"He who marches out of step hears another drum." ~ Ken Kesey
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.
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?
Quote from: Orion on April 20, 2011, 10:35:32 AMPierre, 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.
Quote from: drdot on May 05, 2011, 11:50:14 AMQuote from: Orion on April 20, 2011, 10:35:32 AMPierre, 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.
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.
My brain just exploded.
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 . . .
Quote from: blue moon on May 05, 2011, 12:04:47 PMI 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.