Sound Book For Children printing picture processing model discussion

Sound Book For Children printing picture processing model discussion

In the process of typesetting newspapers or magazines, we often encounter the processing of color pictures. When opening a certain color picture, it may be RGB mode or CMYK mode. When using Photoshop, should I use RGB mode or CMYK mode for color image processing? This article on this issue to talk about the author's view.

1. RGB and CMYK modes should not be ordinary

In the process of using Photoshop, first of all, you should pay attention to the fact that when you open an image, no matter it is CMYK mode or RGB mode, do not rotate between the two modes, let alone switch between the two modes. Because, in the image editing software, every time the color space of the image is converted, a part of the details of the original image will be lost. If an image is converted to RGB mode for a while and CMYK mode for a while, the information loss of the image will be very large. It should be said here that the picture mode used for plate printing in the process of color newspaper publishing must be the picture of CMYK mode, otherwise it will not be printed. But it does not mean that the printing effect of the picture processing in CMYK mode must be very good, or according to the situation. In fact, the effect of using Photoshop to select RGB mode is stronger than the effect of using CMYK mode, as long as the RGB mode after processing the picture, and then convert it to CMYK mode of the picture output film can be plate printing.

2. In order to ensure the printing effect of pictures, RGB mode must be used for processing

In the process of image processing, if the picture opened for processing is itself a picture of RGB mode, or the original picture is allowed to select RGB mode for scanning in the input process of scanner, this situation is the best for the typesetting of color newspaper. When using Photoshop to scan the original image, as long as you select the RGB setting option in the file menu bar, the color image input through the scanner will be in RGB mode. In a word, if you can get a picture in RGB mode without first converting the picture mode, you should use this mode to process the picture, especially if you download the picture from the Internet. In order to ensure the printing effect of the picture, you must use RGB mode for processing. The following aspects are discussed to illustrate this point of view.

(1) RGB mode is the color mode adopted by all optical devices. Monitors, for example, work in RGB mode. RGB mode has a larger color range than CMYK mode, so RGB mode can represent many colors, especially bright and bright colors (of course, the colors of the display must be corrected, so as not to distort the colors of the picture). This color is difficult to print. This is the main reason why the image darkens when you change the color mode from RGB to CMYK. When editing a picture in RGB mode in Photoshop, you must first select the CMYK Preview command in the View menu (if you are using Chinese version of Photoshop, select the preview option in the view menu bar and select the CMYK option). In other words, edit and process an image in RGB mode. The CMYK mode allows the operator to see the color of the picture on the display screen, which is actually the color needed for printing. This is very important, and it is a good image processing method when applied to printing. When Photoshop works in CMYK mode, it has one more color channel than RGB. In addition, it also uses the display mode of RGB to simulate the display effect of CMYK. Moreover, the calculation mode of CMYK is completely different from the principle of optic-based RGB, so the efficiency of processing pictures in CMYK mode is lower. The quality of the processed images is also less.

(2) Some filters in Photoshop do not support CMYK mode when processing images in Photoshop. In addition, the editing and processing of pictures often have to go through many subtle processes, such as the content of several pictures may be combined together, because the original tone of each component can not be the same, need to adjust them, may also make each part in a certain way, and filter processing and so on. No matter what effect a picture is processed to achieve, the operator wants to produce and retain as many subtle effects as possible, and make the picture as real and rich in detail as possible. Because RGB mode has a much larger color range than CMYK mode, therefore, in the entire editing process of an image processed in RGB mode, You'll get wider color Spaces and more subtle and varied editing effects, which, if used well, can mostly be retained. You'll still have to switch to CMYK eventually and you'll definitely lose color, but it's better than losing color in the first place.

(3) When converting RGB mode images to CMYK mode images, color separation parameters will play a decisive role in the effect of image conversion. The adjustment of color separation parameters will greatly affect the image conversion, Photoshop image processing software has the ability to control the color separation parameters. That is to say, when the image processed in RGB mode needs to be converted into CMYK mode for output, the color loss in the image mode conversion can be reduced by adjusting the color separation parameters in the conversion process.

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

(5) In the use of a variety of printing presses, digital proofing equipment or computer monitor for picture printing, proofing, output, the main way to observe (and measure) the color difference of the picture copied by the above printing output equipment is to measure the amount of blue, magenta and yellow required to produce neutral gray, printing is called the gray balance of the reproduction system. If the image is converted to CMYK mode, then reusing a different output device requires adjusting the highlights, middle and dark points of the CMYK image, as well as changing the overall 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 if the picture is printed without correcting the black data, it will produce bad printing results. For example, a CMYK pattern image, which was originally a high quality sheet press color separation, will have too much black in the image if printed on a web press. The only way to do this is to correct the CMYK pattern image. RGB mode pictures, on the other hand, can use a wider range of RGB tones to produce brighter, more saturated colors. However, after the picture is separated to CMYK, all pixels in the picture are within the CMYK tone range.

From the above discussion, it can be seen that the RGB mode should be used as far as possible when using Photoshop to process color pictures. However, in the process of operation, attention should be paid to the pictures processed in RGB mode to ensure the authenticity of the picture color when output in CMYK mode; When using RGB mode to process an image, make sure the image is fully processed before converting it to CMYK mode. It is best to keep an RGB mode image as a spare.

3.Photoshop's Lab color mode also has good features

In addition to processing images in RGB mode, Photoshop's Lab color mode also has good features. RGB mode is based on the principle of optics, while CMYK mode is the color mode in which the pigment reflects light. The advantage of Lab mode is that it makes up for the shortcomings of the previous two color modes. RGB has too many overcolors between blue and green, and too little between green and red. CMYK mode loses more colors in the process of editing and processing pictures, while 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 a channel includes colors from dark green (low brightness value) to gray (medium brightness value) to bright pink (high brightness value), and the b channel includes colors from bright blue (low brightness value) to gray to burnt yellow (high brightness value). Lab mode is similar to RGB mode in that the mixing of colors will produce brighter colors. Only the value of the luminance channel affects the shading of the color. The Lab mode can be regarded as the RGB mode of two channels plus a brightness channel mode. Lab mode is device-independent and can be used to edit and process any image (including grayscale images) as fast as RGB mode and several times faster than CMYK mode. Lab mode ensures no loss of color in the CMYK range during color mode conversion. If the RGB mode image is converted to CMYK mode, an intermediate step should be added in the operation step, that is, the first conversion to Lab mode. In the process of non - color typesetting, the Lab mode is often used to convert the picture into gray. For some RGB mode pictures downloaded from the Internet, if the Lab mode is not converted into gray, then sometimes it is not possible to typeset the pictures when using Founder Feiten or Vith typesetting software.

Thus, when editing and processing pictures, try to use Lab mode or RGB mode first, and only switch to CMYK mode when you have to. Once the image is transferred to CMYK mode, do not easily transfer back, if necessary, 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 for gray layout, do not input the original picture directly into gray mode when the image is input by scanner, the image should be input in RGB mode. After processing the picture in RGB mode, it is first converted into a picture in Lab mode, and then through the channel separation command. The image of L channel is selected as the grayscale image for printing.

Most operators in the actual process of processing pictures, are relatively straightforward, what kind of pictures need to be directly scanned into the required picture pattern with the scanner, and then a little processing is used for typesetting, printing looks the same thing. In fact, in order to really get a good picture printing effect or do not be afraid of trouble, according to the standard operation steps.