Why Published Images Will Look Different than Inkjet Prints. Part 2

A two-part post on preparing images for publication.

Publications use the geometric structure of halftone dots to interpret pixel values as tonal values on paper surfaces. Each pixel produces up to four overprinted color halftone dots. These halftones dots translate darker values of each color into large dots and lighter values into smaller dots. The full range of darkest-to-lightest tones produces dots that vary in size from occupy variable.

Color Halftone Dots

To avoid the visually annoying conflict that occurs when geometric grids collide (called a moire pattern), each CMYK grid pattern is set on a very carefully calculated angle. The positive edge that inkjet images have over halftone images is that the image resolution required for inkjet prints is much less than what is required by the halftone process employed by publication images, though that’s not the real surprise.

Dad Color HTEven more shocking is how much less resolution is required for either process than what is commonly perceived. The universally preached standard for printed images printed at 150lpi (lines per inch- the method used to measure printing dots) is 300dpi at final dimensions (a 4×5 inch image reportedly requires 1200 pixels horizontal and 1500 pixels vertical). This 300dpi image will produce a file that is 5.15M.

The physical science behind lithography (the Pythagorean theorem) has proven that this calculation is quite excessive. The actual resolution requirement for printed images is only 212dpi, which produces the identical quality reproduction but at half the file size (2.57M). This means that you can store twice as many files on your hard drive with no loss in quality. That’s a big deal!

inkjetvshalftoneThe same good news can be applied to the inkjet printing process though the image size required is even less than litho images. Common assumption (usually stated as dogma) is that images sent to inkjet printers should also be 300dpi at final dimensions. This assumption is also grossly overstated. Inkjet printer technology (even at 14.4K print resolution) requires only 150dpi to produce stellar results. This inkjet resolution will produce images weighing in at only 1.29M. That’s just 43% of the size. 

But the most important issues that must be addressed have to do with color fidelity and tonal reproduction. There is a huge difference between the way inkjet images and print publication images are reproduced, making a significant difference in the way the images appear when they come out the delivery end of the process.

Inkjet printers are like ballet dancers while printing presses are more like Sumo wrestlers. It’s chamber music vs Thunder clap. One is graceful and articulate, the other violent and powerful.

RGB Inkjet printerThe biggest difference can be seen in the control over highlight and shadow detail. Inkjet inks are sprayed onto substrates through a very controlled matrix of 14,400 dots per inch using a slow and measured inch-per-minute process. Publication presses smash ink into paper under extreme pressure, at speeds exceeding 10,000 rpm translating the entire tonal range into a limited matrix of just 150 variable-size dots per inch. Publication presses are huge, high-speed, rotary rubber stamps.

CMYK

You can dress a Hippopotamus in a tutu but you can’t expect it to pirouette. Something has to give, and in this case, it’s the entire reproduction curve. The shadow details want to close in, the highlights tend to disappear, and the middle tones bulge. While the printing industry has addressed many of these problems with their G7 process controls and plate curves, the beast is still a beast.

Next time you edit you photos, think of how distinct the detail was in the original scene. Let that be your guide. Don’t overproduce your images. Just determine to show your viewers what the original scene dynamics looked like.

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Think about it!

Please leave a comment.  If you find this worthwhile, please share it with your friends and sign up for more. This ain’t rocket science, but it is information that is many times overlooked (and sometimes overstated). Take some time to get back to the basics and your photographic results will give evidence that you did.

That’s the way I sees it. If you have an argument with this position, take it to a higher court! In the mean time, sign up (above right) to get personal notices of future posts. You can’t beat the price.

I enjoy speaking to schools, photo clubs and organizations every month presenting programs on digital photography, post production, and color science. If you’d like me to speak to your group, drop me a line.

If you’d like to understand even more of what makes color work, how light behaves, and how easy it is to shape the light in your photographic images, go to http://gottaknowvideos.com and get Bright About Light!

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About Herb Paynter

Herb is a published author, photographer, retoucher, color reproduction specialist and a regular writer for Digital Photography School. Download his iBook Digital Color Photography from the iTunes store and view his Light and Color video series at Gotta Know Videos.com.
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