........Inside of Dot-Proofing Technology


Inside of Dot-Proofing Technology

Dot-proofing Technology is NOT A MAGIC
In the basic theory of Dot proofing can be regarded as softening the real dots for inkjet spots moderately.
You can imagine the situation in designing small desktop icon image.

Under the limitation of pixels, we need to add diluted color to soften the edges and smooth curves.
We do the similar work so called anti-aliasing for designing fonts.
If we do not soften the image in the unit cell when creating dot-proofing image, we¡¯ll lose the original shape of dots and that might generate strange moire-look patterns in result, which will not be shown in the final press output.
It is very important to understand that ¡°the hardest or sharpest dot¡± which people easily expects from dot-proof is not always good for dot-proof itself. The sharpness or hardness of dots should be optimized to a certain level, enough to predict the moire in final press. Each dot need not as that sharp as real press output.

Understanding Basic Concept of Dot-proofing
It is better to explain the real processes of dot-proofing technology, to understand what we can exactly expect from dot-proofing, because it is not a magic.

Let¡¯s say that we have C, M, Y, K images in 1 bit TIFF, in 150 lpi at 2400 dpi for the press print.
A close look of 50% Cyan area in the image will have 16 by 16 pixels per cell to generate 257 level of gradation.

For inkjet printing, we need to down-sample the image into lower resolution, e.g. 720 dpi.
In this case, we have approximately only 5 by 5 (actually 4.8) pixels in a cell. This means we have only about 25 points per cell where we can drop the inkjet spot.
Under the continuous color proofing, only 50% cyan information will be contained in the cell with ignoring the screen dots and the proof print output with inkjet spots will be like the below image.

For dot-proofing under the same condition of continuous color proofing, we need to mimic the hard dots of original image under high resolution into the limited pixels of lower resolution cell.
However, when we use 8 bit gradation per each color instead of 1 bit, we can get similar shape of dots under the limited numbers of pixels.

* We have recommended value of sharpness
but users can adjust the sharpness for different condition
to each different image and printing environment.

In the stage of dropping the droplet of inkjet proofer, there could be different results due to each different option which user can select. We recommend to use supercell technology of Epson, which is using the smallest droplets. Or you can use variable dots of Epson, HP and Canon. You can also use light colors to add more dots, but this may make the colors of proof different from press. In summary, you need to use supercell/variable dot option, together with light colors if possible. In this case, you are recommended to set 'screen' option as 'none' (If there's no option to ignore the screen, you can select ¡®error diffusion¡¯), and you should not use 'anti-aliasing' option, which can distort the screen dots.


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