really? Do you mean 300dpi resolution of a platesetter or ppi picture resolution?My standard is 175 -200 lpi with 300 dpi
300 DPI for images in files and 2,540 DPI Dot per inch for Ctp...Thank you very muchreally? Do you mean 300dpi resolution of a platesetter or ppi picture resolution?
sorry, i am not awakend enough in this morning to do the math with inch and mm... ;-)
You will find some - if not all -answers here on Gordo´s site:
The Print Guide
How to calculate halftone dot sizes in microns
or in this (maybe a little bit dusty?) booklet for free:
View these points in all there:
- 256 gray levels/supercells
- common limit of usually needed size 20 μ (=0,002 mm) for a smallest dot-size for offset-printing technology with plates
- the fact, that the human eye is not able to see more details than a resulution of about 300ppi whithout any help of glasses at a distance of about 25-30 cm between the eye and a print for making sure that all your maths making sense... ;-):
(A formula for determining a usable, optical (!) "Minimum" image resolution is based on the viewing angle of the human eye (constant) at the point where an observer still has two points at a certain distance (variable 1 = sought "image resolution" ") can be differentiated / resolved depending on the viewing distance (variable 2).
This is done using a triangle calculation using the rule of three with an angle function (tangent)
Unfortunately, the constant - the viewing angle - is controversial or cannot be documented uniformly, especially since it is also subject to different eyesight, Wikipedia speaks of a minute of arc (roughly 0.0167 °)
Tangent angle alpha is the sum of the division of the opposite side by the adjacent side, where the opposite side is the image resolution sought and the adjacent side is the viewing distance. So you multiply the tangent of 0.0167 ° (which is then the value 0.0002915) by the viewing distance.)
No contradiction here. The last place I worked printed everything with 300LPI hybrid screening (Stochastic below 5% and above 95%) We let 300ppi images go, and found there are very few instances where extra resolution was helpful.... if a human can not see a difference between 300 and 450 ppi whithout any help like glasses...
Contradiction is welcome ;-)
Here's an uncomplicated way to look at it.Hi. My standard is 175 -200 lpi with 300 dpi. If I want 250 lpi which dpi recommended ?
Another is how big dot sizes at 3% 250 lpi compared to 175 lpi and 200 lpi? Thank you
3% dot width um = 25.4 , 22.3, 18.0
Sorry Sir . Where are come from ?
Thank you very much250 lpi = 98,43 lpcm (=rounded 100 lpcm)
-> 10 lines per mm -> 1 line per 0,1mm
-> width of 1 line = rastercell is 0,1mm
->1 rastercell has 16x16 squares, because
8Bit (28=2x2x2x2x2x2x2x2)=16x16=256 different tonevalues,
the width of 1 square is (0,1mm rastercell/16=) 0,0063 mm
CMYK range 0-100% = 100 steps but 101 different values of cyan in range 0-255=256 different tonevalues
that leads to:
1% tonevalue cyan means 2,53 squares of/in 256 different tonevalues,
so 3% means (3x 2,53=) 7,59 (rounded up = 8) squares of 0,0063 mm width in a sheme three horizontal and three vertical what means also 3x 0,0063 mm = 0,019 mm (rounded up from 0,0189 mm = 18.0 um...)
View attachment 290368
next math is how to match this with the resolution of the different devices (1200dpi, 2400 dpi, 2540 dpi, 3000 dpi, 4000 dpi)
2540 dpi means 1000 dots per cm -> 100 dots per mm -> 10 dots per 0,1 mm and as smallest size 1 dot per 0,01 mm -> 10 um, because no good RIP will generate and no device will write only one dot (double signal rate...!) also a 1% tonevalue Cyan will be written with two or three squares and 2x 0,0063 mm = 0,0126 two square width will fit with 0,01mm smallest dot size but would be written with 2 dots with 0,02mm either in heigh or width...
Thank you sir256 different tonevalues divided through 101 (cmyk range 0% to 100%=100 steps but 101 values) = 2,53
You can work just with 100 also for what you are looking for.
And may be it is one step more correct if you take 257 because 16 x 16 = 256, but there is also to add a zero to 256 possible squares(=dots) i think, but than it does not fit so nice to the range 0-255 in photoshop anymore... ;-)
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