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Printing Technology

Printing Technology. Xi’an University of Technology Prof. Dr.Cao Congjun. Cp5. Color & color reproduction. Fig.Visible range in the spectrum of electromagnetic waves. 为什么？. Why ？. Cp5. Color & color reproduction. For text and graphic. No problem. How to ？. Multi-color printing.

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Printing Technology

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  1. Printing Technology Xi’an University of Technology Prof. Dr.Cao Congjun

  2. Cp5. Color & color reproduction Fig.Visible range in the spectrum of electromagnetic waves

  3. 为什么？ Why？ Cp5. Color & color reproduction For text and graphic No problem

  4. How to？ Multi-color printing

  5. Autotypical multicolor printing (microscopic photo of a print image section); scale: cell spacing about 167 µm. aImage detail with homogeneous color (3-color print); bImage detail with structured color (4-color print)

  6. Color and Light Convex mirror prism 1. Color dispersion： White light White light 2. R / G / B basic optional colors： R 700nm G 546.7nm B 435.8nm- Additive primary color

  7. R R R Y Y M W G G B C 3.Additive color mixing process The building up of luminosity by means of the individual colors involved is known as additive color mixture.

  8. Additive mixing of different luminosity Light increasing?

  9. 4. Subtractive color：

  10. Subtractive color mixing： Absorb and Reflect Color

  11. Different chromatic value have a different absorptivity and reflectivity

  12. The same chromatic Different saturation

  13. fresco 5. C / M / Y subtractive primary colors photo

  14. C C C B B G K M M Y R 6. Subtractive color mixing processes With subtractive color mixing, luminosity发光度 decreases by the addition of individual colors.

  15. Color mixing with different percentage of ink Light reducing?

  16. Color separations and synthesization ? Color original Printing products The two basic condition of color reproduction: Color separations and synthesization

  17. Color separations： Color of original are separated to the basic ink color C film M film Color original Y film

  18. Color synthesization Ink the three primary color on each plate and overprint. Printing products

  19. Fig.Color separations and overprinting for reproduction in four-color offset printing

  20. 1. Color separations method： According to Subtractive color mixing principle, process the originals with scanner or camera to get c/m/y color separations. 滤色片 R filter — C negative film G filter — M negative film B filter — Y negative film

  21. How to Separate? Filter Incident light filter Transmission light Dye or Pigment

  22. originals filter M C Y negative film Y positive film Y inked plate Printing products 加色法色环图 减色法色环图 返回：颜色合成 返回：总结

  23. 2. Color synthesization methods • Copy separated color negative film to positive one • Platemaking • Inking plate separately with C/M/Y basic ink • Overprinting Dot overprinting

  24. Printing products

  25. Dot position relationship when overprinting: parataxis superposition(overlap) Did Superposition dot and parataxis dot have the same color result when overprinting?

  26. A. Superposition dot: Subtractive color mixing principle G R B K

  27. Dot superposition can faithfully reproduce color Note：the color result is influenced by the chroma, transparence, ink thickness, and overprinting order. purple blue

  28. (W) (W) B. Parataxis dot： R G

  29. (W) (W) (W) B. Parataxis dot： B gray

  30. Dot parataxis can reproduce color Note：the color result is influence by the chroma orange mauve

  31. (W) (W) Note! IF considering the dot size and the reflection form white paper , then … R The same color result R

  32. (W) (W) (W) (W) Note If considering the dot size the reflection from white paper , then… W K Gray Same color Gray Whatever dot superposition or parataxis in a unit area, the reproduction result are the same in the theory. Conclusion

  33. But Ideal model: C ,M ,Y three primary ink color In practice: we need to add a black plate because of material problem of ink and filter.

  34. Fig. Spectral distribution (degree of spectral reflection) of printing inks for multicolor printing -P102 Fig 5.6

  35. Color Masking Color masking has three distinct goals in color reproduction: ※To compress the density range of the color original (called tone correction) ※ To compensate for color deficiencies in process inks (called color correction) ※ To enhance the detail of the final reproduction (called sharpness enhancement)

  36. The ColorBlack Why black? Essentially, black is used in multicolor printing to reduced the technology expense of three chromatic colors to create black or gray value by the direct use of black ink, to cut down the use of expensive high-quality chromatic inks and also, primarily, in order to stabilize the printing process, that is, to make it less sensitive to variations in the individual colors.

  37. Black creation There are several methods for controlling the black color separation, that is, for supplement chromatic composition using the colors cyan, magenta, and yellow with the fourth color, black: Chromatic composition with Under Color Removal (UCR) Achromatic composition (or GCR: gray component reduction)

  38. Fig.Examples of determining the color separation for black using the multicolor printing of brown as an example. aChromatic composition; bChromatic composition with under color removal (UCR); c Achromatic composition (or GCR: gray component reduction); d Achromatic composition with chromatic color addition (UCA) Note: The chart serves to explain the principle and does not represent a metrologically accurate reproduction

  39. Chromatic Composition with Under Color Removal Under Color Removal (UCR) is a variant of chromatic composition, in which a part of the example there is to be a 30%UCR of the used brown. To this end ,the achromatic portion composed from cyan, magenta, and yellow is reduced from 70% by 30% and replaced by the corresponding black portion. As a result of this the area coverage is no longer 240%, but only 180% with the same apparent hue. This greatly simplifies the printer’s task , because the danger of offsetting is reduced and the color balance is easier to maintain.

  40. Achromatic composition Unlike chromatic composition, in achromatic composition in principle all achromatic portion are replaced by black (GCR: gray component replacement). Therefore, the blackening of chromatic color shades is no longer done by means of complementary color, but solely by black. The brown shown as example consists in achromatic composition of only magenta, yellow, and black. The area coverage is a total of only 100%. As a result of this, the color portion of cyan, magenta, and yellow can be noticeably reduced in all images and hues, the printing process becomes more stable, the ink acceptance (trapping) behavior noticeable improved.

  41. Summary Color originals Separation information Film Plate Color prints Color reproduction principles: Color separation and synthesization.

  42. Homework • P105 Review questions 4-8. • Describe the difference of UCR and GCR.

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