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Have you ever wondered why some images appear sharp in one format but then they’re blurry or lack definition when viewed on a different screen or printed out? This is all to do with DPI, PPI and resolution and, despite a general rule of thumb of images being 72dpi for online and 300dpi for print, there is no true magic bullet.
Dots or Pixels?
There can be lots of confusion about the acronyms DPI and PPI. This confusion is understandable, given that people often use the terms interchangeably. So what do DPI and PPI mean, and how do they apply to printed photographs and digital image files?
What is DPI?
DPI stands for dots per inch and refers to the resolution of a printer. It describes the density of ink dots placed on a sheet of paper (or any other photographic medium) by a printer to create a physical print. DPI has nothing to do with anything displayed digitally and this is where a lot of the confusion can occur.
What is PPI?
PPI stands for pixels per inch. PPI describes the resolution of a digital image, not a print. PPI is used to resize images in preparation for printing. To understand this, we also need to understand what a pixel is.
A pixel is the smallest building block used to create an image on a screen. Pixels are square and arranged on a grid. Each square is a different colour or hue. Because pixels are so small, our eyes can’t detect the individual elements on the grid and our brain blends each pixel into a smooth digital picture.
Digital Image Size
It’s also essential that we understand what digital image size means. The size of a digital photo is created in your camera. It depends on the model of camera you’re using and how you’ve set up your camera. For example, if a camera captures a raw JPEG file that is 6,000 pixels wide by 4,000 pixels high, you’d have three different image size choices: large (6,000 × 4,000 pixels), medium (4,240 × 2,832 pixels) and small (3,008 × 2,000 pixels).
If you reverse engineer the math, 6,000 × 4,000 = 24,000,000 pixels, or 24 MP (million pixels or megapixels). When you hear someone say they have a 24 MP camera, this is what they are referring to.
PPI and Screen Resolution
PPI can also be used to describe screen resolution (not to be confused with digital image resolution). The resolution for any particular screen is a fixed quantity. Screen resolutions vary between devices and are continually getting better. Displays with higher resolutions have device pixels that are smaller and more closely packed together. Images on higher resolution screens appear sharper and crisper than the same images displayed on lower resolution devices.
Since the pixel count is fixed for any device, image resolution will not impact how a photo looks on that device. You can export an image at 72 PPI, 96 PPI, or even 5,000 PPI, but for a given device, you won’t see any difference in how the picture looks. It is the picture size – the physical number of pixels along the length and width – that changes how the image looks on a particular display screen, not the image resolution.
Why Does It Matter?
It’s not just about clarity and looking amazing. Thanks to the way Google ranks websites, variables such as how quickly your images load can also have an impact on your Google position. When we talk about “optimizing” images for the web, you can think about this in the following three ways
Making images that:
1) Look good.
2) Load quickly.
3) Are easy for search engines to index.
With web images, you want to find the right balance between size and resolution. The higher your resolution, the larger the file size will be. In the world of print, high resolution images are a good thing. But on the web, large size, high resolution images can slow down your website’s page speed. This really impacts your users’ experience and, potentially, your search engine ranking.
If you’re unsure of how your website is working with your images, you can check it out here: https://gtmetrix.com/. If your PageSpeed Score is low take a look at the sections that reference images and see if you can make some quick changes to help improve your load speed.
Planning what you need.
Whether you are looking at headshots, personal branding, event photography or product photography, make sure you plan out exactly where you want to use the images. This will help guide you in making sure you have correctly-sized images which give great quality without compromising on load speed.
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