Trap
The parameters relating to "Trap" allow a general control of the trapping conditions. The following three conditions must be met in order to create a trap:
1.absolute difference between separations
The difference in dot percentage between two colors must be greater than 5% in at least two separations.
2.relative difference between separations
The difference between two separations relative to the lighter of the two must be greater than the step limit entered by the user.
3.Overall common density
The sum of the neutral density of all separations must be less than the common density limit.
This parameter indicates the degree to which the separations of adjacent colors must vary before a trap is created.
A trap is created in those separations where the difference between adjacent colors is greater than the input value.
How this works:
•Lower values cause traps to be created even with slight differences in color. Accordingly, there are a greater number of traps.
•Higher values mean that traps are created only if the differences in color are greater. Accordingly, there are not as many traps.
|
Note: There is no trapping if the difference between abutting colors is less than 5 %. |
Example:
The step limit ranges from 1% to 100%. The default value is 25%.
Colors C60M10% and C50M70% are adjacent.
An input value of 25% means: 25% of the density of the lighter of the separations is added to it:
C50% + 25% = C62.5%
M10% + 25% = M12.5%
If the darker color is still darker afterwards, trapping is performed.
C60% is not darker than C62,5%. This separation is not trapped.
M70% is still darker than M12.5%. This separation is trapped.
This "Common Density Limit" is used to prevent traps being created in places where flashes are not visible due to the ink recipe. Any spot colors will also be taken into account.
How this works:
•Lower values mean that traps are not created if there are only slight differences in color. Accordingly, there are not as many traps.
•Higher values mean that traps are created only if there are greater differences in color. Accordingly, there are a greater number of traps.
The values for the "Common Density Limit" range from 0 to 10. The default value is 0.5.
Example:
"Common Density Limit" = 0.5, this means a trap is not to be created if the common neutral density is greater than 0.5.
Color 1 -> 60% cyan and 20% magenta
Color 2 -> 40% cyan and 70% magenta
The neutral density value (ND) of cyan is 0.61, that of magenta 0.76.
Formula for calculating neutral density (ND):
|
ND = -1.7 * log (1 - color * (1 - 10 (-0.6 * D) ) ) |
Result: ND= 0.294 common neutral density
The common neutral density of both colors is less than the specified Common Density Limit. In this case, a trap is created.
The "Centerline Trap Limit" specifies under what conditions a centerline trap will be created.
The default trap direction (lighter color moves under darker color) is not obligatory between colors with a similar neutral density (ND).
The default value is 100% and means that no centerline trap will be created.
Rare exception: Centerline traps will be created if the neutral density of the objects is identical.
How this works:
•Max. value 100%: None of the created traps are "centerline".
Rare exception: Centerline traps will be created if the neutral density of the objects is identical.
•High value: A few of the created traps are "centerline".
•Low value: Many of the created traps are "centerline".
•Min. value 0%: Almost all of the created traps are "centerline".
Theory:
A centerline trap is created if the neutral density of the lighter color is greater than the neutral density of the darker color multiplied by the "Centerline Trap Limit".
The values for "Centerline Trap Limit" range between 0% and 100%.
Example:
A color with a neutral density of 0.9 and a color with a neutral density of 1.0 are adjacent. Input value = 80%.
If 80% neutral density of the darker color is lighter than the neutral density of the lighter color, then the created trap is "centerline".
"Trap Color Scaling" helps to make traps less noticeable (for example, in pastels).
The default value is 100% and means that there is no trap color scaling.
How this works:
•The lower the "Trap Color Scaling" entered, the lighter the trap colors and consequently the less visible the traps.
Theory:
"Trap Color Scaling" makes traps less visible by reducing the various separation colors according to their trap color percentage. Trap Color Scaling only affects those parts of the trap color that originate from the lighter of the adjacent colors.
The values for Trap Color Scaling range between 0% and 100%.
Example of a trap color reduction:
Trap Color Scaling = 75%
The yellow separation in the darker color is 60%.
The yellow separation in the lighter color is 88%.
Without a color reduction, the trap in the yellow separation would be 88%. With Trap Color Scaling, the difference (88 - 60 = 28) is now reduced by 75% (0.75 * 28 = 21) and this 21% is added to the separation with the lesser value (60 + 21=81).
Result:
By means of a 75% Trap Color Scaling, the trap color in the yellow separation was reduced from 88% to 81%.
Objects lying on top that have 0% in all separations are spread against color objects lying below that have color in more than one separation. The darkest separation, measured against neutral density, of the object lying below is kept. As a result, for example, white text on a red background is spread but red text on a white background is not choked.
This is a trapping function that is required especially in some packaging jobs.
With this function enabled, the brighter separations are pulled into the brighter object instead of the darker separations being pulled into the darker object during trap generation. This usually creates a white frame around every object.
This "White Framing" is useful if you want to keep inks away from each other,
for example, when printing on metallic surfaces. For details, see: An example of white framing.
Trap To:
•Objects
If checked, images are trapped to other objects. The image pixels are not replicated, instead the traps are created by "overprinting" single color separations.
•Images
If selected, images are trapped to other images. Trapping within images is not supported.
direction
This parameter controls how traps are placed when images are trapped:
The following settings are available:
|
|
"Into Image" |
Traps are placed in the image. |
|
|
"Center" |
Traps are centered along the edge between the image and the adjacent object. |
|
|
"Into Object" |
Traps are placed in the adjacent object. |
|
|
"Automatic" |
The trap direction is determined automatically on the basis of the color of the adjacent object and of the average color of that image area. |
Trap complex Bitmaps if possible
Sometimes trapping for complex bitmaps (many small elements) may not be what you want. It can be disabled here.
Convert Bitmaps to Graphics, if possible
To date, bitmaps were always converted to graphics, where possible. You can disable the function for trapping.
Creation
PostScript Level 2, if possible:
•enabled:
The traps are created without using the DeviceN color space. DeviceN color spaces are not reproduced correctly on PostScript Level 2 RIPs.
•disabled:
The DeviceN color space is used when required during trapping.