Velocity Reviews

Velocity Reviews (http://www.velocityreviews.com/forums/index.php)
-   Digital Photography (http://www.velocityreviews.com/forums/f37-digital-photography.html)
-   -   OT: how many ipd for a poster this size? (http://www.velocityreviews.com/forums/t247879-ot-how-many-ipd-for-a-poster-this-size.html)

Asbjørn Bjørnstad 11-27-2003 02:02 PM

OT: how many ipd for a poster this size?
 

Biggest poster I've ever seen, I'm sure they don't use 300 dpi.

http://heim.ifi.uio.no/~asbjxrn/poster.jpg

The window-washers on the left gives an good indication of the size of
this poster. It actually wraps around the corner, so you only see half
of it on this picture, and while there is not really a picture on what
you see here, there is a newspaper picture on the other side. Not very
good quality, though.
--
-asbjxrn

Ray Murphy 11-27-2003 05:29 PM

Re: OT: how many ipd for a poster this size?
 

----------
In article <5o3cc9lxip.fsf@tva.ifi.uio.no>, asbjxrn@fimm.ifi.uio.no
(Asbjørn Bjørnstad) wrote:


>
>Biggest poster I've ever seen, I'm sure they don't use 300 dpi.
>
>http://heim.ifi.uio.no/~asbjxrn/poster.jpg
>
>The window-washers on the left gives an good indication of the size of
>this poster. It actually wraps around the corner, so you only see half
>of it on this picture, and while there is not really a picture on what
>you see here, there is a newspaper picture on the other side. Not very
>good quality, though.
>--
> -asbjxrn


RM: There would be no need to use 300 ppi Tiffs to produce the
computer artwork -- here's why:

Huge posters - whether they are silk-screen printed or laser printed,
are first made in the normal way for viewing at a normal reading
distance. This would usually mean creating the (continuous tone)
graphics with say 300 ppi Tiffs and printing at 150 Lines Per Inch
(That's the half-tone dots of various sizes and shapes you see in
professional printing).
When the colour proof or "visual" is approved by the customer, a copy
of the image is then enlarged to the required size and the halftone
dots are made bigger, but we don't see them as huge dots because we
are so far away.

You can see this if you look at huge poster on the side of a bus. The
screen ruling for the pictures may have originally been 150 lines per
inch on the original proof, but the screen ruling may be only 15 lines
per inch on the bus.

Look at it this way - if you saw the original artwork for a bus poster
on an A4 sheet folded in half lengthways, it would make a long strip
105 mm x 297 mm, and it was enlarged 10 times, then the image would be
1050 x 2970mm (1 x 3 metres). That would make the 150 line screen into
a 15 line screen.

Now in the case of screen printing (for bus posters) this coloured
image is screened AGAIN in order for the 4 colour printing process to
print the poster in CMYK (Cyan, Magenta, Yellow, Black). So the four
passes through the screen-printing machine will reproduce the FOUR
colours in the poster. The same would happen if it was done on an
ordinary offset press if it was big enough. Theoretically this extra
screening should not be necessary, but that's the way it's done.

In the case of digital output (laser printing onto huge poster rolls)
the same thing must happen. This means that the huge laser printer is
provided with a huge computer document with the re-screened image on
it. This is done by making the screen ruling coarser in a direct
relationship to the enlargement involved.

You could actually make your own example of this by making a tiny
piece of coloured artwork with your inkjet say 20 x 20mm of say a red
rose and afterwards simply enlarge your computer document of the rose
image to 1000% (200 x 200 mm) and then change the number of pixels to
30 per inch and print your job with a 15 Lines per inch screen. (You
need 2 pixels for every halftone dot).

This will give you VERY clear (in fact huge) halftone dots, but your
laser printer or inkjet is working normally.
After the job is done, just hang it on the wall and take several steps
back and you will see no halftone dots, but the rose will look just
the same as when it was only 20mm square.

Ray
















All times are GMT. The time now is 12:46 AM.

Powered by vBulletin®. Copyright ©2000 - 2014, vBulletin Solutions, Inc.
SEO by vBSEO ©2010, Crawlability, Inc.