### 5.8. Trame d’imprimerie

#### 5.8.1. Généralités

Figure 17.74. Exemple d’application du filtre Trame d’imprimerie

Image d’origine

Filter « Newsprint » applied using RGB color mode, PSSquare pattern for all channels, red period 6, green period 8, blue period 10, angle 15 for all channels.

This filter performs digital halftoning with optional modulations. Halftoning is the process of rendering an image with multiple levels of gray or color (i.e. a continuous tone image) on a device with fewer tones; often a bi-level device such as a printer or typesetter. Be aware that Newsprint is not a filter for generating half-tone screens for print, but for simulating the appearance of printing with them.

Le principe de base est d’échanger la résolution contre une plus grande profondeur de couleur.

Plusieurs approches sont possibles, la plus simple étant de rejeter les bits d’information de ton de poids faible. Malheureusement, les résultats ne sont pas très bons. Mais il n’y a aucune perte de résolution spatiale.

Imagine a grid super-imposed on the original image. The image is divided into cells by the grid - each cell will ultimately hold a single spot made up of multiple output pixels in order to approximate the darkness of the original image in that cell. Obviously, a large cell size results in a heavy loss in resolution!

#### 5.8.2. Activating the Filter

This filter is found in the main menu under Filters → Distorts → Newsprint….

#### 5.8.3. Options

Figure 17.75. Options du filtre « Trame d’imprimerie »

Presets, « Input Type », Rognage, Blending Options, Aperçu, Merge filter, Split view

  | Note
  Ces options sont décrites dans Section 2, « Options communes ».

Channels

  This group controls the channels to use and the settings for each channel.

  Color Model

    Select which color inks to use: White on Black, Black on White, RGB, or CMYK.

  For each color ink or channel

    Settings that can be changed for each color ink or channel are listed here.

    Motif

      Select the halftoning pattern to use. Choices are Line, Circle, Diamond,, PSSquare (or Euclidean) dot, Crossing Lines.

    Période

      The number of pixels across one repetition of a base pattern at base resolution.

    Angle

      The grid angle that should be used. This angle can be adjusted with the slider, number entry, or using the angle control by moving the arrow in the circle.

    Black pullout

      This setting is only available when CMYK was chosen as Color Model and the selected channel is Black. It regulates how much of common gray to pull out of CMY.

  Lock patterns, Lock periods, Lock angles

    These three check boxes, if enabled, lock the settings mentioned above to be the same for all channels. If disabled, then these settings can be set individually for each channel.

Quality
  Anti-alias oversampling factor

    This sets the number of samples that are averaged for anti-aliasing the result.

    Proper halftoning does not need anti-aliasing: the aim is to reduce the color depth after all! However, since this filter is mainly for special effects, the results are displayed on screen instead of on a printer. So it is often useful to apply a little anti-aliasing to simulate ink smearing on paper. If you do want to print the resulting image then set the anti-aliasing to 1 (i.e., off).

Effects
  Turbulence

    Color saturation dependent compression of period.

  Blocksize

    Number of periods per tile. This tiling avoids high frequency anomalies that angle boost causes.

  Angle Boost

    Multiplication factor for the desired rotation of the local space for the texture. The way this is computed makes it weak for desaturated colors and possibly stronger where there is color.

5.7. Mosaïque |  | 5.9. Coordonnées polaires

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