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Digital Printing: How Do Megapixels, Resolution and Pixel Dimensions Relate to Print Size?

Digital Printing: How Do Megapixels, Resolution and Pixel Dimensions Relate to Print Size?

“I have a 3264x2448 pixel image – what’s the best print size I can get from this image?”

“I want to print my image 16x20 – what’s my resolution at this size?”

“I have an 8 megapixel camera - how big can I print?”

If you find yourself asking any of these questions fear not, we get A LOT of questions like this, so this is the blog for you!

The most difficult aspect of all these concepts is understanding the relationship between what is captured digitally, and what you end up with in print, and this usually where the confusion lies. Hopefully by the end of this article you can better understand how images work and how megapixels, resolution, pixel dimensions, and size are all related to each other - then you can get the best results from our fine art and professional photo printing services.

A cat sitting in the sunlightA cat sitting in the sunlight

First let’s look at some basic information about this image.

Basic image information in PhotoshopBasic image information in Photoshop

Using Photoshop, the dialog box above shows the Image Size of the photo to its left. For reference purposes, this photo was taken with an iPhone 5s which shoots at 8 megapixels, and has a JPG physical file size of 1.5mb.

Starting at the top, the information tells us the Pixel Dimensions of the image. In this case, the camera used took the photo at 3264 pixels wide by 2448 pixels high. The Document Size is found below that. Currently it’s set at 25” x 18.75” which gives an image resolution of 130 pixels per inch. Notice the chain link beside those three items. This is important because the height and width the image, and resolution are all related. As resolution goes up the print size (width and height) will go down and vise versa – as the resolution goes down, the print size will go up. The reason for this is because a digital image has no absolute size or resolution – it’s all based on the pixel dimensions it was originally taken at. This is why it is ALWAYS suggested to set your camera settings to take the largest pixel dimensions it can at the highest quality it can. This way you will always be getting the maximum quality out of your camera at all times and giving you the maximum pixel dimensions it can.

It’s always easier to size things down after a photo is taken than try to ‘create’ pixels from nothing afterwards in editing.

Now you don’t need Photoshop to figure out all these sizes, like in the example above. You can also look at the image file properties and use some simple math to get the same results.

Image file properties Image file properties

Width: 3264 pixels
Height: 2448 pixels

Width (in pixels) ÷ Width (in inches you want it to be) = Resolution (of the image at this size in ppi)

So using width…
3264 pixels ÷ 25 inches = 130.56 resolution -- @ 25” wide the image will be 130 ppi resolution

Now that you have the resolution you can determine your remaining side…

Height (in pixels) ÷ Resolution = Height (in inches)
2448 pixels ÷ 130.56 resolution = 18.75 inches

Now that the math lesson is over, let’s move back to resolution, and talk a bit more about it, in regards to how much you need. The answer to this mostly depends on how your image will appear or what it will be printed on. For example images online or on a website typically need about 72 ppi. In short, this is because most images online are shown at a relatively small size, so the smaller resolution keeps physical file size down, which makes things load faster . Printed images on the other hand need a lot more resolution than that, seeing they are usually printed much larger than they are viewed on a screen. Now that we are talking about digital vs. physical media, let’s make a quick note just so we are clear, as this directly relates to what we are discussing:

PPI = Pixels Per Inch
DPI = Dot Per Inch.

While nowadays these 2 terms seem somewhat interchangeable, the correct times when to use each should be known. PPI is used to measure monitors, digital cameras, scanners and other medium where the image itself is still in a digital form. DPI is used to measure the physical medium once it’s out of digital form – so in this case printers would use DPI. Now back to resolution. While we could go further into the ‘best resolution’ to print at, which requires more math, and quite frankly more debate as it references the max dpi of the printer, how many color cartridges it uses, and what type of paper and or printing settings it’s on, for this discussion we will keep it simple. At American Frame we recommend that your image have a minimum of 130 ppi at print size, however, upon request, we will print lower resolution images. We have no ‘max’ resolution to print at just a max physical file size of 100mb. This is basically to ensure that we can service the broadest range of customers needs. So if you desire you images to be 360ppi at print size and they are sized that way, as long as the file is below 100mb it will be printed at that resolution. Here is a chart to give you a rough estimate of how big you can print depending on the Mega Pixel of your camera. We recommend your image stay within the “better” to “superb” range as shown below:

A print size versus camera resolution chartA print size versus camera resolution chart

More information like the chart above can be found here.

Now what happens if your image is too small? Well there are a few possibilities to fixing this. We can go ahead and print it at a lower than recommend resolution which could result in what’s called pixilation or artifacting being more apparent. What do we mean by this? Well let’s look at our cat image again:

Pixelation in the cat imagePixelation in the cat image

Pixilation happens when you blow up an image so large you can see the individual pixels that make up the image. When you are zoomed way out the image looks smooth, but when you zoom into a small selection your eye can distinguish individual pixels and jagged edges. Our example image has a maximum print size of 25”x18.5” at 130 ppi to stay above the minimum recommended resolution for American Frame.

Now if we wanted to print this larger, for example, at 40”x30” our resolution would drop down to 81.6 ppi and up close we would start to see those jagged edges like the ones above. How much of this will be visible would depend on the image and the quality/clarity it started at.

This is why we recommend our Resolution Proofs. This would give you an 8x10” section of your image printed at full size, which then once you receive your proof, you could determine yourself if the pixilaization is apparent or not. If you decide it’s too jagged for your liking you can either choose to print smaller, or if you have access to image editing software, you could choose to up-res your image.

Up-Ressing or Ressing Up is basically a software fix to create or add extra resolution to a digital image that isn’t already there.

Original close-up of the cat's whiskers next to the up-ressed versionOriginal close-up of the cat's whiskers next to the up-ressed version

It should be used with caution as basically the program is creating these pixels from nothing and adding them into your image. Essentially the effect tends to blur the image overall more so than if it was printed normally. The reason for this is that a larger print is usually viewed from a greater distance than the distance viewed of a smaller print, so the effect that it has, is masked because you are standing back and away from it.

So in conclusion, remember that a digital image has no absolute size or resolution – it’s all based on the pixel dimensions it was originally taken at. The more pixels you have the more clarity you will have, as your resolution will be higher and give you more size options possible to print at. So, always set your camera to the largest pixel dimensions available and at the finest quality it can take. It’s always easier to start with something big and go smaller than the other way around.

Want to learn more? See our other printing articles:

Fine Art Printing Technology- Giclee to Archival Inkjet Printing
How to Order Custom Digital Printing and Framing at AmericanFrame.com
Choosing the Right Paper for Your Project- Part 1
Choosing the Right Paper for Your Project- Part 2
Choosing a Print Size and Determining Framing Prices: Two Easy Methods
How Do I Order a Print Only at AmericanFrame.com?
What Is the Largest File Size I Can Send You for Art Printing
Do You Stretch Large Canvas?
Clean, Crisp and Contemporary: Get the Look with Art Printed on Acrylic Plexiglas
How to Set Up Print to Canvas Gallery Wraps with Mirrored or Colored Borders
The Vocabulary of Giclee- Digital Printing Technology

May 1, 2014
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