Rendering intent

[Johannes]

Hi!

At the LFP company I work at we have the rendering intent in the RIP set to different settings for CMYK Images(perceptual bpc) and CMYK Vector (relative colorimetric bpc).

Usually everything runs fine but at a few occasions I got a specific problem with PDF’s. You can’t see it until the file is in the rip and it’s been renderd. Squares appears around text and objects. And change the background color around the objects.

I know that it’s because of the different settings in the rendering and the original PDF sent to us are somehow created or saved in the wrong way. But is there any way to discover this problem before you got the file in the rip? What should we tell the customer to do not to have it happening again?

 

[aaronchan]

I've seen this problem before and seems like is about the file rather than the rendering intent that you use.
When your customer created the artwork, let's say from AI, he might start out with CMYK, then he, by somehow, imported an RGB image to it. On the screen, they both appear the same color, but actually, they are not. That's why you see 2 different colors after you print them out.

Aaron

 

[Magnus59]

If your source files are CMYK, this shouldn't make a difference unless you are doing CMYK-CMYK conversion. If your files are strarting as another colourspace, then yes, different rendering intents will result in different CMYK values from the same RGB or LAB value.

 

[Johannes]

Is it possible to detect those problem files in pit stop? What should I look for?

Would it help to flatten the PDF in Photoshop?

 

[Puch]

Look / Preflight for RGB graphic element in the incoming file. If there are such elements, you should convert to CMYK and flatten the artwork before sending it to the RIP. This way you will see all the problems in an early stage of the process.

 

[Johannes]

Thanks, I’ll try that

 

[Correct Color]

Johannes,

You are entirely correct in your initial asessment.

What happens is that the RIP will take certain objects in a vector file -- such as images or type with a drop shadow around them -- and render them first into bitmaps before proceeding to RIP the entire file.

So now that they are bitmaps, it applies the bitmap rendering intent to them, rather than the vector intent, which is applied to all the area around it. And that's the artifact you see.

Many, many years ago, that was the way most RIP's were set, but interestingly, when Adobe PDF RIP came out, and Caldera began using it as their RIP engine, they made a huge hullabaloo that it --Adobe PDF print engine -- solved this problem.

But yet if you went in and looked at their settings, they were set to perceptual/perceptual. And if you set any RIP -- with any engine -- that way, it will solve the issue. And it doesn't have to be perceptual; they just have to be the same. Also if you set any Adobe PDF print engine RIP to non-matching intents, you'll see the issue just as with any other RIP.

It is true that if you flatten or rasterize an image before you RIP it, you can usually get rid of this. But of course you lose your spot colors if you do. And it's usually best to make as few conversions or alterations as possible.

And, of course, the last thing you ever want to do -- particularly in large format -- is ever convert your RGB files to CMYK before print time.

Just try changing those settings in your RIP.

It'll work.



Mike Adams
Correct Color

 

[Johannes]

Johannes,

You are entirely correct in your initial asessment.

What happens is that the RIP will take certain objects in a vector file -- such as images or type with a drop shadow around them -- and render them first into bitmaps before proceeding to RIP the entire file.

So now that they are bitmaps, it applies the bitmap rendering intent to them, rather than the vector intent, which is applied to all the area around it. And that's the artifact you see.

Many, many years ago, that was the way most RIP's were set, but interestingly, when Adobe PDF RIP came out, and Caldera began using it as their RIP engine, they made a huge hullabaloo that it --Adobe PDF print engine -- solved this problem.

But yet if you went in and looked at their settings, they were set to perceptual/perceptual. And if you set any RIP -- with any engine -- that way, it will solve the issue. And it doesn't have to be perceptual; they just have to be the same. Also if you set any Adobe PDF print engine RIP to non-matching intents, you'll see the issue just as with any other RIP.

It is true that if you flatten or rasterize an image before you RIP it, you can usually get rid of this. But of course you lose your spot colors if you do. And it's usually best to make as few conversions or alterations as possible.

And, of course, the last thing you ever want to do -- particularly in large format -- is ever convert your RGB files to CMYK before print time.

Just try changing those settings in your RIP.

It'll work.



Mike Adams
Correct Color

Great answer. Thanks!

So as I thought, the easy fix is to use same rendering intent for vector and bit-map. Of course there are some compromises you have to do then depending on what rendering you choose.

So this is how I think and what my experience say:

To get the best color match between different machines with rather different wide gamuts, go for relative colorimetric + bpc. You also get more correct vector colors with this setting.

What you may be giving up by not using perceptual rendering intent is details in dark images and shadows.

Is this correct? Am I missing something?

 

[Correct Color]

To get the best color match between different machines with rather different wide gamuts, go for relative colorimetric + bpc. You also get more correct vector colors with this setting.

What you may be giving up by not using perceptual rendering intent is details in dark images and shadows.

Is this correct? Am I missing something?

Well, in order to have accuracy between different machines, you have to have profiles for each machine that are accurate characterizations of each machine on each media that you're using. No process will fix that if you don't.

Also it's important to note that there are vast differences between rendering intents from one icc profile-making engine to another, so if your profiles are not all made with the same engine, you can get some -- let's say -- unexpected results.

Also it is worth noting that almost all large format RIP's these days use the perceptual/perceptual setting as their default. I think mainly because you can get into trouble with RelCol, even with BPC on, on some smaller gamut media, even on a large gamut machine.

But with those caveats, yeah. I'd say you've about got it.


Mike

 

[Johannes]

Well, in order to have accuracy between different machines, you have to have profiles for each machine that are accurate characterizations of each machine on each media that you're using. No process will fix that if you don't.

Also it's important to note that there are vast differences between rendering intents from one icc profile-making engine to another, so if your profiles are not all made with the same engine, you can get some -- let's say -- unexpected results.

Also it is worth noting that almost all large format RIP's these days use the perceptual/perceptual setting as their default. I think mainly because you can get into trouble with RelCol, even with BPC on, on some smaller gamut media, even on a large gamut machine.

But with those caveats, yeah. I'd say you've about got it.


Mike

Ok!
I’ve made one profile for each material and machine so that’s covered.

You wrote that you should leave the files in RGB when printing wide format. I never heard that. Usually we get the files in FOGRA39 from our customers. Why is RGB better?

 

[Correct Color]

Johannes,

If you get the files in any CMYK working space, there's nothing you can do about it. You may as well use them. But the answer is that most large format printers printing on most large format media, and properly profiled, will have a significantly larger color gamut than all the standard CMYK working spaces. If you send color information to your printer in one of those spaces, you're typically leaving a lot of printer capability on the table.


Mike

 

[Johannes]

Johannes,

If you get the files in any CMYK working space, there's nothing you can do about it. You may as well use them. But the answer is that most large format printers printing on most large format media, and properly profiled, will have a significantly larger color gamut than all the standard CMYK working spaces. If you send color information to your printer in one of those spaces, you're typically leaving a lot of printer capability on the table.


Mike

I’ve been working with machines from Durst, Inca, Canon, HP Latex, VUtek the last 10 years and I can say that they almost print the whole ISOCoated/Fogra39 gamut or less. Often they are weaker in some area of the gamut. For instance intense red colors on the UV printers can be off. Same on HP lx570. I don’t think you will get much more out of the inks in those machines.

So if you get the files in RGB would that really make a difference? If you make the profiles to match ISOCoated and the machines barely print that colourspace, Would it not be better to receive the files in CMYK ISOCoated/Fogra. Then you know that the customer, if they got a calibrated screen or proof, know what to expect from the print.

 

[tngcas]

If you open the file and flatten it in photoshop (or another program) it'll fix the file. It's transparency issue.

 

[ederoos]

I’ve been working with machines from Durst, Inca, Canon, HP Latex, VUtek the last 10 years and I can say that they almost print the whole ISOCoated/Fogra39 gamut or less. Often they are weaker in some area of the gamut. For instance intense red colors on the UV printers can be off. Same on HP lx570. I don’t think you will get much more out of the inks in those machines.

So if you get the files in RGB would that really make a difference? If you make the profiles to match ISOCoated and the machines barely print that colourspace, Would it not be better to receive the files in CMYK ISOCoated/Fogra. Then you know that the customer, if they got a calibrated screen or proof, know what to expect from the print.

How are you making the determination about your device gamuts? Assuming you're using something to evaluate/compare like ColorThink Pro?

Fogra39, like GRACoL, is for offset litho which is known to have a smaller gamut than digital LF. The only reason I think where this might make sense is when you have to dumb the color down on your larger gamut devices to get everything to a completely common colorspace where gray balance alone is not acceptable. I agree with Mike that you might be leaving a lot of printer capability (value) on the table.

 

[Johannes]

How are you making the determination about your device gamuts? Assuming you're using something to evaluate/compare like ColorThink Pro?

Fogra39, like GRACoL, is for offset litho which is known to have a smaller gamut than digital LF. The only reason I think where this might make sense is when you have to dumb the color down on your larger gamut devices to get everything to a completely common colorspace where gray balance alone is not acceptable. I agree with Mike that you might be leaving a lot of printer capability (value) on the table.

In Caldera EasyMedia you can compare profiles. I think there is a tool for that in ONYX Rip also but I haven’t looked into it yet.

I got a feeling we are talking about different sorts of production here. If you get a nice epson/canon 10 color photo printer, then I agree that you certainly can print a good, wide gamuts.

I’ve been working at a quite big company where volume and speed are as important as quality. The reference was to match the offset department in quality. Sometimes we got a sheet straight from the offset press to match and it was not always easy even with good ICC-profiles. The Epson proof printers in the prepress department had no problem to print ISOCoated... they got good quality paper and hade 10-ish different inks. The files always came as ISOCoated.

 

[Correct Color]

Johannes,

I’ve been working with machines from Durst, Inca, Canon, HP Latex, VUtek the last 10 years and I can say that they almost print the whole ISOCoated/Fogra39 gamut or less. Often they are weaker in some area of the gamut. For instance intense red colors on the UV printers can be off. Same on HP lx570. I don’t think you will get much more out of the inks in those machines.

Well that's a pretty comprehensive list.

And a few things. First, I'm not much of a Durst fan. Maybe they've changed things since I last saw one, but when I did last see one, it was indeed a very small gamut machine for the huge money the client paid for it. Main reason was that its max dot size was ten picoliter and its max resolution was 900x900 as I recall. Meaning it ran out of ability to lay down ink way too soon, and there was nothing to be done about it.

The other manufacturers there though, all make machines that can beat the gamut of any litho CMYK space by a pretty good margin. The HP Latex machines, for example. Doesn't matter which model, they all use roughly the same printheads, roughly the same inks, and have roughly similar gamut capabilities. They're not huge gamut machines, but if you send Fogra or Gracol or the like to them, and your profiles capture all their capabilities, then yes, you're not using their full capabilities.

Obviously, Canon builds or brands or sells just about every type of printer. But almost all of them, from the iPF aqueous machines to the biggest -- as I still think of them -- Oce flatbeds are capable of significantly larger gamuts than Fogra or Gracol as well.

Inca and Vutek tend to be mid-range in terms of gamut size. But again, just about any machine from either of them will be able at least somewhat to surpass the gamuts of either of these color spaces.

I’ve been working at a quite big company where volume and speed are as important as quality. The reference was to match the offset department in quality.

Well that's probably the issue. For instance, on most media, the smaller series (570 and the like) Latex machines lose the ability to get what I consider a sellable red at the 8 pass setting. Going up to ten pass can make a pretty big difference. So how you set up your machine states on all these printers could very well be affecting the gamuts of your profiles.

Every situation is different, and it sounds like in your case there probably wouldn't be an advantage worth the effort to change your workflow, but as a general practice in large format printing, it's better not to convert to any working-space CMYK profile prior to print time, because they are all typically smaller gamuts than what your printer profile should be.

In Caldera EasyMedia you can compare profiles. I think there is a tool for that in ONYX Rip also but I haven’t looked into it yet.

No, there isn't a gamut viewer in Onyx. The one in Easy Media is actually a really dumbed-down version of my old all-time favorite gamut viewer, Monaco Gamutworks.


Mike