Computer Graphics with Photoshop

Author

Giclee PPi

John K

2004-09-13, 4:14 am

Hi group,

Is there any sort of formula that exists for how many PPI I should
figure for images that will be output as Giclee prints?

For example, for images destined for a printing press, as a general rule
of thumb I double the line screen, which in almost all my cases wouldn't
surpass 150 lpi, so my images are saved at 300ppi... That's the formula
I use.

Is there a similar formula for giclee printers depending on the output
size or the dpi of the inkjet printer? Is there a certain "optimal
point" where more PPI is overkill?

I'm asking because I may be preparing hundreds of images that will be
output (eventually) as Giclees, at different sizes. I don't know which
company will do the printing so "check with the company doing the work
to see what they want" isn't really a good answer. I figured I'd save
them all at 300ppi, but a guy I know said that is WAY overkill and I'm
wasting space and that 150ppi is all I'd ever need for Giclee no matter
what the size... Is he wrong?

I don't have much experience with Giclee printing, but I would think
that a big 4 x8' poster would need less resolution in terms of PPI than
a small 8 x10" that one would look at up close. Is this correct?

Thanks in Advance.

Chris Cox

2004-09-13, 4:14 am

In article <414506E2.8EB4A73B@nospamhotmail.com>, John K
<jkennospam@nospamhotmail.com> wrote:

> Hi group,
>
> Is there any sort of formula that exists for how many PPI I should
> figure for images that will be output as Giclee prints?

That depends on what inkjet printer you're using and what sort of
halftoning it does.
(Giclee == inkjet)

Chris

Odysseus

2004-09-13, 4:14 am

In article <414506E2.8EB4A73B@nospamhotmail.com>,
John K <jkennospam@nospamhotmail.com> wrote:

> Is there any sort of formula that exists for how many PPI I should
> figure for images that will be output as Giclee prints?
>
> For example, for images destined for a printing press, as a general rule
> of thumb I double the line screen, which in almost all my cases wouldn't
> surpass 150 lpi, so my images are saved at 300ppi... That's the formula
> I use.
>
IME that's a safe 'rule of thumb' but you can almost always get away
with less: 1.5x the screen ruling is almost always fine, and gives you a
better preview of the image's sharpness as reproduced. Beside wasting
space -- less of a concern these days than a few years ago! -- an
excessively oversampled image tends to lose sharpness in print. But
halftone screens are a very different animal from inkjet dot patterns.

> Is there a similar formula for giclee printers depending on the output
> size or the dpi of the inkjet printer? Is there a certain "optimal
> point" where more PPI is overkill?
>
> I'm asking because I may be preparing hundreds of images that will be
> output (eventually) as Giclees, at different sizes. I don't know which
> company will do the printing so "check with the company doing the work
> to see what they want" isn't really a good answer. I figured I'd save
> them all at 300ppi, but a guy I know said that is WAY overkill and I'm
> wasting space and that 150ppi is all I'd ever need for Giclee no matter
> what the size... Is he wrong?
>
For most images, on most inkjet printers that produce 'dithered' rather
than halftoned images (the printer's nominal resolution is relatively
unimportant), I agree that 150 ppi should be fine. For type or very fine
details you might see some benefit from going higher, say 200 ppi.

> I don't have much experience with Giclee printing, but I would think
> that a big 4 x8' poster would need less resolution in terms of PPI than
> a small 8 x10" that one would look at up close. Is this correct?
>
If the big poster is only intended for viewing at a distance, certainly.
(For something like a trade-show display that people can walk right up
to, you might want to be more generous.) I used to output film for store
displays that were produced by silkscreening: not the same thing as an
inkjet, but illustrates the principle. We'd output 175-lpi film from
300-ppi images, then the film would be enlarged by a "blowback" system
-- which I gather is basically a specialized overhead projector -- to
400% to make the screens. The resulting ~44-lpi (now in effect based on
75-ppi data) images looked just fine -- from at least two to three
metres away. An inkjet print of the same size, from a source of similar
resolution, would most likely look smoother than the results of this
process.

--
Odysseus

Bill Hilton

2004-09-13, 7:14 pm

>From: John K jkennospam@nospamhotmail.com

>Is there any sort of formula that exists for how many PPI I should
>figure for images that will be output as Giclee prints?

Do you know which printer model you'll be using?

>Is there a similar formula for giclee printers depending on the output
>size or the dpi of the inkjet printer? Is there a certain "optimal
>point" where more PPI is overkill?

Older LightJet laser printers like the 5000 lay down 12 dots/mm (res 12) which
comes to 304.8 ppi and this is optimal for them, anything higher gets resampled
down. You can also send them res 8 (203 ppi) and that will get sampled up with
very little loss in quality. Newer LJ printers are Americanized for 300 ppi.

Durst Lambda printers are rated at 400 ppi native and will also accept 200 ppi
and upsample.

Inkjets like say the Epson Pros (4000, 7600, 9600) are different in that
whatever you send them gets resampled to the printer's native rez, but no one
at Epson is on record as saying exactly what the ideal rez is. I've seen some
tests on vector-type patterns that indicate very small improvements in print
quality up to 720 ppi but most shops say 360 ppi is all you need, and some feel
that for large prints you can go as low as 200 ppi and still get very good
quality. 300 ppi seems to be the most common compromise but if you have more
native (ie uninterpolated) pixels like say from a drum scan of medium format or
large format film there's no reason not to go as high as 360-400 ppi,
especially for smaller prints.

>I figured I'd save
>them all at 300ppi, but a guy I know said that is WAY overkill and I'm
>wasting space and that 150ppi is all I'd ever need for Giclee no matter
>what the size... Is he wrong?

I'd definitely save 'em at 300 ppi instead of 150 ppi myself. But if it's
important to you to reduce the file sizes to 25% then run a couple of early
tests to see if the lower number is acceptable to you. I can definitely see
the difference between 200 and 300 ppi on 16x20" prints on my Epson 4000 for
example.

>I don't have much experience with Giclee printing, but I would think
>that a big 4 x8' poster would need less resolution in terms of PPI than
>a small 8 x10" that one would look at up close. Is this correct?

Absolutely.

>Thanks in Advance.

Good luck. Best advice is to send off a couple of test images for printing at
150 and 300 ppi and see if 150 is enough for your requirements.

Bill

Tacit

2004-09-13, 7:14 pm

>I figured I'd save
>them all at 300ppi, but a guy I know said that is WAY overkill and I'm
>wasting space and that 150ppi is all I'd ever need for Giclee no matter
>what the size... Is he wrong?

Yes, he is wrong...for some giclee printers. For others, 150 ppi is the limit
of the effective resolution.

Different giclee printers have effective pixel resolutions that range from 150
to 280 pixels per inch (or so). Above 300 pixels per inch at the final size,
you aren't doing any good, but there's no compelling reason to go below 300
pixels per inch.

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