VARIABLE DOT OPTIMIZATION
Our variable dot optimization technology optimizes variable dot use on inkjet printers that support variable droplet printing, for virtually any ink/media combination across all suitable (and available) print resolutions and print modes. It is able to identify the optimum variable dot family on printers that offer multiple variable droplet combinations, best suited to the desired print resolution; and, can determine which print resolutions may be unsuitable to any available dot family. The algorithms are able to determine the best ratio of dot sizes to produce a linear output with optimum dynamic range. It has been used extensively with two-bit variable droplet printers, including printers with multiple dot families, and can automatically exclude dot sizes not suitable for a given resolution (including selecting a fixed dot size instead of variable dot when fixed dot would provide a greater dynamic range and better overall print quality).
In this example, the target density calculation is made first at 720x720 dpi using the smallest dot family, then 720x720 with the next largest, and so on until the optimum family is identified; if none of these achieve optimum target density, the procedure continues at 720x1440, etc. At some point, the optimum density will be identified.
|
|
The variable dot optimization utility creates a variable dot lookup table (VLUT) by first determining the amount of ink necessary to saturate the media (dot density and drop volume) for each primary ink color. It does this automatically, using a custom-designed variable dot calibration chart and spectrophotometer (or colorimeter), beginning with the lowest desired print resolution and working up to higher print resolutions. After each chart is measured, the utility analyzes the results to determine the best course of action: switch variable dot family; constrain print resolution; print with fixed dot; or, proceed to the next resolution setting. On printers with an integrated (on-printer) multi-spectral color sensor (spectrophotometer or colorimeter) this process can proceed automatically with virtually no operator interaction.
VARIABLE DOT LOOKUP TABLE
The utility processes each chart until it is able to identify an optimum variable dot family for each suitable resolution; in some cases it may not use all of the dots available in a particular family, or it may opt for a single (fixed) dot size. It may also recommend rejecting a resolution because maximum density cannot be achieved with any dot family, or because maximum density is achieved too quickly. All of this is accomplished with minimal operator intervention (other than performing instrument measurements if that is not done on printer). As a result, the user does not need to understand the intricacies of variable dot use or how variable dot impacts image quality and dynamic range. Variable dot is optimized for print resolution and media dot gain. Once this is completed, no further linearization is necessary, although the printer can be still G7 calibrated.
To create the VLUT, the small and medium droplet curves are projected onto the large droplet curve to determine the relative droplet size of each. This data is then passed to the VLUT tuning widget; this is where the actual variable dot curves are calculated, so that optimum dynamic range can be achieved for each print resolution. The VLUT tuning widget can also be used to adjust the variable dot ratios to account for dot gain change due to changes in ink, media or environment; it can also be used to manually tweak the variable dot curves to account for printer and media-induced artifacts such as banding and mottling.
To create the VLUT, the small and medium droplet curves are projected onto the large droplet curve to determine the relative droplet size of each. This data is then passed to the VLUT tuning widget; this is where the actual variable dot curves are calculated, so that optimum dynamic range can be achieved for each print resolution. The VLUT tuning widget can also be used to adjust the variable dot ratios to account for dot gain change due to changes in ink, media or environment; it can also be used to manually tweak the variable dot curves to account for printer and media-induced artifacts such as banding and mottling.
