The 1.5 ppi to 1 lpi is for photographic images only.
if you were to print a photograph one image at 1.5 to 1
and the identical image at 2 to 1, you would be hard pressed to tell which was which.
And I agree vector art should be vector art and it will look much better left that way.
We all should know that there are always exceptions to every hard and fast rule. Those of us who have been working in the industry for some time now know when we can break those rules and get away with it. Newcomers who don’t have this understanding don’t, and shouldn’t until they have a complete grasp of the situation.
OK, I found the formula in Adobe’s print publishing guide It’s copyrighted up to 1995, so the data is getting old. But this should help beginners.
The formula is :
(Output resolution / screen ruling)2 + 1 = shades of grey
maximum # of shades of grey = 256
Example: (1200 dpi / 90 lpi)2 +1 = 178 shades of grey
Since I couldn’t remember how to format formulas via html, I will spell out the formula so there is no misunderstandings.
(Output resolution in dpi divided by screen rulling in lpi) to the second power plus 1 equals how many shades of grey are available.
Hope this helps and I hope this is still applicable.
Silk
Silk you are confusing ppi with dpi.
Works with rhinestones here.
Len’s giving bad advice, people.
Maybe at 175# you can "get away" with this formula, but at 85# you’re living in a dream world if you think 120 ppi will carry the same detail screened as 240 ppi. I’m looking at my HP output and I can see a break from 160 (2x) to 320 (4x). I must be Superman.
SM
You obviously do not understand the reasons why any over-sampling is necessary, SM.
If one could be certain that the image raster and the screen were perfectly aligned *NO* oversampling would be required at all, and all additional data would just be discarded. 175 ppi would be the perfect, ideal images rez for a 175 lpi linescreen.
Unfortunately when that does not occur, some data will be ‘lost’ -i.e not align with the screen, and so we need to over-sample to ensure there is data available to the screen. An over-sampling of 1.4 is quite sufficient to ensure that that situation exists.
The reason I use 2xLPI is quite simply that it actually decreases RIP time (trust me, your output bureau will love you). Imagine a RIP having to divide everything by 2, or having to divide by 1.65, creating ‘super-scalar’ numbers that have to be rounded out.
Buko – 6:55am Oct 30, 07 PST (#61 of 64)
Silk you are confusing ppi with dpi.
Nope, As I mentioned the book was written in 1995. DPI is the term used in the book. I did not alter anything.
The book specifically states DPI for Output resolution. In fact on the previous page it states the image on a monitor is PPI and on an output device it is DPI. They even have image of a 300ppi @ 1200DPI go figure. Its on page 16 and 17 if you happen to get that book. Mine came with Pagemaker.
Silk you are confusing ppi with dpi.
I stand by my statement.
Pixels per inch (ppi) is the resolution of the file. This has nothing to do with dots per inch (dpi) which is the resolution of the printer. Lines per inch (lpi) is the resolution of the screen that is printed. What we are talking about in this thread is the relationship between ppi and lpi and has nothing to do with dpi.
An over-sampling of 1.4 is quite sufficient to ensure that that situation exists.
exactly!
Even Adobe documentation sometimes mixes ppi and dpi as if they were interchangeable.
"When I use a word", said. Humpty Dumpty, "it means just what. I choose it to mean … neither more nor less."
In this instance though the term was being used correctly its silk who is confused.
JJ/Buko, unfortunately they do cross-over at some points where they are inter-changeable.
You have to remember some of us come from the day that there was only one term DPI. I don’t plan on pushing the issue, because I know there are members of this forum who are more qualified than my self. In the end the quality of the image will be the lowest common denomitator.
Silk