How to find the print size?

File size Vs print size?

This is a question that we are asked frequently. As always there is a ton of technical information available, which I don’t have space to cover here.  I will give you some basic guidelines, such as defining file size and how to decide if a file is big enough to meet your client’s print requirements.

First we should know the pixel dimensions of our cameras. By using this information, you can calculate the file size that your camera can create. Here’s a good website for calculation.

Now I know my file size, how can I figure out the optimal print size?

As a rule of thumb, for the best photo quality, you should create your final work with 300 dpi as the output resolution when using wet printers (those in commercial photofinishing labs). Inkjet, pigment, and dye-sub printers can print a very high quality image using only 120 dpi. So, let’s put this information to work:

Here is the pixel count of a 12 MP camera in large setting: 4256 x 2832.  This is the native resolution for this camera. If you want to know how big a photo lab printer can enlarge your image, simply divide each number by 300 to find out the size.

4256/300=14.19

2832/300=9.4

So 14×9.5 inches is the optimum size for great photo quality from a wet lab.

Unlike monitors, typical high quality print resolutions range from 180 dpi on the low end to 360 dpi for professional quality results. Another big difference is that these print resolutions aren’t fixed in the printer the way they are in a monitor. You can take the same file and send it to the printer at any resolution setting you choose. Basically when you do this you’re telling the printer how far apart to place the individual pixels on the printed page. Place them too far apart and your image will take on a blocky, digitized look. Place them unnecessarily close, like 720 dpi, and you’ll be limited to a very small print with no added quality. Remember that resolution tag that was ignored for web use? Well it’s exactly what we need to control printing resolution for hard copy output, so we can’t ignore it any longer. Unlike your web browser, your printing program looks at the resolution tag and uses the value you enter there to control the printer itself.

A word about printer resolutions

When we buy photo quality printers, we see advertised resolutions like 1440 dpi and not the measly 300 dpi described above. Colour printers create their wide range of photo quality colours by placing tiny droplets of different ink colours down, to create all the combinations of colour and brightness. A big number, like 1440 dpi, is a good thing in a high quality printer, but it’s not the resolution you care about when sending a file to the printer.  There are a lot of terminology debates raging in the photo world such as: dpi vs. ppi vs. other ways to describe resolution.  I use the term dpi (dots per inch) to describe actual droplets of ink like the 2880×1440 micro droplets of ink placed on the page by my Epson printer or in the places where it’s just historical convention like 72 dpi.  I use the term ppi (pixels per inch) to describe the much larger pixels displayed on a screen or sent to the printer.  Others use these terms differently.  Just remember that a pixel is the smallest piece of colour and tone information in a digital image and a photo quality printer uses a whole bunch of tiny droplets of ink to synthesize each pixel on the printed page.

Using print resolution to control print sizes

So now you’ve got some control on sizing your prints by adjusting the resolution setting. But what are the tradeoffs? Let’s start with our earlier example of a 12 MP camera’s native file at 4256 x 2832 pixels, printed at 300 dpi gives us a quality print of 14.2” x 9.4”.  Print it at 240 dpi and the same file gives you a 17.8”x11.8” print and at 180 dpi you’ll get a whopping 23.6”x15.7” print. All from the same native file, without any image resizing. Of course, there’s no free lunch: as you print at lower resolutions you’ll eventually reach the point where the individual pixels are spread too far apart on the page and your image will suffer.

How far can you push the resolution to get big prints?

Well that’s up to you and depends on your printer, the paper and inks you use, and your own quality standards. There’s no absolute here, but many folks consider 300 dpi the gold standard for high quality output on modern ink jet/wet photo printers. It’s such a common high quality setting, that it has earned the name high res and is a standard image resolution in the publishing industry.

For other types of printers, please check the menu of your printer.

These websites offer more useful information.

Mega Pixel Chart

This ONE  is very informative.

This one has some visual Samples.

And, last but not the least, is this ONE and I recommend everyone reads this article. It has a good explanation about different formats as well.

Now there’s another good reason to shoot RAW!

Do you want to know more about how these variables affect our editing capability and prints?

Visit our Workshop page and Sign up for our Photoshop and Lightroom workshops.  Class size is limited! Please book your spot soon!

That’s all for now.  As always, we appreciate your comments.  Please send comments, questions and suggestions.

Do you have suggestions for future tutorials? Please send your suggestions and comments to: info@omnilargess.com

Stay tuned for more tips on photo editing.

Ted and the Omnilargess team