Thread Count of an Image File

You’ve been working on your organization’s Annual Report for MONTHS and your job is just about done: the copy has been signed off by the board, the images have been chosen, data has been gathered for graphs and charts – you are ready to pass all the files on to the graphic designer. What a relief to have it off your desk and out of your head for a little while so you can concentrate on the myriad of other projects on your plate.

Just as you’re settling into writing next year’s marketing plan the phone rings. It’s the designer. “Hi, the images you sent are 72 dpi at 100%. Do you have higher resolution images? And do you have a vector file of your logo?”

Photo by ohhhbetty, flickr

Huh? Can you translate that please?

1. What are dots per inch (dpi)?
When shopping for sheets you’ve probably noticed that the higher the thread count the higher the price. High thread count fabric is denser and feels silkier. It’s the same with digital pictures except instead of thread count we are looking at dots – dots per inch (dpi), specifically – the more dots per inch, the higher the quality of the image.

2. What do you mean by 100%?
Simply, 100% is equal to the size you’d like the image printed. To print an image at 5 x 7 inches we need a file that is  300 dpi at 5 x 7 inches  (or 150 dpi at 10 x 14 inches; or 72 dpi at 20 x 28 inches).  Why 300? because that’s how a press works. (Something to be covered in a future blog post.) To look nice on a computer monitor, however, images need only be 72 dpi at 100%. Want to grab your 5 x 7 inch image from your website? That’ll be fine if you want to print it at a 3rd of the size you see it on the site. If you want it bigger, it will pixelate.

Pixelate?

Going back to the sheet: let’s say you decide to buy a beautiful floral twin (top) sheet at 300 thread count. When you get home, your bed has magically turned into a king size! Fabulous! But you still have this twin sheet that you want to use. So you go ahead and spread it over the mattress. It doesn’t fit. Someone suggests you try stretching it. So you get four friends together and you all take a side and pull. It stretches! As you pull harder and harder small openings between the threads appear – you can see mattress through the fabric which is getting thinner and flimsier, the floral pattern is  becoming blotches of color. By the time it “fits” the king-size bed it is down to 72 thread count and is so flimsy and abstract as to be rendered useless.

The same is true for images – stretching a low dpi image to fit a large space reduces it to visual mush.

3. Higher resolution?
Resolution equals dpi. The higher the dpi the higher the resolution. As mentioned, for print, images need to be 300 dpi at 100%. For web, they need only be 72 dpi (which is why you can’t print with images grabbed from your website.)

4. What’s a vector file?
A vector file is most commonly created in Adobe Illustrator and has .ai or .eps at the end. Instead of dots (like .jpg and .tif files) it is  made up of points and lines filled with solid or gradient color that the computer understands mathematically. The image can be altered by moving the points and changing the fill color(s). This means that the computer can be told to move the points proportionately and equally, hence, enlarging the image.

Imagine a bottom sheet – it has elastic all around the perimeter. The elastic stretches to fit around the mattress and the fabric fills in the space between without distorting or puckering. The difference is that, unlike the sheet,  vector images have no limit to how big (or small) a space they can accomodate.

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The best time to keep these rules in mind is when you are first gathering elements to be used in the printed piece. If you have any doubt about an image or file ask your designer. She will be happy to work with you on finding the best image files for your document; after all, the piece is as much a reflection of her design skills as it is of your organization. And we all like to sleep in nice sheets.