The best mode for processing color pictures in newspaper layout

In the typesetting process of newspapers or magazines, the processing of color pictures is often encountered. When a certain color picture is opened, it may be RGB mode or CMYK mode. So when using Photoshop, do you use RGB mode or use CMYK mode for color image processing? This article talks about the author's opinion on this issue.

In the process of using Photoshop to process the image, the first thing to note is that for an open image, whether it is the CMYK mode picture or the RGB mode picture, do not switch between the two modes. Turn both modes around. Because, in the dot matrix picture editing software, every time the picture color space is converted, the original picture details will be lost. If you turn a picture into an RGB mode for a while and turn it into a CMYK mode, the information loss of the picture will be great. It should be said here that the picture mode used for platemaking during the publication of color newspapers must be a picture of CMYK mode, otherwise it will not be possible to print. However, it does not mean that the printing effect of processing pictures in CMYK mode during image processing will be very good, or it should be determined according to the situation. Its practical Photoshop processing picture selection RGB mode effect is stronger than the use of CMYK mode effect, as long as the RGB mode after processing the good picture, and then convert it to CMYK mode picture output film can be plated and printed.

During image processing, if the picture opened for processing is an RGB mode picture itself, or the original picture is allowed to select the RGB mode for scanning using the scanner input process, this is a good situation for the color newspaper layout. Now. When you use Photoshop to scan the original image, just select the RGB setting option in the color setting option in the file menu bar. The color picture input through the scanner is the picture in RGB mode. In short, without first converting the picture mode, you can get pictures in RGB mode and use this mode to process the pictures. Especially for pictures downloaded from the Internet, you must ensure the printing effect of pictures. Use RGB mode for processing. The discussion of the following aspects can explain this point of view.

(1) RGB mode is the color mode used by all devices based on optical principles. For example, monitors work in RGB mode. The color range of the RGB mode is larger than the CMYK mode. Therefore, the RGB mode can express many colors, especially bright and bright colors (of course, the color of the display must be corrected so that no picture color distortion occurs). This color is difficult to print when printing. This is also the main reason why the picture becomes dark when converting the picture color mode from RGB to CMYK. When editing RGB mode pictures in Photoshop, you must first select the CMYKPreview command in the View menu. (If you are using Photoshop for the Chinese version, select the View option in the bright map menu bar and select the CMYK option.) That is, using RGB mode to edit and process pictures, and displaying pictures in CMYK mode, so that the color of the picture on the display screen seen by the operator is actually the color needed during printing. This is very important when applied to printing. This counts a very good image processing method. When Photoshop is working in CMYK mode, the color channel is one more than RGB. In addition, it uses the RGB display mode to simulate the display effect of CMYK, and the operation mode of CMYK is completely different from the optical TGB principle. Therefore, The efficiency of processing pictures with the CMYK mode is lower, and the quality of the processed pictures is also worse.

(2) Some filters in Photoshop do not slow down the CMYK mode when using Photoshop to process images. In addition, the picture editing process often goes through many subtle processes. For example, it may be necessary to combine the contents of several pictures together. Since the original colors of the various components cannot be the same, they need to be adjusted. Somehow synthesize and perform filter processing and so on.

Regardless of the effect of the picture processing, the operator wants to create and retain as many subtle effects as possible, to make the picture as real and rich as possible, since the color range of the RGB mode is much larger than the CMYK mode. Therefore, when the image is processed in RGB mode, a wider color space and slightly more varied editing effects will be obtained during the entire editing process, and these effects, if used well, can be retained for the most part. Although in the end it still had to be converted to CMYK mode and there was definitely a loss of color, it was much better than letting pictures lose color from the beginning.

(3) When converting an RGB mode picture into a CMYK mode picture, the color separation parameter will play a decisive role in the effect of the picture conversion. The adjustment of color separation parameters will affect the conversion of pictures to a large extent. Photoshop image processing software has the ability to control color separation parameters. In other words, when it is necessary to convert a picture processed in the RGB mode into the CMYK mode for output, adjustment of the color separation parameter in the conversion process can reduce the color loss when the picture is converted in the mode.

(4) At present, for newspaper publishing, the pictures used need to be retained for a long time. It is ideal to retain the picture data in RGB mode. After the correction and correction of the RGB mode picture data information can become a long-term storage of valid documents, so that future retrieval of RGB mode pictures from the archive can be known on different output devices. For RGB mode image data information to be reused in many future publishing workflows, it is very convenient whether the color separation method uses the system-level color management method or the image conversion method in Photoshop.

(5) When printing, proofing, and outputting pictures using various printers, digital proofing devices, or computer monitors, the main method for observing (and measuring) the color difference of pictures reproduced by the above printing output device is to measure the generation of neutrality. The amount of cyan, magenta, and yellow required for ash is printed as the gray balance of the replication system. If the picture is converted to CMYK mode, when the different output devices are reused, the picture needs to adjust the highlight, midtone, and dark tone points of the CMYK picture and change the total gray balance and color saturation. In order not to affect the print quality of the picture, the amount of black in the picture has to be changed, but if the picture is printed without correcting the black data, a bad print result will be produced. For example, a CMYK-mode image that was originally color-separated by a high-quality sheet-fed press would have a large amount of ink in the picture if it was printed on a web press. Its processing method could only be to modify the CMYK mode picture. The RGB mode picture can use a larger RGB tone range to reproduce brighter, more saturated colors. However, after the picture is separated into CMYK, all the pixels in the picture are within the CMYK tone range.

As can be seen from the above discussion, using Photoshop to process color pictures should be done using RGB mode as much as possible. However, during operation, it should be noted that the pictures processed using the RGB mode must ensure the authenticity of the picture colors when outputting in the CMYK mode, and the pictures processed using the RGB mode must be sure that the pictures are completely processed and then converted into CMYK mode pictures. It is best to leave a picture in RGB mode for backup.

In addition to processing images in RGB mode, Photoshop's Lab color mode also has good features. The RGB mode is based on the optical principle, and the CMYK mode pigment reflects the color mode of the light. The advantage of the Lab mode is that it compensates for the deficiencies of the previous two color modes. RGB has too much transition color between blue and green, too little color transition between green and red, CMYK mode loses more color during editing and processing of pictures, and Lab mode has both Compensated. The Lab mode consists of three channels. The L channel represents the brightness. It controls the brightness and contrast of the picture. The colors included in the a channel range from dark green (low brightness) to gray (middle brightness) to bright pink (high brightness). The b channel includes colors ranging from bright blue (low brightness) to gray to yellow (high brightness). Lab mode is similar to RGB mode, and a mixture of colors will produce brighter colors.