The best mode to deal with color pictures in the t

The best mode to deal with color pictures in newspaper typesetting

in the process of newspaper or magazine typesetting, we often encounter the processing of color pictures. When opening a color picture, it may be RGB mode or CMYK mode. When using Photoshop, do you use RGB mode or CMYK mode for color image processing? This article talks about the author's views on this issue

in the process of using Photoshop to process pictures, you should first pay attention to one thing. For an open picture, whether it is a picture in CMYK mode or an RGB mode, do not switch between the two modes, let alone turn the two modes around. Because in the dot matrix image software, every time the image color space is converted between the exterior wall insulation materials, a part of the details of the original image will be lost. If you turn an image into RGB mode and CMYK mode for a while, the information loss of the image will be great. It should be said here that the picture mode used for plate making and printing in the publishing process of color newspapers must be the picture of CMYK mode, otherwise it will not be printed. However, it does not mean that the printing effect of processing pictures in CMYK mode must be very good when processing pictures, but it should be determined according to the situation. In fact, the effect of choosing RGB mode for Photoshop processing pictures is stronger than that of using CMYK mode. As long as the pictures are processed in RGB mode, and then converted into CMYK mode pictures, and then output the film, you can make plates and print

during image processing, if the image opened for processing is an RGB image itself, or the original image is allowed to be scanned in RGB mode during the scanner input process, this situation is no better for the layout of color newspaper. When using Photoshop to scan the original picture, as long as the RGB setting option in the color setting option is selected in the file menu bar, the color picture input through the scanner is the picture in RGB mode. In a word, if you can get the picture in RGB mode without first transforming the picture mode, you can use this mode to process the picture, especially the picture downloaded from the Internet. In order to ensure the printing effect of the picture, you must use RGB mode for processing. The following aspects can illustrate this point

(1) RGB mode is the color mode adopted by all devices based on optical principles. For example, the display works in RGB mode. The color range of RGB mode is larger than that of CMYK mode, so RGB mode can show many colors, especially bright and bright colors (of course, the color of the display must be corrected to avoid the distortion of picture color). This color is difficult to print. This is also the main reason why the picture will darken when the picture color mode is converted from RGB to CMYK. When using RGB mode in Photoshop, but it is related to people's life, you must first select the cmykreview command in the View menu (if using Photoshop in Chinese, select the view option in the bright image menu bar, and then select the CMYK option), that is, use RGB mode to process the image, and use CMYK mode to display the image, so that the operator can see the color of the image on the display screen, In fact, it is the color required for printing, which is very important. It is a good image processing method when applied to printing. When Photoshop works in CMYK mode, there is one more color channel than RGB. In addition, it also uses RGB display mode to simulate the display effect of CMYK. Moreover, the operation mode of CMYK is completely different from the TGB principle based on optics. Therefore, the efficiency of processing pictures in CMYK mode is lower, and the quality of processing pictures is also worse

(2) when using Photoshop to process pictures, some filters in Photoshop do not support CMYK mode. In addition, the processing of pictures often goes through many subtle processes. For example, it may be necessary to combine the contents of several pictures. Because the primary color tones of each component cannot be the same, they need to be adjusted. It may also be necessary to make each component synthesize and filter in some way

no matter what effect the image processing wants to achieve, the operator hopes to produce and retain all kinds of subtle effects as much as possible, and make the image have real and rich details as much as possible. Because the color range of RGB mode is much larger than that of CMYK mode, when processing images in GB mode with R performance characteristics, in the whole processing process, a wider color space and national micro variable effects will be obtained. If these effects are used well, Most of them can be kept. Although we still have to switch to CMYK mode in the end and there will definitely be color loss, it is much better than losing the color of the picture at the beginning

(3) when converting RGB mode pictures to CMYK mode pictures, color separation parameters will play a decisive role in the effect of picture conversion. The adjustment of color separation parameters will greatly affect the conversion of pictures. Photoshop Image processing software has the ability to control color separation parameters. In other words, when the picture processed in RGB mode needs to be converted into CMYK mode for output, the color loss during mode conversion can be reduced by adjusting the color separation parameters during the conversion process

(4) at present, for newspaper publishing, the pictures used need to be retained for a long time, and it is ideal to retain the picture data in RGB mode. After color correction and correction, the RGB mode image data information can become an effective document for long-term storage, so that the RGB mode images retrieved from the archive in the future can be known on different output devices. When RGB mode image data information needs to be reused in many publishing workflow in the future, it is very convenient whether the color separation method is system level color management method or image conversion method in Photoshop

(5) when using various printing machines, digital proofing equipment or computer monitors to print, proofing and output pictures, the main method to observe (and measure) the color difference of the pictures copied by the above printing output equipment is to measure the amount of cyan, magenta and yellow required to produce neutral gray, which is called the gray balance of the replication system in printing. If the picture is converted to CMYK mode, when reusing different output devices, the picture requires adjusting the highlight, intermediate and dark points of CMYK picture, and changing the total gray balance and color saturation. In order not to affect the printing quality of the picture, the amount of black in the picture should be changed, but printing the picture without correcting the black data will produce bad printing results. For example, CMYK mode pictures that were originally color separated by a high-quality sheet fed printer will have a large amount of ink in the pictures if they are printed on a web press, and the processing method can only be to modify the CMYK mode pictures. RGB mode pictures can use a larger RGB hue range to reproduce brighter and more saturated colors. However, after the picture is divided into CMYK, all pixels in the picture are within the CMYK hue range

it can be seen from the above discussion that RGB mode should be used as much as possible to process color pictures with Photoshop. However, in the process of operation, it should be noted that pictures processed in RGB mode must ensure the authenticity of picture colors when output in CMYK mode; When using RGB mode to process pictures, make sure that the pictures have been completely processed before converting to CMYK mode pictures. It is best to leave an RGB mode picture for standby

in addition to processing pictures in RGB mode, Photoshop's Lab color mode also has good characteristics. RGB mode is based on optical principle, while CMYK mode is the color mode in which pigments reflect light. The advantage of lab mode is that it makes up for the shortcomings of the previous two color modes. RGB has too many transition colors between blue and green, and too few transition colors between green and red. CMYK mode loses more colors in the process of processing pictures, and lab mode compensates in these aspects. The lab mode consists of three channels. The L channel represents brightness, which controls the brightness and contrast of the picture. The color of channel a ranges from dark green (low brightness value) to gray (medium brightness value) to bright pink (high brightness value), and the color of channel B ranges from bright blue (low brightness value) to gray to burnt yellow (high brightness value). Lab mode is similar to RGB mode, and the mixing of colors will produce brighter colors

sound take the surface Rockwell hardness tester to indicate: