What mode to process color pictures best

In the newspaper typesetting process, often encounter the processing of color pictures, when opening a color picture, it may be RGB mode, it may be CMYK mode. So when using Photoshop, is it using RGB mode or CMYK mode for color picture processing? This article on this issue to discuss the author's views.

In the process of using Photoshop to handle pictures, first of all, you should pay attention to the opening of a picture, whether the CMYK mode of the picture, or RGB mode of the picture, do not in the two modes of each other to turn, not to the two modes of wandering. Because, in the dot matrix picture editing software, each time the picture color space transformation, will lose part of the original picture the detail information. If you turn a picture into RGB mode for a while, and then turn to CMYK mode, the picture's information loss will be very large. Here should be explained that the color newspaper publishing process for Seihan printing of the picture mode must be CMYK mode of the picture, otherwise it will not be able to print. But it is not said that in the processing of the picture in CMYK mode to deal with the printing effect must be very good, or according to the situation to decide. In fact, the use of Photoshop processing pictures to choose RGB mode effect is better than using CMYK mode effect, as long as the RGB mode of processing a good picture, and then converted to CMYK mode of the picture after the output film can be Seihan printing.

In the image processing, if the image opened for processing is the RGB mode of the picture or the original picture in the use of the scanner input process allows the selection of RGB mode for scanning, this situation for the color newspaper typesetting is the best. Use Photoshop to scan the original picture as long as you select the RGB settings option in the Color setting option in the File menu bar, the color picture that is entered by the scanner is the RGB mode picture. In short, without the need to transform the picture mode first, can obtain the RGB mode picture, use this pattern to handle 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. From the following aspects of the discussion on this point.

1. RGB mode is the color mode used by all devices based on optical principles. For example, a monitor that works in RGB mode. RGB mode and the color range is greater than CMYK mode, so, RGB mode can express many colors, especially bright and bright colors (of course, the color of the display must be corrected, will not appear the image color distortion). This color is hard to print when printed. This is also the picture color mode from RGB to CMYK when the screen will darken the main reason. When editing RGB-mode pictures in Photoshop, you must first select the CMYK Preview command in the View menu (if you are using the photo shop as the Chinese version, select the preview option in the View menu bar and select the CMYK option in it), that is, In RGB mode to edit the processing of pictures, and CMYK mode to display pictures, so that operators see the picture on the screen color, is actually printing the color required, this is very important, in the application of printing this is a good picture processing method. Photoshop working in CMYK mode, color channel than RGB one, in addition, it also uses RGB display mode to simulate the CMYK display effect, and CMYK operation mode and based on optical RGB principle completely different, therefore, The use of CMYK mode to deal with the image of a lower efficiency, the processing of the quality of the picture is also poor.

2. Some of the filters in Photoshop do not support CMYK mode when using Photoshop to process pictures. In addition, the editing of a picture often involves many subtle processes, such as the possibility of combining the contents of several pictures, because the original tones of each component are unlikely to be the same, they need to be adjusted, and the parts may be synthesized in some way, filter processed, and so on. No matter what the image processing to achieve the effect, operators want to produce as much as possible and retain a variety of subtle effects, as far as possible to make the screen with real and rich details, because RGB mode color range than CMYK mode is much larger, so, in RGB mode processing picture, throughout the editing process, will get a wider color space and a more subtle editing effect, and these effects, if used well, can be largely preserved. Although eventually have to convert to CMYK mode and there will be a loss of color, but this is much better than the beginning of the color loss of the picture.

3. When you convert an RGB-mode picture to a CMYK-mode picture, the color separation parameter plays a decisive role in how well the picture is converted. The adjustment of the separations parameters will affect the transformation of the picture to a large extent, and the Photoshop image processing software has the ability to control the color separation parameters. In other words, when you need to convert the image processed in RGB mode to CMYK mode for output, in the conversion process through the adjustment of the color separation parameters can reduce the picture in the pattern conversion when the color loss.

4. Currently for the newspaper publication, the use of the picture needs long-term retention, in RGB mode to retain picture data is more ideal. After the color and correction of RGB mode picture data information can become a long-term storage of valid documents, so that future retrieval from the archive of RGB mode pictures can be used on different output devices. For RGB mode picture data information in many future workflow needs to reuse, whether the color separation method is the use of system-level color management method or the use of Photoshop image conversion method is very convenient.

5. In the use of various printing presses, digital proofing equipment or computer monitors for the printing of pictures, proofing, output, observation (and measurement) above the printing and output equipment copied picture color difference is the main way to measure the production of neutral ash required cyan, magenta and yellow amount, printed on the copy system called the gray balance. If the picture is converted to CMYK mode, then reuse different output devices, the picture requires the adjustment of the CMYK image of the high light, midtones and darkened outlets, and change the overall gray balance and color saturation. In order not to affect the quality of picture printing, the amount of black in the picture to be changed, but if you do not modify the black data and printing pictures, will produce bad printing results. For example, the original high-quality sheet-fed printing machine color separations CMYK mode picture, if printing on the web presses will cause rubbing dirty phenomenon, the picture of black volume, the processing method can only be modified CMYK mode picture. RGB-mode pictures can use a larger range of RGB tones to reproduce brighter, more saturated colors. However, when the picture is separated into CMYK, all the pixels in the picture are within the CMYK tonal range.

Through the above discussion, we can see that using Photoshop to process color pictures should be used in RGB mode. But in the course of operation should be noted: the use of RGB mode of processing the picture must ensure that the CMYK mode output when the authenticity of the picture color; Use RGB mode to process the picture to be sure that the picture has been completely processed and then converted to CMYK mode picture, preferably leave an RGB mode of the picture standby.

In addition to working with images in RGB mode, Photoshop's lab color model has good features. RGB mode is based on the optical principle, and CMYK mode is the color of the paint reflected light, the advantage of the lab model is that it makes up for the previous two color mode deficiencies. RGB in blue and green between the transition color too much, green and red transition between too little, CMYK mode in the process of editing the image of the loss of color is more, and lab mode in these areas are compensated. Lab mode consists of three channels, the L channel represents brightness, it controls the brightness and contrast of the picture, a channel includes a color from dark green (low brightness value) to gray (medium brightness value) to Liang red (high brightness value), b channel includes the color from bright blue (low brightness value) to gray to yellow (high brightness value). Lab mode is similar to RGB mode, and the blending of colors produces brighter colors. Only the value of the brightness channel affects the hue and shade changes. You can consider lab mode as a mode of two-channel RGB mode plus a brightness channel. Lab mode is device-independent, and you can edit any one of the pictures (including the grayscale picture) in this mode, and it is as fast as RGB mode, several times faster than the CMYK mode. Lab mode ensures that the colors in CMYK range are not lost when the color mode is converted. If you convert an RGB-mode picture to CMYK mode, you should add an intermediate step to the action step, which translates to Lab mode first. In the typesetting process of non color newspapers, it is often used to convert pictures into grayscale images using lab mode. For some of the Internet download the RGB mode of pictures, if you do not use the lab mode transition and then converted to grayscale, then in the founder or the use of risperidone typesetting software layout, sometimes the picture can not be typesetting.

Thus, in the editing process picture, as far as possible with lab mode or RGB mode, in the last resort to CMYK mode. And once converted to CMYK mode picture, do not easily again turn back, if it is really necessary, turn into lab mode for the image processing. If the original image used to scan the input is a color picture, but the picture is used in grayscale layout, with the scanner input picture, do not direct the original picture into the grayscale mode, you should use RGB mode input picture, with RGB mode of processing the picture, the first into the lab mode of the picture, and then through the channel separation command, Select a picture of the L channel as a grayscale image for printing.

Most operators in the actual processing of the picture, are more straightforward, what kind of images need to be scanned directly with the scanner to the desired picture mode, and then a little processing that is used for typesetting, in the printing also looks like the case. In fact, to really get a good picture printing effect or do not be afraid of trouble, according to the standard procedures for the operation.