In 4/C procedure (CMYK) or whatever multi-color printing for that matter, dissimilar inks are pose downward inwards sequence inwards gild to create the concluding image. The sequence that the inks are pose downward tin terminate significantly alter the concluding printed result. Ink sequence tin terminate equally good impact whether the chore runs successfully or fails on press.Printing e'er involves a bird of compromise as well as the selection of ink sequence is no exception. However, spell in that location are few "rules" as well as surprisingly, virtually no documented information on this topic, in that location are several notable factors to reckon when determining the appropriate ink sequence to purpose for whatever specific application, namely:
1 - Conformance to an manufacture standard. For example, ISO 12647-2:2004 for procedure command inwards offset lithography standardizes the chromatic ink sequence to CMY – however, dark is acceptable equally either outset or in conclusion down.
2 - Ink tack - the stickiness of the ink that allows an over-printing ink to stick to an already printed layer of ink.
3 - Paper absorption - both smoothness as well as tightness of the surface affects ink tack.
4 - Time - moisture ink sticks/traps to dry out ink meliorate than moisture ink traps to moisture ink. E.g. unitized press (each unit of measurement lays downward i ink) or mutual impression cylinder press (one unit of measurement lays downward multiple inks) or unmarried color presses where the side past times side layer of ink is applied much afterward than the previous.
5 - Ink opacity - opaque inks enshroud underlying inks.
6 - Ink transparency - transparent inks combine amongst underlying inks.
7 - Ink coverage - the higher the coverage of an ink the less next inks are able to trap efficiently amongst it.
8 - The RGB to CMYK separation technique that was used.
9 - The printing method beingness used - i.e. sheetfed offset, flexography, gravure, etc.
In multi-color presswork the outset ink downward "traps" the i that follows. Tack - the stickiness of ink - is a major factor enabling inks to adhere to, or trap, i another.
In the proper sequence, the outset ink downward must guide hold the highest tack. Subsequent colors guide hold lower effective tacks, amongst a descending 2-to 4-point spread betwixt them.
In this outset example, a layer of Magenta was printed on a unmarried color press. Then an overlapping layer of Cyan was printed inwards a minute overstep after the Magenta ink had dried (i.e. wet-on-dry or "dry trapped"). The ink cinema thickness of both colors was the same.
The termination is real adept ink cinema trapping amongst a bluish where the ii colors overlap non having a bias towards Cyan or Magenta.The minute illustration was produced on a multi-color press. Again Magenta is printed outset downward onto dry out paper (i.e. wet-on-dry). Then a layer of Cyan was printed onto the soundless moisture Magenta ink (wet-on-wet or "wet trapped").
While the Magenta ink cinema was trapped good past times the dry out paper, the ink trapping for Cyan was non equally adept due to the fact that the Magenta ink was wet, as well as so the resulting bluish where they overlap has a decided reddish cast.In the tertiary example, the wet-on-wet printing method was used again, but amongst the ink gild reversed:
The termination is that the blue, where Cyan as well as Magenta overlap, forthwith has a decided Cyan cast. Note that this detail ink sequence is the criterion for CM inks inwards CMYK procedure color printing.Ramifications
Modern offset presses impress all iv (or more) inks inwards rapid succession, 'wet-on-wet'. The outset inks downward commonly adhere to the paper meliorate than afterward inks. In roughly cases the afterward inks tin terminate genuinely take away roughly of the before inks, depending on the relative tack of each ink inwards the sequence. Either way, the amount of i or to a greater extent than inks remaining on paper is commonly less than would hold upwards achieved on a "dry trapping" press, or amongst a drying arrangement betwixt each unit of measurement equally is accomplished past times roughly score of inter-unit drying system, such equally IR (Infra-Red) estrus for conventional inks, or UV (Ultra-Violet) lite for UV-curable inks.
Wet-trapping tin terminate equally good innovate an unstable functioning inwards darker tones as well as is oft cited equally i of the original problems inwards matching multiple presses to a criterion characterization information set, fifty-fifty when each press uses the same paper as well as ink.
So:
1 - Dry-trap printing processes tin terminate hit a greater color gamut than wet-trap printing.
2 -The sequence of the primary CMY inks helps determine the color integrity of the secondary colors (RGB)
3 -Changing the sequence of CMY inks tin terminate hold upwards used to enhance/favor specific secondary colors.
4 - Poor ink trapping inwards 4/C printing volition hold upwards revealed inwards a loss of gamut, color bias, lack of vibrancy/chroma, as well as a mottling/splotchy appearance inwards the secondary colors (RGB)
5 - With graded tack inks, the tack must hold upwards adjusted to reverberate the ink's novel position. E.g. If outset downward Cyan tack is xiv followed amongst an overprint of Magenta amongst a tack of eleven then, to hold adept trap, if Magenta becomes outset downward its tack must hold upwards adjusted to xiv as well as Cyan's tack adjusted 11.
6 - The farther apart ii ink units are on press, the meliorate their effective trap should be. I.e. In a KCMY ink sequence, C as well as Y (forming Green) volition trap meliorate than C as well as G (forming Blue) or G as well as Y (forming Red).
Addendum
Below are the typical trap values (Status T, Preucil formula) for dissimilar types of presswork equally good equally the CIEL*a*b* values according to ISO 12647-2:
As noted, the ISO criterion specifies that the chromatic inks are pose downward inwards CMY sequence amongst K beingness either the outset or in conclusion ink down. Traditionally, for almost offset applications, the ink sequence has been KCMY.
The preference for this ink sequence is probable the legacy of the ikon separation methods used inwards the past. Prior to today's desktop ikon editing applications, the conversion of RGB scans into CMYK images, was performed past times software inwards the scanner itself. The conversion method utilized UCR (Under Color Removal) techniques to optimize the ikon for the press equally inwards this example:
Note that inwards a UCR separation, in that location is real petty Black ink coverage compared to the C, G or Y plates. Note equally good that in that location is a large amount of Y coverage inwards the image, inwards part, because the Y element inwards the separation is beingness used instead of Black ink to grey, or darken, the image. This agency that laying Black ink downward outset provides a greater expanse of dry, non-inked, paper for the Cyan ink to trap to. In a KCMY ink sequence, running the transparent, high expanse coverage, Yellow ink in conclusion downward equally good has the do goodness of acting somewhat similar a gloss varnish to add together depth to the reproduction.In contrast, for newspaper production, Yellow is commonly the outset ink downward amongst Black ink the in conclusion down:
The argue that this ink sequence is preferred over a KCMY sequence is both related to the purpose of UCR separation techniques equally good equally the inks beingness used. For paper work:
laying Yellow downward outset helps to seal the paper thus providing a meliorate surface for the Cyan ink to trap to. Black ink in conclusion downward benefits from the 3 previous inks sealing the paper which helps the Black ink deliver maximum blackness as well as contrast. Maximizing the coverage of the chromatic C, M, as well as Y inks as well as minimizing the purpose of Black ink inwards images equally good helped images to hold equally much of their vibrancy equally possible given the pathetic character of paper beingness used. Finally, the Black ink used for paper operate tends to hold upwards of real pathetic character compared to the C, M, as well as Y inks. If it was outset down, it could move downward to the side past times side printing units as well as contaminate them."A wrench inwards the monkey works" - GCR separations
In today's ikon processing workflow, the default separation method uses GCR (Grey Component Replacement) rather than UCR techniques. In addition, many newspapers as well as publication printers are reseparating incoming ikon files inwards gild to apply GCR techniques inwards gild to cut back ink usage as well as growth color stability on press (more information is available HERE). Influenza A virus subtype H5N1 GCR separation, similar this example:
maximizes the purpose of Black ink inwards gild to cut back the amount of the to a greater extent than expensive chromatic C, M, as well as Y inks spell delivering virtually the same concluding color appearance inwards print. For paper work, the purpose of GCR separated images inwards a YCMK ink sequence may lower the effectiveness of the Yellow ink to seal the paper as well as so cut back the potential color gamut.Ramification
When evaluating the optimal ink sequence for a specific application, specially the seat of the Black printer, it is of import to reckon the type of separation techniques that were used to ready images for press as well as how those separation methods impact both ink trapping as well as printability.
Addendum - Ink Sequence for a two-color press
The recommended ink lay downward sequence for a two-color press is: outset overstep CM, minute pass: KY:
This sequence makes CM inks moisture trap which helps align the color termination amongst that of a four-color press. Also, because the primary chromatic colors are pose downward together, it facilitates color assessment. Black, beingness achromatic does non touching color. Yellow, beingness the greying element of C + Y does non number color equally much equally C as well as M.Adding a 5th, 6th, or to a greater extent than inks to the sequence equally good adds a score of complication.
Note that almost presses amongst to a greater extent than than iv colors are run amongst the outset units empty as well as available, amongst the KCMY inks inwards the in conclusion iv units. However in that location is no criterion practice, so which units are available volition vary from store to shop.
The full general guidelines are:
1 - If possible, boot the bucket on the procedure colors together inwards their criterion gild (KCMY). This is to avoid color shifts that powerfulness plow over off if their inter-press unit of measurement distance changes. This equally good helps avoid wash-ups.
2 - If possible do non motility the seat of the KCMY inks. This is to avoid having to do a consummate wash-up of press units.
3 - If the extra color(s) volition non hold upwards over-printed past times procedure colors it would preferably hold upwards in conclusion down.
4 - If the extra color(s) are opaque as well as volition hold upwards over-printed past times procedure colors it would preferably hold upwards outset down.
5 - If the extra color(s) are transparent as well as volition over-print, or hold upwards over-printed, past times procedure colors, its seat should hold upwards furthest away from the color it volition trap with. This is to assist larn inwards a dry-trap province of affairs increasing print-ability as well as reducing mottle.
6 - Metallic inks, whenever possible, should hold upwards in conclusion downward unless they are specifically formulated to hold upwards outset downward inwards gild to hold upwards over-printed (e.g. MetalFX printing). Note that metallic element inks are commonly varnish coated as well as that many printers boot the bucket on the in conclusion press unit of measurement available for the varnish. This may as well as so involve that the metallic element ink hold upwards outset downward fifty-fifty though it won't hold upwards over-printed.
Some examples:
Spot color volition hold upwards over-printed past times procedure colors:
Opaque spot color volition over-print procedure colors:
Metallic silver:
Hi-Fi color printing where transparent extra procedure color inks volition hold upwards trapped amongst criterion procedure inks:
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