halftone measurment results. WOW, dot gain galore!

[blue moon]

So I printed some films today and measured the dots on the film. To no surprise, the FIlmMaker shined again and white it was off, it was in 2%-4% range. Much better than the two other RIPs I used previously.

Next step, I burned my crappiest 305, set the squeegee to 4 (on a 10 scale) and floodbar on 2 (again 10 scale). 70 duro (single) blade.

Printed the test pattern and Holly Batman! to dot gain is crazy!!!
 5% reads 17%
10% reads 27%
50% reads 72%
75% reads 83%
and 95% actually reads 95%.

looking at the curves in the RIP they actually adjusted the top end so I am not surprised that it is right on in the uppers, but 20% out in the middle?
Now this is not the issue with a RIP as it obviously created good films.

So I can go into the settings and set up an adjustment curve, but am worried that I might no be laying down enough ink if I do that. As it is, my old RIP used to print the 50% dot at 64%, so that means it was an 85% or so before. If I go and tweak it down to 50% I will be removing 40% of the ink being laid down. That scares me! There is not going to be much left on the shirt at that point . . .

Does anybody have any experience with this? Am I crazy for even worrying about it? or am I crazy for even asking and should go and remap that curve?

pierre

[squeezee]

If you want to print 50%, move the curve so that you get 50%
You might find that the shirt looks flat compared to the usual because we are used to colours getting 'popped'.  If you looked at a cookery book with realistic colours it wouldn't appeal so they saturate the colours.
I don't understand the rest of the post? Filmmaker films were within 2-4% of their target?  That gave dot gain on your press?
You just need to set up your RIPs properly.

[Orion]

Pierre, if you printed a 50% dot that gained to a 72%, that is not a 20% gain it is 44% gain. Yep, you need to go back in the rip and adjust the curves. I don't understand the amount of dot gain that you are experiencing in the lower percentages, the numbers aren't making sense to me. How hard are you flooding your screen?

[blue moon]

If you want to print 50%, move the curve so that you get 50%
You might find that the shirt looks flat compared to the usual because we are used to colours getting 'popped'.  If you looked at a cookery book with realistic colours it wouldn't appeal so they saturate the colours.
I don't understand the rest of the post? Filmmaker films were within 2-4% of their target?  That gave dot gain on your press?
You just need to set up your RIPs properly.

Dave,
nothing wrong with the RIP all the gain is press related!

Yes, I was worried that if everything is adjusted, prints would not look as good (less color and less coverage) as they do now.
I just might have to create another profile and test it . . .

pierre

[blue moon]

Pierre, if you printed a 50% dot that gained to a 72%, that is not a 20% gain it is 44% gain. Yep, you need to go back in the rip and adjust the curves. I don't understand the amount of dot gain that you are experiencing in the lower percentages, the numbers aren't making sense to me. How hard are you flooding your screen?

I am flooding pretty hard, and certainly can adjust it both on the press and in the RIP.

re: lower percentages. So when I print the film and it is supposed to be 5%, it might be a few points off. So lets say, the 5% dot prints as an 8% and then at the press it gains to 17%. That's 200% more coverage!!!

Trying to read the dots on a shirt is not quite exact science, there was a lot of fluctuation. I was just surprised to see how much dot gain there is!

pierre

[yorkie]

Let me try to explain the "zen" of dot gain.

Start off by clearing your mind and listen to the press. Imagine the press as a stack of speakers and press calibration is the mixing board. If the speakers are in a small room, the dials need to be tuned down, where in a large room, the dials turned up. If the walls are marble, then some frequencies need to be turned up or down, verses if the walls are carpeted. The speakers (the press) does not get to choose the conditions it will be playing (screen lpi, textile fabric, squeegee pressure, ink viscosity...).

The way to calibrate a press is by starting off by setting all of the knobs the the middle position. In the case of squeegee pressure, find a nice middle setting, that should all else fail, you still can adjust the darkness to be a little darker or a little lighter. If everything else described works perfectly, the pressure setting of the press should never change.

The postscript language used in RIP's (Raster Image Processors) was actually designed by printers!!! The computer screen should display a reasonable representation of the data in the graphic file, but when output to film, the image is transformed to a value which is correct for the press. The simplest example is negative film. This is simply a reversal of the calibration values.

The actual calibration values are very simple. 0.0 represents white, 1.0 represents black, .1 is 10%, .2 is 20%... this gives an array of numbers

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

If the 50% screen is actually 70%, then the value in the array would need to be a .3.

0.0 0.1 0.2 0.3 0.4 0.3 0.6 0.7 0.8 0.9 1.0

Inside photoshop, these values are expressed as a graph.

These basic values are inherent in postscript. There are multiple ways to access these values. The value can be adjusted in photoshop (as attached), these values can be invoked via color correction adjustments in the artwork, the values can be embedded in a .ppd file and accessed through a print driver, the values can be set within the rip... Any and all of these methods can either act cumulatively or absolution, depending on context. In simple words, changing a .5 to a .3, could be multiplied by a .97% somewhere else such as color correction via color space.

Quite often the simplest way to control press gain, is to turn off all other forms of gain control, except the one you control. Don't color manage the file!

For my purposes, photoshop is the easiest place to control the calibration curve. various curves can be stored is setup files to photoshop.

The other easy place to control the calibration curve is via the rip, but typically to control the calibration curve in the rip, is by setting up multiple print queues. Different print queues can define different mesh/lpi/ink combinations. This can mean a LOT of queues, but with good naming is manageable.

Beyond the numbers exists reality. A 5% screen if very difficult to print, so calibration files often bump the low end. T-shirts also look great with "BIG COLOR", the heck with correctness, we want it popping! The translates to a smaller spectrum of tone being used to represent the entire spectrum. So long as in a fountain fill, the dots make a smooth transition, more is often better. :\

The place to begin controlling for gain, is by printing a test pattern, which includes a graduated screen and individual percentage blocks. Turn off all control and see where on the graduated pattern the dots first appear and where the dot pattern disappears. Test different press settings to see what gives the widest band of small dots to no dots. For manual printing, test 2 easy on the arms strokes verses what various levels of muscle will produce. Remember, you want to make it easy on yourself and on the machine!

Test a couple exposure settings and be sure the exposure is where it works best. Again, this should be the natural value of the light curing the screen. Where washout is easy, but crisp. A value which produces consistent results. A value which washes out the smallest of dots...

Once the press, exposure and washout are a constant, then adjust those 11 values to produce a piece of film, which yields the desired printed results (correct or purposely incorrect).

[drdot]

Pierre, if you printed a 50% dot that gained to a 72%, that is not a 20% gain it is 44% gain. Yep, you need to go back in the rip and adjust the curves. I don't understand the amount of dot gain that you are experiencing in the lower percentages, the numbers aren't making sense to me. How hard are you flooding your screen?

This is incorrect. There are two ways to measure dot gain and by far the most common is using the Murray-Davies calculation where dot gain is reported in absolute percentages, not relative. So in this example, the dot gain is 22%. If it were 44%, the 50% dot would measure 94% on the printed surface. I should also point out that there are two different types of dot gain, mechanical (physical) and optical. My reply here  is based on the mechanical component, although optical gain is also simultaneously occurring.

When mechanical dot gain is described, it is always measured at the 50% value using Murray-Davies equation. In order to get an accurate value you must know the starting and ending density values of your ink. This means zero to the value of the print surface and measure the value of the solid ink. You are calibrating based on what a 50% DOT AREA actually ends up. This means you need to measure with a spectro-densitometer if doing sim process or a color reflection densitometer if doing 4 CP.  There are only a few of us crazy enough to invest in these measuring devices as they are all over $1000 and some as much as $4500. 

Dot gain occurs as the perimeter (border) of the dot grows. This is based on Zone Theory (also called Border Theory) based on the mechanical growth of the dot due to ink spread. For any given linecount, the increase in the dot gain will be constant to the perimeter. So, if the gain is .001" (made up example) increase around the perimeter, it will be the same for every percentage of dot. Since the maximum perimeter occurs on the 50% dot, it will have the lowest relative gain. The very small highlight dots can easily double or even triple in value  (eg 5% dot becomes 10% -15%) As the halftone dot gets larger, the amount of gain will decrease as both an absolute and relative percentage.

We can cheat the systems somewhat by changing the dot shape and how the dots connect across the tone range. This is why we use elliptical dots to give us the most control over the tone transitions and to minimize the effects of mechanical dot gain.

Like most things in this business, the vast majority of printers "eyeball" their results by comparing their printed values to some type visual reference. This is fine as a general rule, but the problem comes when different colors (pigments) have different dot gain profiles.  This means the printer must know how each color will behave and adjust accordingly.  This is also one of the main reasons it's  almost impossible to get a dead-on color match when you need to hit a measured color like a Pantone color. It can definitely be done, but it's outside the realm for 99.9% of t shirt printers. Thankfully there are not that many jobs that require this level of accuracy.

[Clark]

Pierre, if you printed a 50% dot that gained to a 72%, that is not a 20% gain it is 44% gain. Yep, you need to go back in the rip and adjust the curves. I don't understand the amount of dot gain that you are experiencing in the lower percentages, the numbers aren't making sense to me. How hard are you flooding your screen?

This is incorrect. There are two ways to measure dot gain and by far the most common is using the Murray-Davies calculation where dot gain is reported in absolute percentages, not relative. So in this example, the dot gain is 22%. If it were 44%, the 50% dot would measure 94% on the printed surface. I should also point out that there are two different types of dot gain, mechanical (physical) and optical. My reply here  is based on the mechanical component, although optical gain is also simultaneously occurring.

When mechanical dot gain is described, it is always measured at the 50% value using Murray-Davies equation. In order to get an accurate value you must know the starting and ending density values of your ink. This means zero to the value of the print surface and measure the value of the solid ink. You are calibrating based on what a 50% DOT AREA actually ends up. This means you need to measure with a spectro-densitometer if doing sim process or a color reflection densitometer if doing 4 CP.  There are only a few of us crazy enough to invest in these measuring devices as they are all over $1000 and some as much as $4500. 

Dot gain occurs as the perimeter (border) of the dot grows. This is based on Zone Theory (also called Border Theory) based on the mechanical growth of the dot due to ink spread. For any given linecount, the increase in the dot gain will be constant to the perimeter. So, if the gain is .001" (made up example) increase around the perimeter, it will be the same for every percentage of dot. Since the maximum perimeter occurs on the 50% dot, it will have the lowest relative gain. The very small highlight dots can easily double or even triple in value  (eg 5% dot becomes 10% -15%) As the halftone dot gets larger, the amount of gain will decrease as both an absolute and relative percentage.

We can cheat the systems somewhat by changing the dot shape and how the dots connect across the tone range. This is why we use elliptical dots to give us the most control over the tone transitions and to minimize the effects of mechanical dot gain.

Like most things in this business, the vast majority of printers "eyeball" their results by comparing their printed values to some type visual reference. This is fine as a general rule, but the problem comes when different colors (pigments) have different dot gain profiles.  This means the printer must know how each color will behave and adjust accordingly.  This is also one of the main reasons it's  almost impossible to get a dead-on color match when you need to hit a measured color like a Pantone color. It can definitely be done, but it's outside the realm for 99.9% of t shirt printers. Thankfully there are not that many jobs that require this level of accuracy.

Huh?





No, really this is awesome stuff Mark..thanks for contributing.

[blue moon]

Pierre, if you printed a 50% dot that gained to a 72%, that is not a 20% gain it is 44% gain. Yep, you need to go back in the rip and adjust the curves. I don't understand the amount of dot gain that you are experiencing in the lower percentages, the numbers aren't making sense to me. How hard are you flooding your screen?

This is incorrect. There are two ways to measure dot gain and by far the most common is using the Murray-Davies calculation where dot gain is reported in absolute percentages, not relative. So in this example, the dot gain is 22%. If it were 44%, the 50% dot would measure 94% on the printed surface. I should also point out that there are two different types of dot gain, mechanical (physical) and optical. My reply here  is based on the mechanical component, although optical gain is also simultaneously occurring.

When mechanical dot gain is described, it is always measured at the 50% value using Murray-Davies equation. In order to get an accurate value you must know the starting and ending density values of your ink. This means zero to the value of the print surface and measure the value of the solid ink. You are calibrating based on what a 50% DOT AREA actually ends up. This means you need to measure with a spectro-densitometer if doing sim process or a color reflection densitometer if doing 4 CP.  There are only a few of us crazy enough to invest in these measuring devices as they are all over $1000 and some as much as $4500. 

Dot gain occurs as the perimeter (border) of the dot grows. This is based on Zone Theory (also called Border Theory) based on the mechanical growth of the dot due to ink spread. For any given linecount, the increase in the dot gain will be constant to the perimeter. So, if the gain is .001" (made up example) increase around the perimeter, it will be the same for every percentage of dot. Since the maximum perimeter occurs on the 50% dot, it will have the lowest relative gain. The very small highlight dots can easily double or even triple in value  (eg 5% dot becomes 10% -15%) As the halftone dot gets larger, the amount of gain will decrease as both an absolute and relative percentage.

We can cheat the systems somewhat by changing the dot shape and how the dots connect across the tone range. This is why we use elliptical dots to give us the most control over the tone transitions and to minimize the effects of mechanical dot gain.

Like most things in this business, the vast majority of printers "eyeball" their results by comparing their printed values to some type visual reference. This is fine as a general rule, but the problem comes when different colors (pigments) have different dot gain profiles.  This means the printer must know how each color will behave and adjust accordingly.  This is also one of the main reasons it's  almost impossible to get a dead-on color match when you need to hit a measured color like a Pantone color. It can definitely be done, but it's outside the realm for 99.9% of t shirt printers. Thankfully there are not that many jobs that require this level of accuracy.

Huh?





No, really this is awesome stuff Mark..thanks for contributing.

aaaah, few more things make sense now (the high gain in lower percentages)! FWIW, I did go ahead and purchase a refl/trans densitometer and it was used to take the readings straight of the shirt. The readings were very erratic, due to the weave interference and I am certain that the measurements were off a little.

All of the RIPs and even Photoshop have the adjustment curves to compensate for the dot gain. Those are easy to use and set up if a densitometer is available.

I guess I answered my  next question in my head as I type. Should I correct and suffer low ink coverage? I am thinking, yes, and then adjust up as needed. Better to know and adjust than eyeball . . .

Thanx for sharing Mark!

pierre

[Dottonedan]

@DrDot.

This is also one of the main reasons it's  almost impossible to get a dead-on color match when you need to hit a measured color like a Pantone color. It can definitely be done, but it's outside the realm for 99.9% of t shirt printers. Thankfully there are not that many jobs that require this level of accuracy.

HA!  You haven't watched those Mickey Mouse artist creating that vector art file with 60pms colors and them wanting the printer to match each pms color exactly. HAHA. Just like Santa Claus said about those little M&M characters. "They do exist".

Excellent food to chew on!  Good food. "Food for thought" as they say.

Thanks
Dan

[Command-Z]

My brain just exploded.

[ftembroidery]

My brain just exploded.

The only reason mine didn't is because the holes in my head let off the excess pressure......but you should have heard the WHISTLING sound that was emanating from me.

Edited because of a spelling error

[yorkie]

I guess I answered my  next question in my head as I type. Should I correct and suffer low ink coverage? I am thinking, yes, and then adjust up as needed. Better to know and adjust than eyeball . . .

Your prints look good, don't mess that up just to make a machine read some number. The fact that the 95% is 95% and not 100%, tells me that something is controlling the press gain. My question is to what extent you understand what is actually happening? If you print process, do you get similar numbers? When you underbase in white, do you get similar numbers.

The most simple of tests is a graduated screen, which runs from 0% to 100%. Where in the halftone does it first leave a mark and how far up can you still see a halftone? Different inks have different characteristics.

[blue moon]

I guess I answered my  next question in my head as I type. Should I correct and suffer low ink coverage? I am thinking, yes, and then adjust up as needed. Better to know and adjust than eyeball . . .

Your prints look good, don't mess that up just to make a machine read some number. The fact that the 95% is 95% and not 100%, tells me that something is controlling the press gain. My question is to what extent you understand what is actually happening? If you print process, do you get similar numbers? When you underbase in white, do you get similar numbers.

The most simple of tests is a graduated screen, which runs from 0% to 100%. Where in the halftone does it first leave a mark and how far up can you still see a halftone? Different inks have different characteristics.

Oh, yes, there is plenty more for me to learn and test. This was just a quick test on a tired old static 305. I used a plain 70 duro squeegee (normally use 80 or triples for stuff like this). no idea what will happen when I test the other ink types.

THe RIP actually has a built in curve for the top percentages, thus the 95 reads 95. THe 100 was not as black as I'd like it to be. The screen was completely open, but the coverage was not as good as I'd like it to be. So as I said, this was just a quick test and the results were very surprising.

My thinking is . . . If I get the 50 to print as 50, I can then adjust the curve back to where it needs to be to get the brighter colors or better coverage. This way I would know what is going on exactly and the results would not be a surprise.

pierre

[Chadwick]

 
You folks kill me.