Posted on Jul 3, 2013 in Tech & internet
Why do the photos I save and print from the internet look so bad? The pictures come out with blotchy dots and blocks — nothing like they looked on my monitor. What am I doing wrong?
Bottom line: There’s not enough information being provided to the printer to make you a nice, crisp print.
The issue is one of dpi (dots per inch) and/or ppi (pixels per inch), also known as resolution. It’s the amount of data per inch.*
Put simply, in one square inch of what you see on the average computer monitor, there are 72 dots (called pixels) going across, and 72 dots down. Like in this little picture on the right — if you counted all those pixels, you’d find there were 5184 (72 x 72) individual little dots. This could be described as having a resolution of 72 dpi, and is illustrated above in the lantern on the left.
While we see generally see things perfectly clearly at about 72 dpi on the web, for printing, you need to have a lot more dots per inch — usually at least 300 — to make the picture come out properly. Otherwise, you’re just trying to stretch those same 72 pixels to fill the space where 300 belong… resulting in something that looks a lot like the picture of the lantern above on the right.
The 300 dpi and up guideline applies equally to having your photos printed or to having a magazine printed — you need enough image data to fill in all those gaps. (If you’re printing line art or graphics — like, for example, a comic book — you will want a higher dpi to ensure the blacks come out as dark as they should be.)
So when you are considering printing an image that you see on your computer, envision it shrinking to about 1/4 of the size when you print it out. By the same token, if you want a 4×6 photograph to come out nicely on a home printer or through a photo printing company, that original image file should be a minimum of 1200 x 1800 pixels.
* A note on dpi vs ppi: Generally, web resolution is measured in ppi, because there is not a fixed pixel size — depends on the program, the monitor, etc — while dpi is the standard for printing. Here is a more detailed explanation of the difference, which is not really necessary to fix this photo printing problem, but will hopefully shush a few snarky types.
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