DPI/Resolution/Dimensions query

[kev@frames]

One for our print experts:

Printing company asks me for a 300 DPI jpg.

what exact dimensions in pixels would the images need to be to print at 300 DPI as an A6 and an A5 respectively?

[kev@frames]

sorry, what i should have asked while there was still editing time: is it as straightforward as this?

eg.
if A5 = 210x148 mm (4.134 x 5.826 inches)
do I simply require an image 300 x 4.134 = 1240 x 300 x 5.826 = 1748 for an A5?

eg. a 1240x 1748 jpg printed at A5 is 300 DPI?

Is this the right way to work this out? Googling has some confusing and conflicting "answers".

[JohnMcafee]

You got it right, Kev.

A5 paper dimensions 148mm x 210mm (5.83" x 8.27")
at 300 DPI - 1748 pixels x 2480 pixels (print resolution)


A6 paper dimensions 105mm x 148mm (4.13" x 5.83")
at 300 DPI - 1240 pixels x 1748 pixels (print resolution)

[kev@frames]

thanks john! framers forum to the rescue again

[stcstc]

you cant make a 300DPI file, its 300PPI, if the print company ask for DPI its cos they dont know what they are talking about!!!!

if you look in photoshop u will notice its pixels per inch NOT dots per inch

[kev@frames]

maybe they have dumbed it down for us members of the public steve? I've never heard of PPI, although DPI is as old as the hills.

eg. DPI is dots per inch on the litho print colour - the printed output? (dots per inch) and PPI is the pixels per inch in the file. so I send my file to be printed at 300DPI and they can print the 300PPI file at the right size for an A5/A6 depending on the number of pixels x/y in the file. if they print at 600DPI my printed image is half the size (for example). Seems to amount to the same thing (?)
Thanks for the input. I see what you mean.

[stcstc]

yea DPI is an output term, well actually a term for scanning too

but files are always ppi,

the dpi ppi always gets misused

anyway yes you explanation is correct although technically you can do other things for example the the rip i use for printing expects 360ppi, which is the native resolution of epson printers (well kind of) so for example if you gave me a file which was 360ppi for A5 say

the long side is 210mm or 8.5 inches (ish) = so number of pixels is 8.5 * 360 = 3060 pixels

but i could print it say 17" wide and get the rip to interpolate the pixels, and at those kind of sizes with a decent file to start with you wouldnt tell the difference

[Tim]

Mr Pedant here, but most A5 papers and cards will be 210 x 148.5mm, not 210 x 148 (since they'll be made by cuttting a sheet of A4 in half) so your image will be 5 pixels/dots too small in the smaller dimension.......

[stcstc]

also if its a photo it wont generally be the right shape for a5

[kev@frames]

I'll just make it to suit the size they state their paper is Tim who knows what sort of cutting machinery they use or tolerances in the paper/cutting.

pedantry can be interesting and educational.

I just now realised where the name of steve's business came from No steve its not a photo by the way. those sizes are a whole other can of worms eh!

I used to work in a litho printers, we never had PPI in those days, but plenty of DPI, all the plates were made from a camera, no digital files at all. Just stored in filing cabinets as actual size negatives to print the plates off. One of each of the four colours. I guess the file requirements are the digital age equivilant of "camera ready-actual size" artwork.
Jeez, now i feel so old

Thanks guys for all the advice. much appreciated.

[JohnMcafee]

When a client does not supply you with the dot size, it is pretty much common sense to assume that he means dot=pixel.