK mode. When using Photoshop for processing, how to choose between the two modes, the author talked about their own views.
The image used for plate-making in the process of color newspaper publishing 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. The image can be processed only by processing the image in RGB mode and then converting it to CMYK mode. When performing image processing, if the image being opened is itself in RGB mode, just select the RGB mode in the color setting option when scanning with Photoshop. Especially for images downloaded from the Internet, the printing effect after scanning with this mode is better.
In addition to the RGB mode, the device-independent L*a*b* mode also has excellent image processing characteristics. L*a*b* mode can edit and process any image (including grayscale image), which can ensure that the color mode is not lost when the color mode is converted, and the speed is as fast as RGB mode, and several times faster than CMYK mode. When converting an RGB mode image to CMYK mode, there should be an intermediate link, which is first converted to L*a*b* mode. In the non-color typesetting process, it is often used to convert an image into a grayscale image by applying the L*a*b* mode. For an image of RGB mode downloaded from the Internet, if you do not use the L*a*b* mode transition and then convert to grayscale image, sometimes you can't image the image when you use the Founder Feiteng or Weiss software to typeset. 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 converted to CMYK mode when it is unavoidable. Once you switch to CMYK mode, don't switch back easily. If you really need it, you can process the image after converting it to L*a*b* mode. If the original image used for scanning is a color image and the image is used for grayscale layout, do not directly input the original image as a grayscale image. You should input the image in RGB mode and convert it to L first after processing. *a*b* mode, then use the channel sub-command to select the image of the L* channel as the grayscale for printing. Pay attention during the operation: Be sure to ensure the authenticity of the color of the CMYK mode output image, and ensure that the image is completely processed before converting to CMYK mode.
Special type image processing method:
In addition to grayscale images and color images in image manuscripts, some special types of images are often involved, and the specific processing methods are as follows:
1. Processing of original large printed originals
Set the scanning resolution to 600dpi and the sharpening to none. Go to the Image Menu/Image Size dialog box and adjust the resolution of the scanned image to gradually decrease it, and the amplitude of the reduction is not uniform until 200dpi (single The resolution of the color report is 200 dpi, and the resolution of the color report is 240 dpi); the image is adjusted in layer color; finally, the image is subjected to USM sharpening adjustment.
2. Grayscale processing
Scan in RGB mode, change the RGB mode to L*a*b* mode after entering Photoshop, extract L* channel as grayscale file, adjust the grayscale image at this time, and finally adjust the image to USM sharpening. .
3. Digital image processing
Enter the "image/image size" in Photoshop, connect the size to the resolution, change the resolution from 72dpi to 200kpi (the resolution of the monochrome report is 200dpi, the resolution of the color report is 240dpi); then the length of the image The wide size is connected, and the resolution does not change at this time, and the image size is changed to the required size; if there is a mosaic phenomenon, the image is first blurred and then sharpened.
4. Duotone image processing
Scan the CMYK mode, enter the Photoshop to convert the CMYK image to a grayscale image, convert the grayscale image to a two-tone image in the mode, and adjust the two-tone layer and color, and convert the two-tone image into a multi-channel image in the mode. A CMYK file that pastes each channel in multiple channels into CMYK.
5. Line drawing processing
Scan the grayscale mode with a resolution of 1200dpi. Enter the “Image/Adjust/Threshold” adjustment in Photoshop, convert the grayscale image into a bitmap, keep the resolution unchanged, and use the “50% threshold” conversion method.
6. Processing of images downloaded 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 better to use the RGB mode for processing and finally to convert to the CMYK mode. When editing an image in RGB mode 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 the grayscale layout, do not edit the original image directly into the grayscale mode during processing. You should input the image in RGB mode, and process the image well in RGB mode, and convert it to L first. *A*b* mode image, and then through the channel separation command, select the L* channel image as the gray image for printing. Note that do not convert between RGB and CMYK modes. Do not transfer the two modes. Because in bitmap image editing software, each time the image color space is converted, some of the original image details will be lost. information.
Note on the processing of the image printed on newsprint; in order to make the color brighter, the main color should be appropriately increased, and the opposite color should be appropriately reduced; the dark adjustment and the bright tone should be appropriately discarded; the face value of the black and white image of the character should not be too high. So as not to be too dark, the bright tone should be enough to do enough.