The Prepress Perspective- Week 3

Posted on February 15, 2012

The Low Down on Low Res Images

You’ve checked your resolution in Photoshop, it’s at 300 pixels per inch- but Wentworth is still telling you your image is low res! What gives?

Resolution is probably one of the most confusing things about printing. I’ll see if I can simplify it a little for you. Let’s start from the beginning…

Some common things you may hear are PPI and DPI. PPI stands for pixels per inch. Google defines a pixel as “A minute area of illumination on a display screen, one of many from which an image is composed.” So, the more pixels you have, the more detailed and clear your image will be. This is your photo’s resolution. In a perfect world, every image would be 300 PPI, but we know that is not always possible. 300 is the magic number in printing, getting lower will start looking fuzzy and going higher won’t visually make a difference, but will make your file larger!

DPI stands for dots per inch. This relates to your printer. Printers (referring to the machines) print in lots and lots of little dots that make up one image. (Crazy right?) So the greater your DPI (the more dots you have) the more detailed your image will be. Make sense?

Let’s recap. PPI = computer screen, DPI = printer. Ok, now what about the lo-res images…

Let’s say you have a 300 PPI image, but the actual size of the image is 2 inches x 2 inches. If you make the actual size LARGER, your PPI will get SMALLER. PPI and actual image size are inversely proportionate. This is where a lot of folks get confused. InDesign has this really great way to tell what resolution your image is if you are needing to resize it. When you look at your links tab, make sure you have the “Link Info” open.

See where it says “Actual PPI” and then “Effective “PPI”? The actual PPI is 300, which is good, but the effective PPI at 249 means the image has been made a bit larger than it was at 300- making the image a slightly lower resolution. With this photo, it wasn’t a drastic change, so that 249 PPI is still going to look ok. If the photo were enlarged say by 100%, then there would be a low resolution issue.

This works both ways. See how on this one the actual PPI is 240, but the effective PPI is 453? This means that the original image size was made SMALLER so the resolution got LARGER.

So to make a long story short, if you enlarged your image from its original size, that is why you have a lo-res image in your project. I could sit here the rest of the week and talk more about image resolution, there is so much information, but hopefully this is enough to get you started!

See ya next week!



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