How to perform correct RGB-CMYK data conversion?

1.RGB data processing
The so-called RGB data processing refers to the use of RGB data as a prepress worker's data, and the data is converted to meet the CMYK printing data. Specifically include:

(1) CMYK conversion operation of RGB data;

(2) Calibration operations (digital cameras, displays, output devices, storage media, etc.);

(3) Image processing operations (color correction, image synthesis, tone conversion, image correction, etc.);

(4) Color management (prediction of output results based on digital data, etc.), etc.

In order to do RGB processing, photographers, designers, plate-making companies, etc. are required to distinguish their respective responsibilities, and RGB data processing standards are formulated accordingly. It is important to clarify the conversion rules.

Prepress companies should set up departments to inspect incoming RGB digital manuscripts in order to transfer the appropriate data to the next process as required.

2. The necessity of RGB workflow

In order to realize the processing of RGB data, it is necessary to structure the workflow corresponding to RGB image data. Now that the number of RGB originals for digital cameras has increased, it is necessary to meet this demand.

Through the implementation of the RGB workflow, the responsibility and workload of photographers, designers, etc. can be reduced, and the occurrence of quality accidents can be reduced. In addition, the delivery period can be shortened and the cost can be reduced. If the image data is made into a database, in addition to improving the work efficiency, the image data can be used again.

3. Benchmarking of RGB Workflow

In order to construct an RGB workflow, it is necessary to provide the cooperation of the employer of the manuscript. Therefore, it is important to propose a standard. The following are specific examples.

(1) Requirements for photographers

* Use photoshop 6.0 or later;

* The display must be calibrated;

* Do not convert RGB image data to CMYK data;

* If you need to make major changes to the color, please submit it to prepress company in RAW data format;

* Set the resolution of the image to 350dpi;

* Provide data content records (photographer, use software, color space, resolution, sharpening, etc.);

* When the printing size is A4 size, use a camera with 6 million or more pixels;

* For prints with high quality requirements such as skin photography, photography with a camera number of 12 million or more is required.

(2) Requirements for designers

* The monitor must be calibrated;

* Do not convert RGB image data to CMYK data;

* The color correction and color management of the image are sent to the prepress company;

* The layout of the continuous spelling, layout, etc. was passed to the prepress company.

4. Professional perspective of CMYK conversion

For CMYK conversion, the color settings made according to the graphic must be changed. The conversion job itself is very simple and originally meant to "reproduce the desired color, how to convert to obtain high quality", but this is a professional technical problem. In order to reproduce the colors approaching the RGB image, density adjustment and gradation adjustment are required, and techniques are applied in the CMYK color space to obtain the desired color. Here are some key points for obtaining high-quality color reproduction:

(1) At the same time as adjusting the generation of black prints, it is possible to perform conversion operations (make it possible to print clear black text, adjust gray balance, approach original colors, pursue details, etc.);

(2) Because the problem of inaccurate printing plates sometimes occurs, trapping is performed (makes the background less visible). In the case where the image data or the background of the second point has a level, it is quite difficult to prevent the printing plate from being inaccurate, and a skillful technique is needed. This kind of work can be said to be a professional job.