GRACol and uncoated

[longlimb]

So would it be safe to say I would want to shoot for the same dot gains for uncoated as I did for coated? I arrived at a very decent gray for coated, so would I want the same dot gain for uncoated but with the lower SID's?

 

[gordo]

So would it be safe to say I would want to shoot for the same dot gains for uncoated as I did for coated? I arrived at a very decent gray for coated, so would I want the same dot gain for uncoated but with the lower SID's?

You want the same final tones in your presswork, it will take different dot gains to get there.


best, gordon p

 

[longlimb]

Would you say an uncoated TVI is typically lower or higher than coated ones? I'm getting ready to do an uncoated press calibration in the morning and I have the GRACoL target dot gains for coated "in a perfect world" but I don't see anything for uncoated.

Basically, if I use the same target curve that I used for coated to do my uncoated plate curve, will the uncoated sheet be close granted some adjusting might need to be made?

 

[roger]

uncoated vs. coated sheets:
thicker ink film on the rollers,
lower solid ink density on the sheet,
higher dot gains (TVI) on the sheet

you will be targeting higher dot gains with uncoated. If you target the same dot gains as you got for coated, the imagery and spot color builds will be too light/thin.

Roger

 

[longlimb]

So with my coated plate curve I have, I am getting around an 18% dot gain at the 50%. I wouldn't want that same amount with uncoated?

My uncalibrated press run will obviously have way higher gains. But wouldn't I still want to shoot for that 18% gain at the 50% like I did on the coated?

Example:

Uncal Coated 50% screen reads 72 - so I cut back the 50% area on my curve by 4 so I would hit my 68 (18% gain)
Uncal Uncoated 50% screen reads 77 - so I would cut back the 50% area on my curve by 9 so I would hit 68 (18% gain)

Is this what I would do, right? Roughly of course...

 

[meddington]

So with my coated plate curve I have, I am getting around an 18% dot gain at the 50%. I wouldn't want that same amount with uncoated?

Keep in mind that TVI is a a value calculated from the solid density and the density of the particular percentage your measuring. Since with uncoated, your solid densities will be lower, your TVI will have to be higher in order to have the same tone at 50% as a coated print. One of the reasons that targeting TVI is a bit ambiguous.

Uncal Coated 50% screen reads 72 - so I cut back the 50% area on my curve by 4 so I would hit my 68 (18% gain)
Uncal Uncoated 50% screen reads 77 - so I would cut back the 50% area on my curve by 9 so I would hit 68 (18% gain)

Again, because the solids density is lower, doing the above would give you a lighter tone. A better method would have you matching tone response based on density rather than TVI, and determining which input dot value yeilds the density tone and adjusting from there. The G7 method is an option, or visit Gordo's blog.

You could also aim for ISO 12647-2 TVI curves for your particular paper type.

 

[longlimb]

Ahh. I think I understand. Thanks meddington. So how do I know what is a good dot gain to shoot for with uncoated and GRACoL? Is there not one for uncoated? Is the ISO 12647-2 curve a better way to go when talking about uncoated?

 

[gordo]

Ahh. I think I understand. Thanks meddington. So how do I know what is a good dot gain to shoot for with uncoated and GRACoL? Is there not one for uncoated? Is the ISO 12647-2 curve a better way to go when talking about uncoated?

Dot gain is NOT the issue. For the purposes of your question, there is no "good" or "bad" dot gain to shoot for.
You are shooting to align the final presswork tone values. I.e. for a 50% tone request in the original file you should achieve the same 72% on both coated and uncoated sheets. It basically does not matter what the dot gains are - as long as you achieve the desired tone on press.
These two blog entries explain the process - in the context of printing at higher SIDs - the principle is the same though.
http://qualityinprint.blogspot.com/2009/01/printing-at-dmaxx-part-3.html
http://qualityinprint.blogspot.com/2009/01/printing-at-dmaxx-part-4.html

best, gordon p

 

[longlimb]

You just answered my question. Sorry I don't think I asked it very well. I know my curve will be different. But if 72% at the 50% screen is what I ended up with on coated, then 72% is what I would want on uncoated as well... even with lower SID's.

Thanks guys!

 

[gordo]

You just answered my question. Sorry I don't think I asked it very well. I know my curve will be different. But if 72% at the 50% screen is what I ended up with on coated, then 72% is what I would want on uncoated as well... even with lower SID's.

Right, and don't forget - you can always raise your SIDs on uncoated to determine the optimum SIDs you can run with (along with good plate curves) to get the best result possible from your process.

best, gordon p

 

[chromix]

guys, guys, guys.....

Unless I'm missing the point, I think you've missed the point.

GRACoL is based on G7, NOT TVI.

You should balance your press using G7 regardless of the coating of the paper.

That will ensure you get the closest match in the highlights and also take advantage (or compensate for) the maximum density available.

G7, *not* TVI

regards,

Steve Upton

 

[longlimb]

I agree. That was what I was doing. But when I calibrated on gloss to GRACoL I saw where my TVI ended up. I was curious if that same TVI would apply to uncoated. But it won't. I redid my plate curve for uncoated earlier this week and it looked awesome.

 

[chromix]

Ah! good. understood.

well then, I was missing something.

I'm glad it worked well.

regards,

Steve

 

[RGPW17100]

We were told that we could not certify the Uncoated targets. Because of the limited color gamut you can produce on oncoated it would not be possible to certify the sheet. Our matte and gloss profiles were almost exactly the same and we were able to certify them.

 

[longlimb]

If you couldn't get G7 certified on uncoated, what did you decide to use as a standard for uncoated? SWOP?

 

[RGPW17100]

We still offer cougar uncoated. We were able to match the G7 for it but Idealliance would not certify it. We are still G7 certified. We are a smaller print shop and have not had customers request G7 certified stamping or branding of any kind. We use the G7 status more as a selling point rather then using it as a standard. With the way the economy is now G7 and FSC and all the other gimmicks for people to make money are on the back burner. In the last 100 quotes or more we have not had a single request for carbon profiling, G7, green printers or anything. Everybody wants cheap now and they dont really care what it is.

 

[cmcfarling]

I'm reviving this thread from 6 months ago because I was reading through it and was confused by some posts that seem to contradict each other.

longlimb:

Uncal Coated 50% screen reads 72 - so I cut back the 50% area on my curve by 4 so I would hit my 68 (18% gain)
Uncal Uncoated 50% screen reads 77 - so I would cut back the 50% area on my curve by 9 so I would hit 68 (18% gain)

meddington replied with:

Keep in mind that TVI is a a value calculated from the solid density and the density of the particular percentage your measuring. Since with uncoated, your solid densities will be lower, your TVI will have to be higher in order to have the same tone at 50% as a coated print. One of the reasons that targeting TVI is a bit ambiguous.

Again, because the solids density is lower, doing the above would give you a lighter tone. A better method would have you matching tone response based on density rather than TVI, and determining which input dot value yeilds the density tone and adjusting from there.

Then later on gordo mentions:

Dot gain is NOT the issue. For the purposes of your question, there is no "good" or "bad" dot gain to shoot for.
You are shooting to align the final presswork tone values. I.e. for a 50% tone request in the original file you should achieve the same 72% on both coated and uncoated sheets. It basically does not matter what the dot gains are - as long as you achieve the desired tone on press.

It seems that meddington and gordo are giving conflicting info. Maybe I'm just missing something though so please clarify if so. Part of my confusion stems from how dot gain is being defined here. In other words what is the reference dot that is being used as the comparison for the printed dot. Is the reference dot the digital file dot size or is it the dot size that's imaged on the printing plate.

When the reference dot is the digital file then 18% TVI has the same meaning regardless of if you're referring to coated or uncoated stock, right? Your file specifies a 50% dot and you want a 68% dot on the paper. Since you want a 68% dot on paper, whether coated or uncoated, that would be considered 18% TVI.

Now if the reference dot is the dot as it is imaged on the plate, then I see where you'd have two different TVI values. For the uncoated stock you would have to image the dots a little bit smaller since they'll grow a little bit more. Isn't that what longlimb was saying when he asked about cutting the curve back more for the uncoated stock? It seems to me that that's what you'd have to do but meddington said that was not what to do.

I'm not calling anyone out for being write or wrong here, I'm just curious myself and was looking for clarification.

 

[Bret Hesler]

I think they are basically saying the same thing. The confusion might be in the wording choice that Gordo made:

"...I.e. for a 50% tone request in the original file you should achieve the same 72% on both coated and uncoated sheets. It basically does not matter what the dot gains are - as long as you achieve the desired tone on press..."


I think he meant to say "the same 72% (tone) on both coated and uncoated sheets" and the second sentence is where they (and I) agree.

Starting with a paper with a density of 0.06, and Gracol aims for black density (1.70) and midtone (0.06+.50=0.56) you get a dot gain of 20%.

The same midtone density (tone) with a black density of 1.20 on uncoated paper makes a dot gain of 23.7%

20% dot gain on an uncoated sheet with a black density of 1.20 results from a midtone density of 0.515 (which would be 16.4% dot gain at 1.70 density)

In summary, you need higher dot gain on uncoated paper with lower density to achieve the same tone.

Bret

 

[gordo]

To cmcfarling:

I am not referring to G7/GRAcoL 7.

Dot gain specifications came from a film workflow, where the standard was a 50% dot in the film when a 50% dot was requested in the file. Nobody measured the plate. They measured the press sheet.
So, the reference dot used as the comparison for the printed dot is the tone value requested in the file - not whatever is on the plate.
I.e. In PShop/Illustrator the image is specified as having 50% a tone.
In the traditional (film-based) world the target is "18% dot gain"
That would then result in a measured 78% tone on press where the file specified a 50% tone.

Looked at another way - different types of halftone screening and plate imaging will result in different dot gains (e.g. a positive film workflow will have a different dot gain than a negative film workflow. Finer screens e.g. FM screens will have a higher dot gain than coarser AM screens.

So, an 18% dot gain is not really a useful target to achieve a common visual appearance. What is relevant is the final tone value on the press that the 18% dot gain would deliver. I.e. 18% dot gain is not the target. A 78% tone value on the press sheet for a 50% tone request is the actual target.

So, the process is to use whatever tone on plate you need to use to achieve whatever dot gain on press is required to achieve the target 78% on the press sheet when the file requests a 50% dot.

hope that's a bit clearer

best, gordo

 

[cmcfarling]

gordo, where did you get 78%? Is that a typo or am I missing 10% somewhere?

So when longlimb said

Uncal Coated 50% screen reads 72 - so I cut back the 50% area on my curve by 4 so I would hit my 68 (18% gain)
Uncal Uncoated 50% screen reads 77 - so I would cut back the 50% area on my curve by 9 so I would hit 68 (18% gain)

was he not correct?

If dot gain/TVI is defined as the difference between the printed dot size and the requested dot size as it is defined in the digital file, and the printed dot comes out the same size on coated or uncoated (or even newsprint) paper, then the dot gain in both cases would be the same.

Ex.
50% dot size in digital file
68% dot size desired on coated paper = 18% TVI
68% dot size desired on uncoated paper = 18% TVI
68% dot size desired on newsprint = 18% TVI
68% dot size desired on toilet paper = 18% TVI

Now I realize that that's not actually how it works. My point is that by definition, the above is true, yes? I realize that a 50% dot printed on uncoated paper will grow/expand more than when printed on coated paper. So therefore the uncoated paper will have a higher TVI than the coated paper. The typical way to account for that (assuming CtP workflow) would be to reduce the size of the 50% dot when it is imaged on the plate. So in this sense of TVI we might have something like this:

50% dot size in digital file
68% dot size desired on coated paper = 50% dot size on plate = 18% TVI
68% dot size desired on uncoated paper = 46% dot size on plate = 22% TVI

So now there are two ways to express TVI. The first example is calculated as printed_dot_size - digital_file_dot_size and the second is calculated as printed_dot_size - plate_dot_size. Shouldn't the definition be changed to correspond to the second example since that is what really matters?

I understand the correlation between the various densities when calculating the TVI and how the Murray-Davies Equation is used to do so (generally). Using a densitometer you'd measure the paper then a solid ink patch and then a tint patch. The densitometer calculates the dot area (a.k.a dot size, tone value) using the Murray-Davies Equation. The posts on this thread that were focusing on the calculations used to derive the tone value were going beyond the scope of the question I think. When it comes down to it, what is important is the tone value (the actual number) itself, which i think is what gordo was trying to convey in a previous post.

I may be rambling a bit here but my main points are this...
1)The simple definition of TVI does not really explain what TVI is.
2)I believe longlimb was correct when he asked about cutting his plate curve back for the uncoated paper.

Am I wrong on either of those points or anything else above?