Image Processing in Newspaper Printing

The quality of image processing plays a key role in newspaper printing quality. Therefore, when processing images, first ensure that the scanner and the display are calibrated before image processing, so that the gray balance of the scanner has been calibrated without color cast, and the colors of the display should be as close as possible to the printing color. For newsprint printing, the setting of color separation parameters in Photoshop: dot gains of around 30%, total ink volume of 220%~260%, GCR, black tone for middle tone, and black dot tone for 30%. Above, the maximum limit of the black edition is 85%.

Image processing steps:

(1) Analyze the manuscript; (2) Improve the color cast of the image by color balance or curve adjustment. The judgement method is to find the gray part of the image, adjust the three values ​​of R, G, and B to be equal; (3) use the curve Or color scale to adjust the depth of the image; (4) to convert the image to CMYK mode; (5) to determine the depth of the black, white field, and midtones of the image; (6) to adjust the image color; (7) to sharpen Processing and so on.

Image processing considerations:

1. As much as possible, the saturated color is controlled within the color gamut so as not to cause color distortion. The basic color and the opposite color in the saturated color are adjusted according to the level and content of the image body.

2. No matter if it is a grayscale image or a color image, the bright tone should not be netted, and the high light area can be eliminated. The dark tone should not be combined with the black level, so as not to affect the image contrast.

3. As much as possible to ensure the tone 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, the processing of color images is often encountered during the layout of newspapers. A color image may be an RGB mode or a CMYK mode. When using Photoshop for processing, how to choose the two modes, I talk about their own views.

The image used for platemaking in the process of publishing colored newspapers must be in the CMYK mode. Otherwise, it will not be possible to print. However, it does not mean that the images processed in the CMYK mode must have good printing effects. In fact, when you use Photoshop to process images, the effect of selecting RGB mode is stronger than selecting CMYK mode. Only in the RGB mode image processing, and then converted to CMYK mode, the output film can be plated. 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 option 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 good image processing characteristics. L*a*b* mode can edit and process any image (including grayscale). It can ensure no color loss 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 converted to L*a*b* mode first. In the process of achromatic typesetting, the application of the L*a*b* mode to convert an image to a grayscale image is often used. For an image downloaded from the Internet in RGB mode, if you do not use the L*a*b* mode transition and convert it to a grayscale image, sometimes you cannot perform the image when using the Founder Fetion or Wyse software to typeset. typesetting.

It can be seen that when using Photoshop to process color images, we should use L*a*b* mode and RGB mode as far as possible, and convert it to CMYK mode when we have to. Once it is converted to CMYK mode, it will not be easy to turn back. If it is really needed, it will be processed after converting to L*a*b* mode. If the original image used for scanning is a color image and the image is used in a grayscale layout, do not input the original image directly as a grayscale image. You should input the image in RGB mode, and convert it to L first. *a*b* mode, then use the channel subcommand to select the L* channel image as the grayscale for printing. During operation, care should be taken to ensure that the CMYK mode outputs the true color of the image, ensuring that the image is fully processed and then converted to the CMYK mode.

Special types of image processing methods:

In addition to grayscale images and color images, the image manuscript often involves some special types of images. The specific processing methods are as follows:

1. Processing of original large scanned print manuscripts

Set the scan resolution to 600 dpi and set Sharpness to None; enter the "Image Menu/Image Size" dialog box, adjust the resolution of the scanned image to gradually reduce it, and the amplitude of the reduction is not even until 200 dpi (single) The resolution of the color report is 200dpi, the resolution of the color newspaper is 240dpi); the color of the image is adjusted; finally, the image is subjected to USM sharpening adjustment.

2. Grayscale processing

Scan in RGB mode, enter Photoshop, convert RGB mode to L*a*b* mode, extract L* channels as grayscale files, adjust grayscale at this time, and finally perform USM sharpening on the image .

3. Digital image processing

Enter the “image/image size” in Photoshop, connect the size and resolution, change the resolution from 72dpi to 200kpi (the resolution of the monochrome report is 200dpi, the resolution of the color newspaper is 240dpi); then the length of the image , Wide size connectivity, resolution will not change at this time, change the image size to the required size; if there is a mosaic phenomenon, the image will be blurred and then sharpened.

4. Two-tone image processing

Scan CMYK mode and convert CMYK image to grayscale image in Photoshop. In the mode, convert the grayscale image to a bi-tonal image, and adjust the duotone level and color. In the mode, convert the dual-tone image to a multi-channel image. A CMYK file that puts each channel of multiple channels into CMYK.

5. Line graph processing

Scanning grayscale mode, the resolution is 1200dpi, enter “Photoshop/Adjustment/Threshold” adjustment in Photoshop, convert the grayscale image to bitmap, keep the resolution unchanged, and use the “50% threshold” conversion method.

6. Downloading images from the Internet

Because 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 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 is used in a grayscale layout, do not edit the original image directly to the grayscale mode during processing. Use the RGB mode to input the image. Use the RGB mode to process the image and convert it to L first. *a*b* mode image, then through the channel separation command, select the L* channel image as the grayscale image for printing. Note that do not convert between RGB and CMYK modes, not to transfer the two modes, because in the bitmap image editing software, each time the image color space conversion, will lose part of the original image details information.

Note on the processing of newsprint-printed images; To make the colors brighter, to properly amplify the main colors, reduce or not use the opposite colors properly; properly set the dark tone to protect the medium and bright tone; the black-and-white image of the character can't be too high. To avoid being too dark, bright tone should be enough to do enough.