image quality

note: this page has no association with the US Army or Borden Institute.

I make medical textbooks for a living. That is, I get sent words and pictures and I make them into something that looks like a book. My old English teachers would be horrified to learn I have anything do to with a field where I might be responsible for deciding where commas go. Let me assure them, most of the time I don't even read the text.

A lot of the pictures are of dubious quality. I'm making this post in the hopes of explaining what I'm looking for in image quality.

Over the last several years the quality of the images I get to work with has diminished. With the rise of digital cameras most people have traded their old film cameras for a reasonably priced digital equivalent. Or worse yet, their phone. Actual photographs could be scanned in at a high resolution and made just about any size you like. A pricier digital camera, like mine, can get me a picture that can be printed at 300 dpi across a standard piece of letter sized paper. But most people don't buy their cameras with the intent of using them to retake scenes in small, damaged, or corrupt picture and then publish them. Most people want a more modestly priced camera that will allow them to post pictures on Facebook or send through e-mail. Usually, those pictures can't be expected to fill even one of the two columns we use on a page of our books. Not at 300 dpi, anyway.

Dpi stands for "dots per inch". A computer monitor shows 72 dpi [huge disclaimer removed]. In print we like 300 dpi. More than that is a waste. Less starts to become grainy or blocky. And it gets the people at the Government Printing Office to grumble at us.

It's hard to show the difference in quality between print and screen resolution when we're looking at the example on screen. It's like showing commercials for HDTVs on older televisions. You can't see the difference on the lesser medium. So I want you to follow this link. It'll take you to a PDF stored in Google Docs. Page one shows a 300 dpi picture and a 72 dpi picture. You can see a difference between the two if you look, but Google Docs does degrade them a bit. If you go to File and Download Original you can see the non-degraded version on your computer. At first the 72 dpi picture just seems a bit more hazy. Then you'll start to look at the edges of thing. Where the flower petals meet the grass or concrete the line is a bit jagged. Compare the yellow petals. Have a look at the edges of the purple leaves in the corner. Zoom in just a bit and the problem becomes more much more evident.

And you can't make a 72dpi picture into a 300dpi picture simply by changing it in Photoshop. At least not without reducing the size of the picture to 1/4 of what it was. Instead what you get is a high quality print of a low quality picture.

Page two of the PDF shows the same thing you see below.
Both pictures are jpegs. One is saved at the best quality. The other at the worst quality. At least according to Photoshop.

high quality jpeg - 72dpi - 434kb

low quality jpeg - 72dpi - 172kb

See what happened to the pebbles in the sidewalk? How the red flowers get misshapen? Or the yellow petals start to resemble a flock of deformed butterflies?

Jpegs were created to make images smaller for transfer by floppy disk or modem. It's why they, along with gifs, were chosen to be the default image types acceptable on the internet. But in converting them to jpegs some data is lost. The picture, as you see above, degrades.

We now have CDs, DVDs, DSL, and Gmail accounts with 20mb attachments. The file size is less important. Some editors still save their images as low or medium quality jpeg to make the files smaller. Please don't. We have the storage. We have the speed. We WANT the huge files. Better to have the data to burn rather than have to return the image as unusable.