Image Dither

No shading

Any difference between input and output color is ignored. This may easily result in "color banding".

 

Error diffusion

This is the default. Color differences are distributed to the neighboring pixels. Normally, this results in a substantially better color rendering, although at the expense of image details; the sharpness becomes slightly degraded.

No shading	Error difussion

Print

The information provided below applies to the UNIX versions of EasyCopy.

When an image is printed on a printer which can truly reproduce color intensities (dye sublimation printer) the methods described above for Display and Save apply.

On any other printer color intensities are simulated by dot patterns. EasyCopy supports different Shading Methods:

No shading

This is the fastest shading method; it includes only a threshold operation for each pixel: if the intensity of a primary color is greater than 50% the dot is set, otherwise it is not. The method is only recommended for draft output.

 

Intensity

The intensity distribution method uses error diffusion to record and accumulate the intensity errors introduced by threshold operations for one dot and compensates for the error by distributing it to the neighbors.

Intensity distribution is recommended for printing photographic images on ink jet printers and laser printers; it can often give a better photo-realistic rendering than screening.

 

Scatter

This is a proprietary improved error diffusion method in which the placement of each pixel used to compensate for correct intensity is calculated from a detailed analysis of all pixels in the neighborhood.

This method is recommended for superb reproduction of photographic images. It is, however, not available for all printers.

Dithering

Select Dithering to get a dispersed dither shading method: Color intensities are rendered by means of dither patterns built from dither cells in which the active dots are distributed evenly over the area to be shaded:

Dither shading is available for 2x2, 3x3, 4x4, 6x6, and 8x8 dither cells. The cell size determines the number of distinct intensity levels that can be rendered and represents the tradeoff between sharpness and color depth; the optimal choice depends on the image contents.

Dither shading is recommended for printers if the dot size is approximately the same as the dot distance. However, the dot size is often larger than the dot distance; twice the dot distance is not unusual for high resolution printers. In these cases dither shading results in excessive color saturation:

All intensities above ~0.3 give full coverage in this example, so avoid dither shading when the dots are greater than the distance between dots.

The specified resolution of a printer reflects how accurate a dot can be positioned on the media, that is, it refers to the dot distance rather than the dot size.

Halftoning

This method is also known as clustered dither. Color intensities are rendered by means of dither patterns built from dither cells in which the active dots are clustered as closely as possible over the area to be shaded:

Halftone shading is available for 2x2, 3x3, 4x4, 6x6, and 8x8 dither cells. The cell size determines the number of distinct intensity levels that can be rendered and represents the tradeoff between sharpness and color depth; the optimal choice depends on the image contents.

Halftone shading is recommended for printing drawings and diagrams on printers with high resolution. The method overcomes the problem of dots being larger than the dot distance that was mentioned for dither shading.

For low resolution the result of halftoning is a visible raster imposed on the image, and dither shading is then a better choice.

For photographic images the method can result in unpleasant interferences (moiré patterns), because all primary colors are rendered using the same grid of dither cells.

 

Screening

This method employs rotated clustered dither cells (halftones). By using different screen angles for each primary color this method avoids moiré patterns. It is therefore well suited for photographic images on high-resolution printers.

The cell sizes offered by EasyCopy for screening are known as 4x4 and 6x6. However, these figures are not to be taken literally, they are used for convenience and express the nearest halftoning equivalent. The true cell size is more complex. In order to get correct tiling several unit cells are used to compose a macro cell. The unit cell dimension is not as simple as, say, 6x6; in the example shown below the side of the unit cell is non-integral, namely = 6.7 pixels.

 

Hardware

Some printers have built-in support for color rendering. If you use a hardware based Shading Method a hardware based Scaling Method must also be used.