Sending files for printing

[DJ]

Whilst you agree with me about the irrelevance of image resolution until printing, it appears that you have fallen into the trap of using dpi and ppi interchangeably. The figures that you have quoted above are dpi values, not ppi. A printers output resolution is measured in dpi. ppi is an attribute of a printed image, not a printer.

Not so Steve, they are PPI, we're not talking about output resolution with those figures, we're talking about the "raster" resolution, which is the driver's native "input" resolution, which is measured in PPI. This resolution is decided by which "output" resolution you choose. For example, if you choose 2880dpi output resolution, the raster input resolution used in the driver is 720ppi ( on say an Epson 2400 ), and that's what those figures relate to. We're still dealing in pixels at this stage, we haven't got to dots yet

PPI is an input resolution, DPI is an output resolution, a printer driver has two sides, input and output.

[Joanna Carter]

Ok DJ. I took some time last night to run some empirical (suck it and see) tests .

First, I took a 4x5 trannie and scanned it at 3200ppi which, with edge losses, gave an image that was about 31cm*38cm at 720ppi. Then I rescanned at 1200ppi which gave me approximately the same size image at 240ppi.

I then sharpened both images and applied the same curve to both images. Upon printing them, there was only the barest of differences between the two and what extra clarity there was was in the 240ppi image.

So, it is my considered opinion that the resolution for printing really doesn't make any difference worth the extra effort and disk space required by the higher resolution. Which follows the wisdom received from those those who taught me as well as the books on Photoshop that I have read.

[Rob Lycett]

Hi
I worked for 6 years managing a design dept for an exhibition display company. We had 3 60" 6 colour piezo pigment printers to operate. They were 720 dpi printers. One of them was able to do 1440. Imagine that, 1440 dpi over 60 inches media width!

We never saw any improvement in quality by having digital files at that same resolution. We did experience time delays from the huge file sizes though. We always worked at half (360) and quarter (180) resolution. If clients supplied higher res scans we downsampled them. Print quality was more affected by good scans - good tonal range, not over sharpened, good original trannie/print.

Viewing distance also becomes a factor. I did a building wrap once where the resolution of the image was 8 ppi. The printer was running at 16 dpi. From 50 yards the image looked as good as an 8x10 Ciba at 20 inches.

Just before I left that job to go into design teaching, we were using pdf files in our workflow - so all images were jpeg compressed.

The obsession with resolution as a measure of quality is probably taking your eye off the ball (like the obsession with processor speeds in computers). I have a 2 megapixel Nikon Coolpix 950 which produces much nicer images than many a 6 megapixel camera around today. The difference is the metering (matrix or spot) and lens quality of the Nikon, not the theoretical density of the CCD.

So for piezo inkjet print lower resolution should be fine (test first). For litho printing, when an image is halftone sceened, your scans should be at 1.5 - 2 times the resolution of the screen. So for halftones at 133 lpi (typical of most magazines) your scans will be around 200 ppi. The reasons for this are far too complicated to attemt an explanation now.

[DJ]

Fair enough! Like I said, once you know the process and what the driver is actually doing, you can perform these tests for yourself, and decide the real question, whether it's worth the effort or not. In the end we all have different eyeballs, and it's a subjective evaluation for us all, and being able to decide for yourself is the best way IMHO.

For what it's worth, I don't use 720ppi myself, I use 360ppi, and I just accept that the driver is going to interpolate it to 720ppi, and probably render the sharpening slightly less effective.

I personally am going to stick with large files and the information from the programming manuals, this way I know that I have controlled every aspect. I must be a control freak. As I said, the difference will be subtle, not night and day, but there is a difference. If all it's costing me is a little time and disc space, I'm ok with that, and I won't have to scan the blasted things more than once.

I honestly think a lot of the stuff in books and on websites is based on outdated knowledge, it seems to follow the wisdom from 10 years ago when I worked in the newspaper business, which doesn't really apply now. These devices and our understanding now of them bares no resemblance to how we used them back then.

[DJ]

I worked for 6 years managing a design dept for an exhibition display company. We had 3 60" 6 colour piezo pigment printers to operate. They were 720 dpi printers. One of them was able to do 1440. Imagine that, 1440 dpi over 60 inches media width!

Ah, but you're talking DPI, which is dots, and the focus of this discussion has been PPI, which is pixels. Not the same thing.

We never saw any improvement in quality by having digital files at that same resolution.

I would have been very surprised if you did!

We did experience time delays from the huge file sizes though

60" @ 720 or 1440 PPI, eesh, that's gonna hurt

We always worked at half (360) and quarter (180) resolution.

Yep, is why I use 360, being a divisible of the native resolution it should hopefully minimise edge distortion in the interpolation.

Print quality was more affected by good scans - good tonal range, not over sharpened, good original trannie/print.

Agreed, makes a big difference, if your source material isn't up to scratch you're never going to see any difference, it's why I find scanning so frustrating, trying to get a decent enough scan isn't easy.

[Rob Lycett]

Hi DJ
I have to admit to only reading the last post by Joanna, and agreeing with the diminishing returns on higher resolution scans.

I can only say that I wish some of my past customers had thought about their files half as much as folk on the forum.

Rob

[DJ]

agreeing with the diminishing returns on higher resolution scans

It's true, the visible differences are very subtle, and to be fair, you have to look much closer than viewing distance to see them. Whether or not you consider them worth the effort, or indeed if you even like them, is a very subjective matter.

Perception of "sharpness" is also pretty subjective. I have beside me two A2 prints done the same as Joanna's test, one sent at 720ppi and the other at 240ppi, both printed @ 1440dpi. I can see the 720 one has more "real" detail, but the 240 one is perceived as ever so slightly sharper. I know it's an optical illusion caused by the sharpening ( just edge contrast ), but it's there nonetheless, sharpness is in many ways perceived.

For me, I like to know what each stage of the process is doing so I can choose based on the information, firstly so I might change stuff around to see where improvements might be achievable, and second because I find it interesting and like tinkering.

As I said, a big part of it for me is having to scan the trannie only once, high res, and just use that, scanning is a frustrating chore for me, hence the "Scan once, print many" philosophy.

[Rob Lycett]

Agreed. Life's far too short to be cleaning glass and film - or messing in Photoshop with the clone tool. Yuk.