Image Resolution, PPI & DPI

WHAT IS IMAGE RESOLUTION, PPI & DPI?

This content was written by ChromaZone Ink, Melbourne FL.

Understanding Image Resolution & the Pixel Problem:

Understanding image resolution, ppi & dpi are key to having your visual project turn out the way you expect it to.  Doesn’t it suck when you take an awesome picture, then have it printed as a special memory and it turns out fuzzy and pixelated?  You bet it does!  –  By “pixelated” we mean the edges of your images are jagged or you actually see the image made up of little squares of color, the smallest element in digital imagery.  There are 4 basic concepts to understand about image resolution.

Problem Solved!

By simply understanding the 4 concepts described below, you’ll become a better photographer and have fewer disappointments when you send your creations to be printed by professionals.

One of the requests we at ChromaZone Ink Canvas Printing Orlando often receive is “Can you print this picture from my iPhone in a large poster size for me?”  The answer to that is always – “It depends on the resolution and size of the original image – let’s take a look…”  Then, if the image is digitized we upload it to our site, open PhotoShop and check the size to reveal the answer. Contrary to popular belief, if the resolution of a digital image is not high enough to print it at the larger size, you can NOT just use computer software to increase the resolution to get good results.  The most important thing to remember in digital photography, is that you cannot print what was never there to begin with.  You can use “interpolation” tools to “fake” additional digital information, but that will never render the print quality that matches what taking the picture at high resolution to begin with, can render.  In order to explain why, there is some terminology you’ll need to understand first. We’re always happy to explain this with a phone call too: 321-312-4800 | 800-501-2901.

1. The Pixel:

A pixel is a unit of measurement for digital images as well as a unit of measurement for the computer and TV screens that display the digital images. A pixel is the smallest element that a photo on a screen can be divided into. You cannot see a pixel with naked eye without zooming into it using software. A pixel is generally measured in a number per square inch, giving rise to the acronym “PPI” or “Pixels per inch.  Here is a link to a great video where “Dayj” does a great job at explaining pixels in depth, and in less than 3 minutes:

 

Canvas Printing Orlando - Image resolution, ppi & dpi?

 

…but the main concept to understand is that the more pixels you can cram into one square inch of your photo, the better it is going to look, hence the term “Megapixel” which is equivalent to 1 million pixels.  So a camera with higher megapixel capability is going to be able to render bigger and sharper images.

2. PPI vs. DPI:

PPI or “Pixels Per Inch” is often confused with “DPI” which means “Dots Per Inch.” DPI is a similar concept to PPI but refers to output that is NOT on a computer screen, but is PRINTED, such as on posters, business cards, magazines etc. Remember that “PPI” refers to image output on TV or computer/device screens. The two terms are often used interchangeably, but in reality they do not mean the same thing.  Much like digital quality, printed quality is determined by how many dots of ink there are in one square inch, as opposed to how many pixels of information there are in one square inch of digital images on a screen.

3. Resolution:

Think of image resolution as the pixel density in screen images or dot density in printed images. If you have 100 pixels of image information in one square inch, that is far less dense than if you have 2500 pixels of image information in that same square inch.  Therefore, the resolution is much higher / better in the digital image that has 2500 pixels of image information versus the image that has only 100 pixels of image information. The higher the resolution is for an image, the better it will look when printed because there is more detailed digital information that printers can output.

When we talk about image resolution, we also have to talk about screen resolution.  Screen resolution is not dense at all compared to image resolution.  At the time of this writing, a typical 23” diagonal (non-retina display) computer screen is often 1920 pixels wide by 1080 pixels high. Screens have a set number of pixels per square inch, and that never changes unless you get a new monitor.  This is why low resolution images usually look pretty good on computer screens – which can be deceiving because they will not look that good when printed. To get into the “nuts and bolts” of image size versus resolution and how it is calculated, we recommend you read the article entitled: “Image Size and Resolution Explained for Print and Onscreen” by Helen Bradley.  You can get the URL from our sources listed at the end of this article.

4. Interpolation: 

A method of constructing new (or missing) data by sampling surrounding data and estimating what the new data should be.  All too often we here at ChromaZone Ink Canvas Printing Orlando have clients that come in and tell us that they had a small image (for example 4” x 6” at 300 ppi resolution), but they used PhotoShop or some other image manipulation software to make the image 16” x 20.”  When people do this, the software is actually using the software’s “interpolation” tool to create the additional pixels of information, by sampling the colors of the surrounding pixels, and “guessing” what color the new pixels should be.  Sometimes interpolation can do a pretty decent job, but more often than not, it creates a blurred interpretation of what the actual image was supposed to look like.  Increasing the image size does NOT increase the pixel density.  It actually lowers the pixel density (remember once a picture is taken it has a set number of pixels!)  Think of pizza dough.  You’ve got a quarter pound of pizza dough to make a 16” pizza.  But you’ve been told to use that same quarter pound of pizza dough to make a 24” pizza.  What happens to the dough when you stretch it that thin???  Right, it gets holes in it, doesn’t it?  Same thing happens to digital images when you try to stretch them.  The only difference is that the software’s “interpolation” tool throws a little extra flour into those holes, hoping to patch the dough in some way, but there are no eggs or water to hold it all together.  Again we need to stress: increasing an image’s size does NOT increase the pixel density (resolution).

What Does All This Mean?

So what does all this mean when you have some fantastic shots on your smartphone and you want to have them printed in large sizes?  Well, thankfully, most smartphone built-in cameras always shoot in full resolution which is usually good enough to get pretty large images.  The problem comes when you upload the image to Facebook or any photo album Internet site, because many of them automatically optimize (reduce the file size/resolution) of images for faster loading and viewing.  Facebook is the worst for this!  Another problem is a screen shot— taking a picture with your smart phone’s camera is good, but taking a SCREEN SHOT creates a very low resolution image and is rarely good enough quality for large format printing.  One final issue we see is when you try to email an image to us from your smart phone if you use anything but the actual size image.  For example, when you try to email a photo on an iPhone you will be presented with 4 options when you click the send button: Small, Medium, Large or Actual Size.  Actual size is the highest resolution, and the one you should select if you want to print the photo using ChromaZone Ink Canvas Printing Orlando or Melbourne.

The Easy Way

An easier way is to use the ChromaZone Ink Canvas Printing Orlando “GET AN IMAGE ASSESSMENT” upload button.  When you click this button on our home page, it will take you to our ftp site where you can upload large images quickly – much faster than email, and directly from your smartphone.  There is also a comment box where you can ask us a specific question. The image goes to our server and we will get an email alerting us to its arrival.  We will check the resolution and answer any question you enter in the comment box.  ChromaZone Ink Canvas Prints would love to be your giclée printing company, call us at 321-312-4800 | 800-501-2901.

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Sources:
Image Size & Resolution Explained for Print & Onscreen: https://digital-photography-school.com/image-size-and-resolution-explained-for-print-and-onscreen/
How Can I Change the iPhone Camera Resolution? https://sonru.zendesk.com/hc/en-gb/articles/206430499-How-can-I-change-the-iPhone-camera-resolution-
Changing the Megapixels on an iPhone: https://smallbusiness.chron.com/changing-megapixels-iphone-47183.html
Two Minute Design by “Dayj”: http://2-minutedesign.com

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