Quality halftone image reproduction is central to the print process. I’ll set aside vector art for the moment, as those are generated under a different protocol. And yes, numbers help, but they don’t tell the whole story.
Digitally-created images are unlikely to ever see the bright light of a scanner. But they are bound by the same rules as scanned files.
Scans are made from either flat art, or negatives and chromes. Flat art is scanned on flatbed scanners of varying horsepower, or drum-scanners. Film files can be scanned on a variety of scanners ranging from insanely excellent down to consumer-borderline competent. All scanners have their own proprietary anomalies.
For the purposes of higher-end print production, placed image is typically 350dpi at 100% in the layout. This is true across the board: Photoshop, Quark, InDesign and Adobe Illustrator.
(Note: In Quark and InDesign it is far easier to verify an image’s enlargement/resolution ratio than in Illustrator, where you have to dig. Read why Illustrator is unqualified as a page-layout application).
Scenario 1: High and Low
If you import an image which is 350dpi at its native 100% into a page layout scenario like Quark or InDesign at 100%, the ratio is 1:1, and everything is golden. However, if I import the same file and then enlarge it 125%, the image inversely decreases to 280 lpi.
350 / 1.25 = 280dpi
When I’ve encountered this numeric, I’ll flag it as a potential problem. When I’ve called advertisers about this problem, reactions vary, ranging from “uh-oh” to “it worked when I sent this identical file to Rolling Stone/NY Times Sunday Magazine” etc. This is when I tell them that the difference between art-book publishing and web-offset periodical printing is considerable. Images go soft, banding starts to appear, and image degradation becomes more evident. Oh.
However I’ve seen rare scenarios where images fell short numerically, and were saved by accidental or intentional bold contrasts, even halftones, and overall image quality as evidenced by the customer’s target proofs. The layout was given a pass and off it went to be wet-proofed.
But that is the exception. Like the drunk driver going over a canyon rail and walking away from the wreck.
The opposite doesn’t play out the same way. I’ve seen layouts where the original image is 350dpi, but is imported into a layout at 125%, equalling 437.5dpi.
350 x 1.25 = 437.5dpi
This is excessive, as current printing typically doesn’t require this.
On the higher end of grotesque, I’ve looked at layouts where a placed image is 15% of original, and the customer’s target proofs are 13×19. And printed out on warm toothy art paper, which typically will add 5% yellow and warm things up quite nicely. Which is fine—until the wet-proofs come back.
- Under-resolution images need to be replaced by higher quality files
- Over-rez files get reduced in either pixel dimensions (Quark) or percentage of import (InDesign)
My G5 Is A Beast, Why Bother?
An eternal production question. Because the monstrous spool file you are generating every time you print files that are massive is costing you time and money. Every additional calculation you make with an image (rotation, skew, horizontal/vertical flips) is an additional burden on the document and a clear sign to the pre-press guy or gal that You Are Ignorant.
Scenario 2: Real and Junk Pixels
For example: I open a customer file which is an 8-1/2 x 11″ page document that has the following image in it, complete with bleed. The placed image bleeds 4 sides in the layout.
Its starting to look like a good day. The file’s native dimensions are identical to the layout requirements.
Now look at the Image Size palette for this document:
Numerically the file is good to go.
So what happens when you get a file that numerically checks out, but just looks plain weird?
Imagine an 11 x 17 spread, and an extreme closeup of a young toddler. The child’s face looked like it had been put through a Photoshop Mosaic Tile filter. This is what the previous image would look like if it had been treated the same way;
My first reaction was “Yipes!”
- a stylistic statement (I’d been to a lot of galleries lately)
- an inadvertent mistake by a designer (ie, low-rez jpeg not swapped out)
- a basic technical error.
The advertiser was contacted. We found out that the designer had put the original 2 x 2-1/4″ neg on a mid-level flatbed transparency scanner, and then enlarged it to fill the space available.
The pixel dimensions are identical, but the outcome is considerably different. Seems pretty obvious, but this is a continual travelling partner in the World of Pre-Press.
The Advertiser resent their file with a high-resolution scan and the results were considerably improved.
Image management is a combination of metrics and alchemy. The guidelines I’ve mentioned will go a long way in getting an image to print to the best of its original capacity. It has nothing to do with aesthetics—I’ve looked at many files containing images with proper numerics and zero content. The alert designer, pre-press operator, and whoever else that comes into contact with the file are all obliged to do their homework and make sure nothing falls between the cracks.