Re: Printing gradients with 2 Pantone colors
Why not just move the 2 centers of each gradients toward their respective zero points to make the gradient darker in the middle?
*On the banding problem*: this is a mathematical formula from adobe:
Creating smooth gradients for PostScript output 12/3/07 10:29 AM
http://kb.adobe.com/selfservice/viewContent.do?externalId=tn_3668&sliceId=2 Page 1 of 5
ID: tn_3668
Products affected
FreeHand
Adobe
TechNote
Creating smooth gradients for PostScript output
Issue
Sometimes when I print graduated fills from FreeHand I get large bands of
color, not smooth gradations.
Reason
Postscript actually creates gradations of color by combining small areas of
single color. In most print output these bands of color are so small that your
eye blends them together. But sometimes Postscript can cause these
bands if it does not have the correct information. However, there are steps
which you can take to reduce the bands so the gradation seems smooth.
Solutions
The simplest solution is to set File/Output Options/Maximum Color Steps to
256.
Further Information
It is possible to calculate the size of tint bands in a gradient (i.e., gradient
fill, whether radial, linear or logarithmic) to predetermine banding and
assure efficient gradients for PostScript output.
A correct understanding of the mathematics involved in creating smooth
gradients will provide the tools for producing the desired effect without
compromising quality.
A. Creating Gradations Digitally
B. Formula for Calculating Tint Bands in Gradients
C. Determining the Available Number of Tints& Band Size
D. Working with Process Colors
TechNote Details
Did this resolve your
problem?
Yes
No
300 characters
Send
Take a Survey
Take a survey about
Adobe's resources for
learning and problem
solving.
Type feedback here
Creating smooth gradients for PostScript output 12/3/07 10:29 AM
http://kb.adobe.com/selfservice/viewContent.do?externalId=tn_3668&sliceId=2 Page 2 of 5
E. Adjusting Known Variables to Reduce Banding
F. General Tips
A. Creating Gradients Digitally
Banding is a result of producing halftones digitally. It is possible to calculate
the band widths before imaging. These calculations will aid in creating
efficient gradients with the optimum number of steps to prevent noticeable
banding and optimize imaging time.
The results of the calculation will provide:
1. How many different tints the printer can print.
2. What range of those tints the color change can use.
3. Whether the resulting tint bands are fine enough to create the illusion
of a smooth gradient.
The following information is needed to calculate tint band widths:
1. The printer resolution in dots per inch (dpi).
2. The screen ruling in lines per inch (lpi).
3. The change in color between the beginning and ending tints in the
gradient described as a percentage.
4. The physical distance between the beginning and ending tints of the
gradient described in points.
B. Formula for Calculating Tint Bands in Gradients:
([Resolution(dpi)]/[Screen Ruling(lpi)] [Squared] +
1= [a]
Example:
A printer with a dpi of 600 printing a file with a Screen Ruling set at 85 lpi
would yield this equation:
600/85= 7.0588 (round off to 7) 7 squared= 49 + 1 =
50 [a] = initial number of tints available to be printed.
[a] x [amount of tint change in gradient] =
Example:
An object in FreeHand has a gradient set that starts at 90% black and ends
at 10% black. The change in the tint is 80%, and would yield this equation:
50 x 80% (or .8) = 40
Creating smooth gradients for PostScript output 12/3/07 10:29 AM
http://kb.adobe.com/selfservice/viewContent.do?externalId=tn_3668&sliceId=2 Page 3 of 5
is the actual number of tints available in the current tint change.
[length of the area to be filled] / = [c]
Example:
The object in FreeHand is a horizontal rectangle 4 inches wide (288 points)
by 1 inch (72 points) high, and the gradient fill above is applied at an angle
of 0 degrees (the fill is horizontal over the 4 inch distance) would yield this
equation:
288 / 40= 7.2
[c] is the size in points of each band, or how visible banding will be and the
minimum width of objects used to create the gradient.
C. Determining the Available Number of Tints & Band Size
The first part of the calculation determines exactly how many different tints
the printer can produce at the screen ruling chosen. A certain tint is based
on the size of the halftone dot the printer creates, which in turn is based on
the combination of printer resolution and screen ruling chosen. The higher
the resolution of the printer, the more tints it can potentially create.
1. Divide the printer resolution by the screen ruling chosen in setting up
the PPD.
2. Square the integer value (discard the remainder or decimal), then add
1 to the result. This is the approximate number of tints the printer is
capable of producing with these two variables.
3. If the number calculated for the initial number of tints available is
higher than 256, reduce that number to 256 because the PostScript
Level 1 graphics language cannot create more than 256 different tints
per ink. (Some PostScript Level 2 devices may allow more than 256
tints per ink.)
([Resolution (dpi)]/[Screen Ruling (lpi)])[Squared]+1 = [initial number
of tints available]
For example:
If printing a job at 150 lines per inch (lpi) at 1270 dots per inch (dpi),
this formula yields roughly 72 different tints available. If the resolution
is raised to 2540 dpi, then 287 different tints are available, but since
PostScript Level 1 is only capable of 256 tints, the number 256 must
be used.
4. Calculate the percentage of available grays or the actual number of
tints available.
Express the "percent change between start and end" as a decimal
(e.g., if the gradient goes from 20% to 80%, the tint change is 60% or
Creating smooth gradients for PostScript output 12/3/07 10:29 AM
http://kb.adobe.com/selfservice/viewContent.do?externalId=tn_3668&sliceId=2 Page 4 of 5
(e.g., if the gradient goes from 20% to 80%, the tint change is 60% or
.6).
[Initial number of tints available] x [amount of
tint change in gradient] = [actual number of
tints available]
Note: This step is necessary because a tint change of less than 100%
uses less than 100% of the total available range of tints (e.g., 60% of
256 tints, or 153 tints).
5. Measure the object in the direction of the gradient and convert that
length into points (there are 72 points in an inch).
6. Divide the length by the actual number of tints available to determine
the size of each tint band. This number reflects the exact width of any
banding that might occur in the gradient, and is the minimum width of
objects used to create the gradient.
[length of area to be filled]/[actual number of
tints available] = [size of each tint band]
For example: If the fill is 4 inches (or 288 points) long and has 153
tints available, then each tint band will about 1.9 points wide. If the
calculation specifies the band size at less than 1 point wide, banding
will not be visible. If between 1 and 2 points, this is adequate for most
circumstances. If over 2 points, it is up to the discretion of the
designer as to whether the quality will be suitable for the type of work
produced. In most cases, as long as there are 256 total tints
available, the human eye is less likely to perceive any banding once
the final work is printed.
When predetermining banding that may occur in process color
gradations, it is important to remember that four separate inks are
involved, each having its own degree of banding. It is best to
calculate banding for the ink that has the most change in color, and
the ink with the least change. This gives the complete spectrum of
what banding to expect. Just run the color change in each ink through
the formula above.
Heavy banding in a lighter color (i.e., yellow) will be less evident when
the final product is printed than banding in a darker color (i.e., black).
E. Adjusting Known Variables to Reduce Banding
The variables that effect banding are the four numbers needed to
predetermine banding: the device resolution, screen ruling, tint change in
the gradient, and the length of the gradient.
To adjust a gradient that is banding:
Creating smooth gradients for PostScript output 12/3/07 10:29 AM
http://kb.adobe.com/selfservice/viewContent.do?externalId=tn_3668&sliceId=2 Page 5 of 5
1. Determine the variables that can be altered:
a. Are 256 tints already available from the first equation? Raising
resolution or lowering screen ruling after passing 256 tints is
pointless because PostScript Level 1 can only produce 256 tints
per ink. If the 256 limit has already been reached, adjust the
remaining variables.
b. Does the nature of the job dictate a strict requirement for screen
ruling? If it cannot be changed, adjust other variables.
c. Adjust the remaining variables, adjusting first the variables that
have the least effect on the visual composition.
2. Adjusting variables to reduce banding:
a. Raise the resolution. Raise until the formula shows the gray bands
are fine enough or until the number of initially available grays
passes 256.
b. Lower the screen ruling. Lower the screen ruling value until the
formula shows the bands are fine enough or until the number of
initially available tints passes 256
c. Increase the difference between the starting and ending tints in the
gradient.
d. Decrease the length of the gradient.
F. General Tips
Do not throw in extra gradient steps to create a smoother effect. The
number of tints produced is related to the results of this formula. Enter only
the number of steps needed to match that result. Specifying a number
significantly more than the available tints is extra information that the printer
cannot use but still has to process (RIP), making the print time considerably
longer with no increase in quality.
TechNote Details
Last Update: 07-06-2006
ID: tn_3668
Permanent Link: http://www.adobe.com/go/tn_3668
Products Affected:
FreeHand