Optical Resolution vs. Print Quality When Scanning Art for Traditional Offset Printing

Question

I'm new to this side of things - a writer who's venturing into self publishing. My illustrator, also a newbie, will be providing me the original artwork, but I need to figure out how best to achieve a professional output for traditional printing.

My illustrator is producing watercolor art on fine grain cold press watercolor paper. She's using 18x24 paper, though the illustrations are only 17.25 x 11.25 (which is an 8.5 x 11 children's book, inclusive of the bleed).

My question relates to scanning the illustrations for layout in InDesign. While I need this to be as cost effective as possible, I do not want to sacrifice quality. The end product must look professionally printed - crisp, clear, etc.

Through my research, it seems that 300 DPI is the standard recommendation for 4-color, offset print-ready files; and 300 PPI scanned at 100% scale equates to 300 DPI.

So here's my confusion. I'm looking at an Epson flatbed scanner that would so nearly accommodate the size of the illustrations that I think I can make it work without multiple scans (it accommodates 17.2 x 12.2), BUT the scanner has a maximum optical DPI resolution of 2400 x 4800. Am I correct in thinking the math works like this:

11.25" (height of illustration) x 300 DPI = 3375 17.25" (width of illustration) x 300 DPI = 5175

Which equates to 3375 x 5175 needed resolution which exceeds the 2400 x 4800 maximum optical resolution of the scanner? Or said differently, this scanner is only capable of scanning an image of my size at a little more than 200 DPI instead of the needed 300 DPI, and therefore the print quality will be subpar?

I may be completely confused and I hope I am, because this scanner appears to be the best available at the $3k price range which already pushes the boundary of my budget. Beyond that, things jump to $6k and more.

The scanner I'm looking at is the Epson Expression 12000XL Graphic Arts Scanner. Given my described circumstances, would anyone be able to:

• Tell me if my concern is valid regarding the Epson scanner, or correct me if I'm mistaken in my understanding and it should get the job done well for my purpose.
• Make a recommendation for a different scanner or alternative method for obtaining the quality I need for traditional, offset printing. I know there are services which will scan large-format art for a fee ($70 per illustration seems to be the going rate); but that would ultimately cost the same as buying the scanner, and having it would pay off with the next book if it can produce the needed quality.

Sorry for the long question, but huge appreciation for anyone's help!!

Thank you!

Answer 1

I like a lot the way you prepared your question. Congratulations.

1) You are confusing things.

Your scanner can scan at 2400 ppi (forget the 4800 for now), this is 8 times more than the theoretical 300ppi you need, and it would be used to scan, for example, a postal stamp at a high resolution to make it bigger.

2) Forget for the moment your unit conversions "300 PPI scanned at 100% scale equates to 300 DPI" Let us use just PPI. DPI is a unit used on printers, but let us use it for now interchangeably.

3) I understand that the illustrator is making the images almost at real size (in this case scanning at 300 ppi is ok). For archive purposes, and to leave some room to the design to accommodate images, and play with the design, I recommend that you scan them at 600 ppi.

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4) I am not sure if a scanner is the best option to scan a watercolor in a very texturized paper.

The light is shooted at a very specific angle and could or could not be the best lighting to enhance the texture of the paper.

Do you want the texture? Do you want to flatten the texture to show only the color? Do you want to show more texture?

Probably a better approach would be taking a photograph. With that budget you can afford a good quality camera, lens and illumination.