Lpi dpi, ppi

[pacificiam]

Hi,

Any1 can tel me that what is the relation between LPI, DPI and PPI?

As per my knowledge DIP=2*LPI.

Is i am correct??
If not den correct me.

I know its really silly question

But i gt confuse in it

 

[Lukas Engqvist]

Gordo has some good posts on this. It really depends on the type of raster, and if we are to be very picky about the image itself.. but I don't think that's the convenient answer.

Look at http://printplanet.com/forums/digital-printing-discussion/22970-can-someone-explain-dpi
http://printplanet.com/forums/prepress-workflow-discussion/24625-resolution-factor/2

but this is the best place since it shows what it talks about
http://qualityinprint.blogspot.com/search/label/lpi/dpi

 

[Correct Color]

There shouldn't be any correlation between DPI and LPI, because they're describing two different things.

LPI is Lines Per Inch. Typically, it's a measure of the fineness of a halftone screen. Halftone meaning that the dots in the image can be anywhere from 0 to 100 % of their addressable area. This is typical of traditional litho printing where you might think of a 5% do, or a 50% dot, or a 95% dot.

DPI is Dots per inch. Typically it's a measure of dots in an area where the dots are all the same size. Or if not the same size--as there are some variable dot printers--at least that the size of the dots is not determined by the image they're reproducing. So instead of an area using a traditional halftone screen making a shadow are by creating 95% dots, in this type of screening method, you'd have 95% of the area full of equal-sized dots.

However, both LPI and DPI do refer to ink. They refer to the smallest amount of individual colorant a particular printing device is putting down per primary.

PPI doesn't refer to ink or printers at all. PPI is Pixels Per Inch. And what a pixel is--for digital purposes--is the smallest area of complete color information in a digital image.


Mike Adams
Correct Color

 

[gordo]

There shouldn't be any correlation between DPI and LPI, because they're describing two different things.

"DPI" is a term used for a variety of things that properly speaking it shouldn't (e.g. the resolution of a CtP device, the pixel density of a raster image, a scanner's resolution, etc.). So it's always best to define one's meaning before asking, or answering this type of question.

The important thing is that if the relation between the dpi/ppi/spi of the raster image is too low relative to the lpi/dpi of the imaging device then there is a likelihood that the individual pixels of the image will be imaged clearly enough to be seen in the final reproduction. Which is usually not desirable. This is one reason why images downloaded from the interwebs that is at 72 dpi/spi/ppi are not appropriate for printing at 150 lpi (which defines the resolution of the presswork).

best, gordo