Understanding Ink Limits

[bellevuefineart]

Onyx Production House 7.3
Epson 9800

I'm having a hard time understanding ink restrictions. I've gotten to the end of profiling a paper, and the last swatch to print is for ink restrictions. In the advanced tab, you select a number between one and four based on the swatch that was printed.

So you have these lines, C+K+R and R+K etc. The swatches gradiate until they finally all become black. How do I choose which one should be the correct value? I'm not sure what I'm supposed to be looking for.

[Hotspur]

Hi

I think you mean Ink Limits...

It's a difficult thing to explain unless you are looking at the swatch.

Run your eyes from light to dark (left to right). If the colours are all dry and even and simply get darker right up to the end it is said that you have no "artifacts" to deal with.

In this case you can simply set your limits when the colours have gone to a solid black. This normally happens for the single colours around 2.2 and the combinations at around 3 to 3.3.

Setting them any more than this is simply a waste of ink.

However often you will see a change in the patches as you scan the swatch from left to right. These changes are called artifacts and can be varied.

For example, they might not dry beyond a certain point and thus you would call your limits at the last dry patch - if you don't your final profile might produce wet prints with the current settings.

You can of course go back and raise the heater temps, slow the print speed etc - this might push the drying point up and allow you more darker colours within your limit, increasing gamut.

Artifacting includes other things as well - you might get shadows along the edge of the patches "picture framing" caused by too much ink drying unevenly from the outside into the centre of the patch.

You can see matting (especially in black) where the level of ink is too high to form a good gloss.

Sometimes you get "coalescence" which looks like a coarse, oily dot patten where the high ink level has not been given time to sink into the media / coating properly.

Basically any noticeable change in the look of the patches which you don't want to see in the final image - that is where you should be limiting.

Once you limit at a point, you are often restricting gamut to a certain extent (usually in the darker RGBs). Sometimes gamut is more important than the artifact you see and thus the limit is set higher than you would otherwise choose - it's your decision.

Problems occur when you are forced to set a limit at a low level due to bad artifacting - for example your patches simply wont dry (assuming you've upped the heaters, slowed the printer etc) unless you limit all of them to something under 2.5

You have two options. either declare this media as incompatible - sometimes the ink/media/printer comination just isn't a good match.

Or you can set the limits at this low level and accept your profile will never be a great one.

Two points to note here - you can use Black Ink Compensation to prevent the inevitable "capping" that will occur with such low limits.

Capping is where you get a strange grey tone amongst your shadows in a print - the colour gets deeper but just before going to black you have a grey band.

This "missing" shadow tone is the gap between the point where you have limited the ink and the point where the black is brought in.

This gap can be filled with black so that in the final print it appears to be normal. The B.I.C setting replaces these missing colour tones with black - the lower the ink limit, the higher the B.I.C needs to be from 1 to 5.

The other point, and one which took me some time to realise, is that actually the icc will do a good job of trying to fill in the missing shadow colour tones for you. Even though you may have to set low limits - say 2.4 for the RGB you think that you will now lose every colour after that point from your gamut and your profile will have no darker colours at all.

Just continue and build an icc - look at the patches you are reading - you will see many of the tones you thought you had lost in the limiting process. The icc is using other combinations of CMYK to achieve an acceptable result. It is often worth perservering and building an icc profile even if you have set low limits to get a troublesome media profiled (especially if someone is paying you to do it!)

However, hopefully you have a "good" media and can set the limits to somewhere near the norm - 2.2 for the CMY and 2.8-3.0 for the RGBK. At these settings you are usually good to go.

Ink Limits are one of those "black art" things where everyone has their own interpretations and views - these are just mine from experience & Onyx's training so others might have more advice that will help.

Good luck!

[bellevuefineart]

(10-23-2009 02:49 PM)Hotspur Wrote:  Hi

I think you mean Ink Limits...

It's a difficult thing to explain unless you are looking at the swatch.

Run your eyes from light to dark (left to right). If the colours are all dry and even and simply get darker right up to the end it is said that you have no "artifacts" to deal with.

In this case you can simply set your limits when the colours have gone to a solid black. This normally happens for the single colours around 2.2 and the combinations at around 3 to 3.3.

Setting them any more than this is simply a waste of ink.

However often you will see a change in the patches as you scan the swatch from left to right. These changes are called artifacts and can be varied.

For example, they might not dry beyond a certain point and thus you would call your limits at the last dry patch - if you don't your final profile might produce wet prints with the current settings.

You can of course go back and raise the heater temps, slow the print speed etc - this might push the drying point up and allow you more darker colours within your limit, increasing gamut.

Artifacting includes other things as well - you might get shadows along the edge of the patches "picture framing" caused by too much ink drying unevenly from the outside into the centre of the patch.

You can see matting (especially in black) where the level of ink is too high to form a good gloss.

Sometimes you get "coalescence" which looks like a coarse, oily dot patten where the high ink level has not been given time to sink into the media / coating properly.

Basically any noticeable change in the look of the patches which you don't want to see in the final image - that is where you should be limiting.

Once you limit at a point, you are often restricting gamut to a certain extent (usually in the darker RGBs). Sometimes gamut is more important than the artifact you see and thus the limit is set higher than you would otherwise choose - it's your decision.

Problems occur when you are forced to set a limit at a low level due to bad artifacting - for example your patches simply wont dry (assuming you've upped the heaters, slowed the printer etc) unless you limit all of them to something under 2.5

You have two options. either declare this media as incompatible - sometimes the ink/media/printer comination just isn't a good match.

Or you can set the limits at this low level and accept your profile will never be a great one.

Two points to note here - you can use Black Ink Compensation to prevent the inevitable "capping" that will occur with such low limits.

Capping is where you get a strange grey tone amongst your shadows in a print - the colour gets deeper but just before going to black you have a grey band.

This "missing" shadow tone is the gap between the point where you have limited the ink and the point where the black is brought in.

This gap can be filled with black so that in the final print it appears to be normal. The B.I.C setting replaces these missing colour tones with black - the lower the ink limit, the higher the B.I.C needs to be from 1 to 5.

The other point, and one which took me some time to realise, is that actually the icc will do a good job of trying to fill in the missing shadow colour tones for you. Even though you may have to set low limits - say 2.4 for the RGB you think that you will now lose every colour after that point from your gamut and your profile will have no darker colours at all.

Just continue and build an icc - look at the patches you are reading - you will see many of the tones you thought you had lost in the limiting process. The icc is using other combinations of CMYK to achieve an acceptable result. It is often worth perservering and building an icc profile even if you have set low limits to get a troublesome media profiled (especially if someone is paying you to do it!)

However, hopefully you have a "good" media and can set the limits to somewhere near the norm - 2.2 for the CMY and 2.8-3.0 for the RGBK. At these settings you are usually good to go.

Ink Limits are one of those "black art" things where everyone has their own interpretations and views - these are just mine from experience & Onyx's training so others might have more advice that will help.

Good luck!

My God Man! That's the best explanation I've found. In fact, this is FAR better than Onyx's own white papers and videos. They should pay you to publish this on their website.

[Scott]

I'm glad to see Hotspur hopped in the conversation...that was my hope.

I also have to agree with bellevuefineart, that was a most excellent explanation, and far more clear that anything I have ever read from Onyx.

It looks like I really might need to get a wiki going or something to capture information like this.

[bellevuefineart]

(10-23-2009 04:36 PM)Scott Wrote:  I'm glad to see Hotspur hopped in the conversation...that was my hope.

I also have to agree with bellevuefineart, that was a most excellent explanation, and far more clear that anything I have ever read from Onyx.

It looks like I really might need to get a wiki going or something to capture information like this.

Yeah, three cheers to Hotspur. That was the most right-on explanation I could imagine. A one hour call to Onyx would not have been as efficient. Just spot on. Can you imagine a white paper like that from Onyx, along with a few snap shots of the grid, with arrows and circles around the values chosen for a specific media. Oh my god. I feel like somebody turned on the lights all of a sudden.

[Scott]

(10-23-2009 06:00 PM)bellevuefineart Wrote:  Can you imagine a white paper like that from Onyx, along with a few snap shots of the grid, with arrows and circles around the values chosen for a specific media. Oh my god. I feel like somebody turned on the lights all of a sudden.

I know exactly what you mean. I understand the basic idea, but always wished I had someone right next to me that could say "well, looking at this swatch I would pick this value and here is the reason why..." Hotspur's post did exactly that, as opposed to the training I received at Onyx years ago where the trainer said "Okay, here's the ink limit swatch, so let's pick the best value. Let's go with 2.x. Moving to the next step..."

I never understood why he didn't go into depth about WHY he picked that one.

I never really got adequate training though, so I don't want to knock their training too bad as I've never been through a full course, I just got a free 4 hour crash course (right before 7.0 release) walking us through creating a profile. It was more the theory behind it rather than alot of specifics. Maybe you get all that, and time for Q&A when you actually pay for the training, haha.

[Hotspur]

Glad it might be of help - i'm surprised any of it made sense (late Fri night after a few glasses of wine!)

You can take this further - drying time for instance.

The longer you let the patch dry, the higher you can set your limits & the better your profile. So how long do you wait?

Say your media vendor has a 60" Z6100 to build his profiles. He will time how long it takes for the print to get rolled up in the take up system - it must be dry by this point (say 5 mins)

Thus he prints his ink limit swatch and puts a 5 min timer on it before assessing. He will find that after 5 mins the patch is much dryer than an immediate assessment and by setting them at this point he gets a much bigger gamut & all is well. He then posts his Z6100 profile on the web.

Now let's assume the end user downloads the profile and has a 42" Z6100 which comes with a catch basket....

He doesn't have 5 mins dry time to play with - the prints need to be instantly dry so he's got big issues - I've never seen a Z6100 profile published that distinguishes between the two - but it's all part of the decision-making process.

It's why everyone should build their own profiles - you optimise them for your own particular workflow and ink limits play a big part in this.

It's also interesting to see where the ink limits have been set on a vendors profile for other reasons.

If you accept that any limit set beyond the point where the patches are solid black is simply a waste of ink (assuming no drying issues) take a look at where the vendor has set the limit and then ask yourself who is selling you the ink...

When you build your own profiles it's not just the quality you are optimising.

[bellevuefineart]

Your my new hero. Excellent.

[IIDave]

I agree with everyone, Hotspur's explanation was extremely enlightening, but I have a couple of question in the same vein that maybe you all can answer:

-On the Onyx Ink Limit Swatch BIC Limit Test at the bottom of the page... what am I supposed to get from this? I read a couple of things about light inks and how you can see if the limit is too low here, but what is it supposed to look like?

-In the M+K+G (number 2) it takes a while before the Magenta cast is completely gone from the solid looking patches. Should I pick the spot where it becomes mostly black, or should I set the limit higher up where it is completely black?

-Finally -- what does it mean? CMY+K vs K+CMY vs CMYK.... wha?!?!

[MarcoRoos]

(10-27-2009 09:33 AM)IIDave Wrote:  I agree with everyone, Hotspur's explanation was extremely enlightening, but I have a couple of question in the same vein that maybe you all can answer:

-On the Onyx Ink Limit Swatch BIC Limit Test at the bottom of the page... what am I supposed to get from this? I read a couple of things about light inks and how you can see if the limit is too low here, but what is it supposed to look like?

-In the M+K+G (number 2) it takes a while before the Magenta cast is completely gone from the solid looking patches. Should I pick the spot where it becomes mostly black, or should I set the limit higher up where it is completely black?

-Finally -- what does it mean? CMY+K vs K+CMY vs CMYK.... wha?!?!

Hi IlDave

The explanation behind the CMY+K and WhateverWhatever+Whatever is:
all colors before the '+' sign are evenly increasing. For example: CMY+K means that with each step there is 5% of C and M and Y added. Once they reach their maximum which is at 100% it starts to add incremental steps of 5% of the color behind the '+' sign.

this also explains why the bleeding is mostly at heaviest in the CMYK and CMY+K steps.

The light ink swatches at the bottom show you the bleeding that might occur in areas you might not expect bleeding at all. For example: a dark skin tone doesn't look like there is a lot of ink used, but in reality you are probably using 70%Y, 80% light Magenta, 20 Magenta and probably some cyan. Which might be a lot more than is being used with dark greens where you don't use the light inks anymore.

Something I would like to add to the explanation above:
when using the advanced ink restrictions and relatively low ink limits there still might be a chance to create a good ICC profile by using proper ICC GCR settings in the ICC Options dialog (the final step in Media Manager).

The higher the black start you use to more visual the problem with low ink limits will be.
The lower the black start, the more black ink you add into the light areas so the more contrast you add. In most cases this solves the problem with the 'grayed out' shadows. The default ONYX settings for GCR should never be used! They are far too high on any printer I ever profiled (or anyone else at Color Concepts, and we create around 3000 profiles each year!).

Ink limits are very hard to explain and are by far the hardest part in the profiling process. It already starts with the ink-restrictions. Most people use ink restrictions that are far too high because they restrict on density. Restricting on density makes no sense (unless you're profiling a backlit media or doing direct to textile on a flag material or so) because density doesn't tell you anything about the color and/or the gamut you're going to get. Much better is to limit the individual ink channels on maximum Chroma. Chroma limitations guarantee an accurate restriction because you limit the printer at the point where it creates the maximum amount of color (gamut) on that particular media. It also needs some practice, but it will give you great ink limits at the end (assuming you're using a more or less decent media ;-)).

If you want I can write something about chroma and the relation between all the steps after using that. But I first need to find some time then ;-).

Ciao!
Marco

[virtu]

(10-27-2009 11:31 AM)MarcoRoos Wrote:  

(10-27-2009 09:33 AM)IIDave Wrote:  I agree with everyone, Hotspur's explanation was extremely enlightening, but I have a couple of question in the same vein that maybe you all can answer:

-On the Onyx Ink Limit Swatch BIC Limit Test at the bottom of the page... what am I supposed to get from this? I read a couple of things about light inks and how you can see if the limit is too low here, but what is it supposed to look like?

-In the M+K+G (number 2) it takes a while before the Magenta cast is completely gone from the solid looking patches. Should I pick the spot where it becomes mostly black, or should I set the limit higher up where it is completely black?

-Finally -- what does it mean? CMY+K vs K+CMY vs CMYK.... wha?!?!

. Much better is to limit the individual ink channels on maximum Chroma. Chroma limitations guarantee an accurate restriction because you limit the printer at the point where it creates the maximum amount of color (gamut) on that particular media.

[IIDave]

INK RESTRICTIONS!!!

Oh Boy! You know everything I have read here points at Ink LIMITS being the mystery... but I can't figure out the damn RESTRICTIONS!

Where am I supposed to set them!? The info in ONYX's PDF and help is so vague... Am I going for a solid color? Should I still see dots? And the Advanced tab... yarg!

HELP!

[MarcoRoos]

(11-03-2009 09:43 AM)IIDave Wrote:  INK RESTRICTIONS!!!

Oh Boy! You know everything I have read here points at Ink LIMITS being the mystery... but I can't figure out the damn RESTRICTIONS!

Where am I supposed to set them!? The info in ONYX's PDF and help is so vague... Am I going for a solid color? Should I still see dots? And the Advanced tab... yarg!

HELP!

Dave

Setting damn restrictions is VERY easy! ;-) I'm joking....

The best way to set them is by using Chroma values....Let me explain:
In ONYX Media Manager in the ink restrictions tab there is a button "Measure tool" this measure tool enables you to measure the ink restriction swatch with an i1 or Pulse. There are 3 choices: LAB, Density and LCH. LAB makes no sense, unless you are able to interpret LAB values. Density makes no sense either because it doesn't tell you anything about color. It only tells you something about the difference between the patch you are measuring and the white of the media.

LCH values are mathematical color values, like LAB but in a different graph. L stands for Luminance (or ligthness), the same as we use in the LAB model. The lower the value the darker the color is (zero is absolute black, means no light, means no reflection, means we don't see anything ;-)). L 100 means absolute white (like looking into a nuclear explosion, which will make you go to L0 immediately).

C means Chroma which stands for the distance from the L axis. The further the C value is from the L axis the further it goes to the 'outside' of the color space, which means: the higher the C value the more color you're getting.

H means: Hue, which means the angle the color is going. Some colors (cyan for example) tend to get more blueish when you print more ink, we call this a 'hue shift' and believe me: you don't want to see hue shifts!

The trick of setting ink restrictions is to find the maximum C value. What you will find is that the patches you are going to measure look darker but the C value is not increasing anymore. This means that you are adding ink to the media without gaining color! (in other words: you are getting more density but no more color).

By ticking the "Plot measurements" option at the bottom of the dialog you can even draw a graph of your measurements. When you start measuring at the 100% patch you will the measurements going up till they start bending to the left. At the point it starts to bend is where you want to restrict that particular color channel.

Do this for every color and you will have perfect ink restrictions. Except for the black ink of course, since black is at the L axis and the distance will always be very small (in Dutch we say: "there is no color" :-) ).

You will find the ink LIMIT also easier now, because in most cases people tend to print far too much ink, with less result.

I hope this helps!

Ciao!
Marco

P.S. This is the first and last time I do this for free ;-) (I am still Dutch!).

Good luck!!