Comparison of processing modes of color pictures in newspaper typesetting
We are a big printing company in Shenzhen China . We offer all book publications, hardcover book printing, papercover book printing, hardcover notebook, sprial book printing, saddle stiching book printing, booklet printing,packaging box, calendars, all kinds of PVC, product brochures, notes, Children's book, stickers, all kinds of special paper color printing products, game cardand so on.
For more information please visit
http://www.joyful-printing.com. ENG only
http://www.joyful-printing.net
http://www.joyful-printing.org
email: info@joyful-printing.net
In the process of typesetting newspapers or magazines, the processing of color pictures is often encountered. When a certain color picture is opened, it may be in RGB mode or CMYK mode. So when using Photoshop, is it using 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 the fact that for a picture that is opened, whether it is a CMYK mode picture or an RGB mode picture, do not switch between the two modes, let alone Turn the two modes around. Because, in the in-place picture editing software, each time the picture color space is converted, part of the original picture details will be lost. If you turn a picture into RGB mode for a while and then switch to CMYK mode for a while, the information loss of the picture will be very large. What should be said here is that the picture mode used for plate making in the process of color newspaper publishing must be a picture of CMYK mode, otherwise it will not be able to print. However, it does not mean that the printing effect of processing pictures in CMYK mode when performing image processing is very good, or it depends on the situation. Its practical Photoshop processing image selection RGB mode effect is stronger than the use of CMYK mode, as long as the image is processed in RGB mode, and then converted into CMYK mode image, the output film can be plated.
In the picture processing, if the picture that is opened for processing is itself an RGB mode picture, or the original picture is allowed to select the RGB mode for scanning using the scanner input process, this situation is better for the typesetting of the color newspaper. It is. When using Photoshop to scan the original image, the color image input through the scanner is the RGB mode image by selecting the RGB setting option in the color setting option in the file menu bar. In short, in the case where the picture mode is not required to be converted first, the picture in the RGB mode can be acquired, and the picture is processed in this mode, especially the picture downloaded from the Internet, in order to ensure the printing effect of the picture, it is necessary to Use RGB mode for processing. The discussion of the following aspects is very illustrative of this point.
(1) RGB mode is the color mode adopted by all optical principle based devices. For example, the display works in RGB mode. The RGB mode has a larger color range 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 the distortion of the picture color does not occur). This color is difficult to print when printing. This is also the main reason why the picture will be darker when converting the picture color mode from RGB to CMYK. When editing RGB mode images in Photoshop, you must first select the CMYK Preview command in the View menu (if you use Photoshop for Chinese, select the preview option in the view menu bar and select the CMYK option), that is, It is very important to edit the picture in RGB mode and display the picture in CMYK mode so that the color of the picture on the display screen that the operator sees is actually the color required for printing. This is very important when applied to printing. It is a good image processing method. When Photoshop works in CMYK mode, the color channel is one more than RGB. In addition, it uses the RGB display mode to simulate the CMYK display effect, and the CMYK operation method is completely different from the optical-based RGB principle. 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 images, some filters in Photoshop do not support CMYK mode. In addition, the editing process of images often goes through many subtle processes. For example, it may be necessary to combine the contents of several images. Since the original colors of the components cannot be the same, they need to be adjusted, or they may be Partially synthesized in some way, with filter processing and so on. Regardless of the effect of the image processing, the operator wants to produce and retain as many subtle effects as possible, and 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 processing images in RGB mode, a wider color space and more subtle editing effects will be obtained throughout the editing process, and most of these effects, if used well, can be preserved. Although it still has to be converted to CMYK mode and there will definitely be color loss, it is much better than losing the color of the picture 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 the color separation parameters will greatly affect the conversion of the image, and the Photoshop image processing software has the ability to control the color separation parameters. That is to say, when it is necessary to convert the image processed in the RGB mode into the CMYK mode for output, the color loss can be alleviated during the mode conversion by the adjustment of the color separation parameter 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. The RGB mode picture data information that has been corrected and corrected can be a valid document for long-term storage, so that RGB mode pictures retrieved from the archive in the future can be used 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 is system-level color management or image conversion in Photoshop.
(5) When using various printing machines, digital proofing equipment or calculator monitors for printing, proofing and outputting pictures, the main method of observing (and measuring) the difference in the color of the pictures reproduced by the above printing output devices is the measurement. The amount of cyan, magenta, and yellow required for sexual gray is printed as the gray balance of the replication system. If the image is converted to CMYK mode, then when reusing a different output device, the image requires adjusting the highlights, midtones, and shadows of the CMYK image, and changing the overall gray balance and color saturation. In order not to affect the quality of the picture print, the amount of black in the picture should be changed, but if the picture is printed without correcting the black data, a bad print result will result. For example, a CMYK mode image that was originally color-separated for a high-quality sheetfed press, if printed on a web press, would make the amount of black in the image larger, and the only way to deal with it is to correct the CMYK mode image. RGB mode pictures can use a larger RGB tonal range to reproduce brighter, more saturated colors. However, after the picture is color separated into CMYK, all pixels in the picture are within the CMYK tonal range.
As can be seen from the above discussion, the use of Photoshop to process color images should be done in RGB mode. However, it should be noted during the operation: pictures processed in RGB mode must ensure the authenticity of the picture color when outputting in CMYK mode; when processing pictures in RGB mode, be sure that the picture is completely processed before converting to CMYK mode picture. It is best to leave an image 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, while the CMYK mode is the color mode in which the pigment reflects light. The advantage of the Lab mode is that it compensates for the shortcomings of the first two color modes. RGB has too much excessive color between blue and green, and too much color between green and red. CMYK mode loses more colors in editing and processing pictures, and Lab mode has these aspects. Compensation. The Lab mode consists of three channels, the L channel represents brightness, which controls the brightness and contrast of the picture, and the a channel includes colors from dark green (low brightness value) to gray (middle brightness value) to bright pink (high brightness value). The b channel includes colors ranging from bright blue (low luminance value) to gray to focal yellow (high luminance value). The Lab mode is similar to the RGB mode, and the blending of colors produces a brighter color. Only the value of the luminance channel affects the light and dark variations of the color. The Lab mode can be thought of as a mode of RGB mode of two channels plus one luminance channel. Lab mode is device-independent and can be used to edit any image (including grayscale images) and is as fast as RGB mode, several times faster than CMYK mode. Lab mode ensures that there is no loss of color in the CMYK range when performing color mode conversion. If the RGB mode picture is converted to CMYK mode, an intermediate step should be added to the operation step, that is, first converted to Lab mode. In the non-color typesetting process, it is often used to convert pictures into grayscale images using Lab mode. For some pictures of the RGB mode downloaded on the Internet, if you do not use the Lab mode transition and then convert to grayscale, then sometimes you can't typeset the image when using the Founder Feiteng or Weiss typesetting software.
It can be seen that when editing and processing pictures, use Lab mode or RGB mode as much as possible, and then convert to CMYK mode when it is unavoidable. Once you turn into a CMYK mode image, don't switch back easily. If you really need it, switch to Lab mode to process the image. If the original picture used for scanning input is a color picture, but the picture is used in the grayscale layout, when inputting the picture with the scanner, do not input the original picture directly into the grayscale mode. The image should be input in RGB mode. After the RGB mode processes the picture, it is first converted into a picture of the Lab mode, and then through the channel separation command, the picture of the L channel is selected as the grayscale picture for printing.
Most operators are more straightforward in the process of actually processing the picture. What kind of picture is needed is directly scanned into the desired picture mode by the scanner, and then used for typesetting after a little processing, and looks like when printing. Still so. In fact, in order to really get a good picture printing effect, don't be afraid of trouble, follow the standard operating procedures.