Forgive my ignorance - is it this simple ... yet this complicated?

[ScotJ]

I'm coming from a digital large format background, and we moved into a QM DI about 6 months ago.

I self taught the basics of desired dot gains, required densities, and the perils of reaching these targets.

We are in the process of installing a 6 colour akiyama - and I'm curious if the colour configuration is that "simple." I know the targe densities vary from press to press, but beyond reaching desired dot gain curves and appropriate densities - is there much more to it?

We plan to bring in an experience colour management consultant to help with this, but I'd like to have a knowlege of the objoectives we're trying to reach none the less.

Any info would be appreciated!

[glenncolorguy]

The concepts involved in process control for offset are reasonably simple.....application is not.

Density and dot gain may rough you into the territory...if you have accurate proofs to begin with.....but there is much more to the process.

Density needs to be based on L*a*b* values, and will vary with different ink types. MY, CM, CY overprints are as important as primaries and must be taken into consideration. Graybalance-the most important component-is to some degree predicted by density+dot gain but not entirely, and this must also be under control. In addition, determining press conditions is far more difficult than often thought because press variability is a major factor. Was your test calibration run really representative of typical press output (Almost certainly not).

But far beyond all technical considerations are the human factors. How will you implement process control in the pressroom? How will you achieve needed cooperation between prep and press? How will you collect data to assure continuing compliance with objectives? What procedures do you have in place to adapr to changing conditions on press? What will your team do when running to the numbers seems not to work?

Feel free to contact me directly on any of these issues.

[gordo]

Density needs to be based on L*a*b* values, and will vary with different ink types.

Perhaps worthy of a separate discussion.
I can't quite agree with that statement.
Density is an indirect measure of ink film thickness.
L*a*b* values are a measure of color.
These are two separate but related factors that need to be dealt with.
The function of the press is to lay down a film of ink. It does not know or care what color that film of ink is.
So, IMHO, density needs to be correct in order to avoid issues like ink tailing/slinging, and over emulsification, etc. At the correct ink density (ink film thickness) the color (L*a*b* values) should be within the target for the process (e.g. ISO 12647-2)
Put another way, you need to hit the correct density at which point your L*a*b* values should fall into place. If not you may have to select a different primary ink hue set/series.

best, gordo

[David Milisock]

A new press will require that a media linierization, ink limit dot gain curve be created this will create plates that have a preset curve for your paper. Many companies only use one some use two, one for coated paper and one for uncoated paper.

These curves will generate a TIC total ink coverage for each media, simply use ICC profiles for your applications that are equal to or less than the TIC for the media press.

Once this is done DO NOT change inks, use the same inks used for the creation of the curve.

[Bloodsaler]

As I know,DI press is hard to calibrate by human,it`s almost auto.One client of my boyfriend have brought this press,but the sample often reddish,even the heidelberg engineer can`t solve this problem~

[David Milisock]

Heidelberg have people and then they have people, Kodak has the same issue.

[gordo]

A new press will require that a media linierization, ink limit dot gain curve be created this will create plates that have a preset curve for your paper. Many companies only use one some use two, one for coated paper and one for uncoated paper.

These curves will generate a TIC total ink coverage for each media, simply use ICC profiles for your applications that are equal to or less than the TIC for the media press.

Once this is done DO NOT change inks, use the same inks used for the creation of the curve.

I find this very confusing.

What do you mean by "media linierization"?

What do you mean by an "ink limit dot gain curve"?

TIC is a function of how an RGB to CMYK conversion is made. Not curves (plate or press).

thx, gordon p

[fiatlux]

Heidelberg have people and then they have people, Kodak has the same issue.

Those other people you refer to...are they men without souls....zombies?

FL

[David Milisock]

Those other people you refer to...are they men without souls....zombies?

FL

I only know this I was buying printing from a company and for some unknown reason their color would just go bonkers, New Heidelberg install with service contract so all the configuration was part of the contract. Well afte about 3month they ask if I'd set in and observe the process. I suggested after my observations that theyrequest another technician, the second guy didn't dowell eithr but the third guy got it done.

Kodak never could get the Nextpress working so I finall calibrated it for them. I did several of these units they are unique.

[David Milisock]

I find this very confusing.

What do you mean by "media linierization"?

What do you mean by an "ink limit dot gain curve"?

TIC is a function of how an RGB to CMYK conversion is made. Not curves (plate or press).

thx, gordon p

People some times have a hard time understand that PS and ICC color management are much the same thing. Just like an ink jet media a press produces a different curve for each paper. So the plate is linerazed - printed to a media (paper) result is non linearized and read by densitometer/spectrophotometer- curve adjustments are made to plate setter - new curve printed - result read again until paper produces liner result with test.

During this process an ink limit is defined for each channel, it may be 86% DMAX and 2% MIN. 86 x 4 is 344 TIC When talking PS color management curves is a better term then profile this result will produce the color rendering dictionaries for the postscript interpretation process.

TIC is simply a term total ink limit, be it RGB to CMYK or CMYK to CMYK which is what PS color management was designed to work with ONLY!!

Is this stuff really a curve?

No, there is a LAB color model equivalent of the CMYK TIC 400 color model, PS CM systems assume this as the source space and for press purposes CMYK can be considered to be an absolute color space for the source.

The destination space is the space you created by the plate lineraization, ink limit process the TIC and curves also have through the software process a LAB color madel equivalent.

The plate making process simply connects the assumed color space with the descination color space via LAB.

Assume this, any ICC compliant application Adobe/Corel whatever, with a working CMYK of US web uncoated, anyone worth their salt knows this is a TIC 260 profile.

The designer uses a green C100 Y100 M5 K0, imports a CMYK image converted to the propper CMYK profile and produces a PDF for output, (if done correctly it will an uncolor managed PDF). As we read the green color all through the process it will read C100 Y100 M5 K0 and we all know the paper is not going to hold that ink however spot reading of the image show that its CMYK numbers are being passed along also.

Nothing in the ICC controlled process before the plate settter allows for the conversion to the plate destination color space for the non-images objects in the file.

The file is opened in lets say Super Trap and then trapped, then passed along to Signastation and imposed, still at all these points the CMYK numbers read just as they did in the native application.

From Signastation it is RIPPed VIA PS to the destination plate, asssumed source space to created destination space.

The display of the native application always tries to simulate what C100 Y100 M5 K0 looks like but no real change ever took place in the application to the green object, the image was already changed so the display (if calibrated) may be fine.

So the imaged passed through to the plate unchanged as the CMYK numbers were already in small destination space, the green objects was changed because most likely the paper was only going to hold less then the 100 for the C and Y channel. However the change was expected by the designer because their display had a simulation of a small destination color space.

I've never seen any plate for any CMYK job created in any other manner.