Analysis Of Color Mode Conversion Of White Paperboard Paper Tube Prepress Manuscript

Analysis of color mode conversion of White Paperboard Paper Tube prepress manuscript

In the design of print manuscript, no matter what color mode is used in the pre-production, the final color mode is usually bitmap, grayscale and CMYK mode (spot color channel color mode is special, its color gamut is relatively large). Therefore, color mode conversion is particularly important in the prepress production process. (PhotoShop CS software is taken as an example in this paper)

1 Switch from RGB mode to CMYK mode

Open an RGB image in Photoshop. When we click on the menu "View \ gamut Warning", grey appears in the pattern. In the process of converting RGB to CMYK, the color gamut of RGB is larger than that of CMYK, which may cause color overflow in the image, resulting in color loss. The gray part is the color overflow range in the image.

So, if you define the color mode to be CMYK when building a new file, so that all the colors are in the CMYK gamgamet, there will be no color overflow. However, in CMYK mode, Photoshop has a lot of effects, filters, and can't be used for some special cases of color separation. Therefore, in the early stage of the production of print design, the image is best to use RGB mode, so as to facilitate our adjustment and processing. Until the entire design draft is basically completed, then transfer to CMYK. Let a variety of color patterns for our design and production to play its maximum effect.

2 Color mode to gray mode

Compared with RGB to CMYK, there are more methods for color to gray level, but different operation methods are also different for the final gray level presentation.

1) Color RGB or CMYK images directly into gray mode. The most common way to do this is to go directly to the Photoshop menu "Image, Mode, Grayscale", which does not take into account any image conditions. The whole gray image after conversion is darker, so it is necessary to improve the brightness of the middle tone by adjusting the curve or the color level.

2) Use channel mixers. Open the "Image/Adjustment/Channel mixer", select a single color, and then adjust the corresponding source channel value, adjust the gray level you need.

3) Turn to gray after removing the color. First, the RGB image is de-colored so that it is displayed in gray level and all color information is neutral. Then switch to grayscale mode.

4) After switching to Lab mode, take out L brightness channel as gray level map. First, switch RGB to Lab mode and check the Lab channel. Channel a and channel b are deleted and only channel L is retained. At this time, channel L becomes channel Alpha1. At this time, we can click "image mode" to see that it is multi-channel mode, and then convert the multi-channel mode into gray mode, and obtain gray pattern from L channel in Lab mode.

5) In the channel panel, select a relatively clean channel whose gray value meets the requirements to get the gray map. I can make a copy by clicking channels R, G and B respectively in the channels panel, selecting a more suitable channel and copying it. Then, channels R, G and B are deleted. After deletion, click "Image mode" to turn the multi-channel mode into gray mode.

Through the gray pattern obtained by the above 5 methods, we view them respectively through the histogram.

We can see that the grayscale images obtained by methods 2) and 4) are relatively full in level and soft in image. The grayscale images obtained by the other three methods all need to use a series of adjustments such as color levels and curves to get a more delicate image texture.