Image Optimization

Image Optimization! JPG, PNG, PDF, EPS, GIF, AI, SVG, PSD oh my…

There are so many image file types but what is the difference and which one should I use???

Image optimization is a vast topic, but this post will give you a basic understanding and overview of image and graphic file types, formats, and extensions. And more importantly, how to use and optimize your images — whether you’re a graphic/web designer or if you’re just attaching images to an email or sending a logo file or design to a printer. It may not be a sexy topic, but it’s important that you are using the correct ones on your website and that your images are optimized!

First off, there are a lot of file types out there. Some are formatted for documents, spreadsheets, and text programs; others are formatted for code, computer systems, etc. but in this post, I’ll focus on graphic and image-related file types that we all knowingly (or unknowingly) use on a daily basis.

To put it simply – graphic & image files are either one of two file types:

1. WEB (Bitmap or “Raster” files)
2. PRINT (Vector files)

All file types, whether JPG, PNG, PDF, EPS, etc will be either a web or print file and there’s a big difference between the two. We’re going to cover web files vs print files and I’ll briefly explain the most popular extensions within each file type. We’ll also expand on the most important aspects of each type including color space, resolution, and size which we’ll go into more detail below.

In short, Web Files are bitmap files (also known as “raster”) that are built within a certain set of pixels. These look great until scaled or expanded as they pixelate and blur as the image below shows.

Print Files are known as “vector” files which can be expanded and scaled up without losing quality. Vector designs are built within mathematical lines instead of pixels so they remain sharp as shown below and aren’t confined to a certain width or height like web files.

Ever had a picture or design that looked great on the web but looked terrible when it was blown up or printed? That’s exactly what happened. Important to know is that some programs like Adobe Photoshop and many image editing/web editing software are “bitmap” or “raster” programs while Adobe Illustrator, In Design and some text editing software are “vector” based programs.

So with that said…let’s have some “fun” and get into web vs print files.

1) Web Files

Small, optimized for web and fast loading but are set to certain size and will pixelate if scaled.

File Type: Bitmap (or Raster)
Color Space: RGB (red, green, blue)
Resolution: 72dpi (dots per inch)
Size: Generally smaller than 1920px and in KB (kilobytes)

Popular Web File Types:

2) Print Files

Built to be scaled & expanded without losing quality. Great for print but often large files that load slow on web and are too big for emails.

File Type: Vector
Color Space: CMYK (cyan, magenta, yellow, black)
Resolution: 150 – 300dpi (dots per inch)
Size: Often 3000px-4000px wide or high and several MB (mega bytes)

Popular Print File Types:

Color Space – Most people don’t know that web files and print files have different color spaces. Web files are built in an RGB (red, green, blue) color space which is much larger and vibrant than print files which are formatted in CMYK (cyan, magenta, yellow, black). The main reason is because colors on computers, phones and screens have light behind them which elevates the colors while printed colors on mediums like business cards, flyers, t-shirts or banners are a mix of the colors listed above. And when colors are printed on paper or fabric, they darken and spread which is why if you’ve ever seen a picture, image or design look great online but when printed it looks completely different, chances are it was created in a web color mode but printed in CMYK.

If you’re a designer, make sure your color mode is set correctly.

Resolution – One very important aspect to know about, not necessarily for the laymen but definitely for the designer, is resolution. This is also known as DPI (dots per inch) and in short, tells the file how many colors can be placed in a file per inch. Commonly, web files should be set and built with a DPI/resolution of 72 while print files can be built at between 150-300. That’s also why an image set at 500px wide at 72 dpi will be significantly smaller than the same image set at 500px but is 300 dpi.

Lower resolutions are great for web as they load faster and aren’t as big while bigger resolutions are great for print as they’re larger and print out much more clearly when scaled and expanded.

You’ll also see this with older vs newer computers. A 2011 iMac for example, has a much lower resolution than a 2019 Macbook Pro. So when a design is looked at on the iMac, it’ll look much bigger at 100% opposed to the Macbook Pro where 100% will look much smaller since the resolution is so much higher.

You’ll want to be sure to “Optimize” high resolutions images and “Save Them for Web” before either putting them on a website or attaching them to an email. (Free optimization tool listed in the resources below)

Size (Pixels & Bytes) – Finally, we’re going to look at size which is similar to resolution. Size isn’t as important for vector files because as you now know, vector files can be scaled and expanded without losing quality but it’s VERY important for web files because when a design or image is set to a certain size, if you blow it up or expand it even just a little, it will pixelate and lose quality.

For the most part, web images and designs don’t need to be much bigger than 1920px wide which is a pretty standard high definition width. Print designs and images on the other hand may sometimes get up to between 3000 or 5000 pixels. When you take pictures on your phone or with a digital camera for example, the raw or jpg files are very big. Sometimes thousands of pixels wide and high. And same with stock photography sites. Many times when you purchase a stock photo, it’ll be massive with an actual file size of several MB (mega bytes) which is the other piece to the equation with size.

Computer images and file sizes are measured in KB (kilobytes), MB (megabytes), GB (gigabytes) or TB (terabytes). There are lower and higher sizes as well but these four are the most common that you’ll see. Web files should ALWAYS be as small as possible in KB’s and with printed designs and high res images, you’ll often see those in MB’s.

So for example, if you take a picture with your digital camera and download it to put on your website, it could be 4000px wide and 6.5MB big. That is a huge file that will slow your webpage down dramatically and needs to be optimized before putting it online or sending via email. Again, be sure to “Optimize” your images and “Save Them for Web” before sending, attaching or doing anything with them online. A reminder that a free optimizing tool is listed in the resources below.

Wrapping Up:

In closing, one question you might have is “why would you ever even create a bitmap file if it distorts???”

Well, if you’re working on a website or with online graphics, generally your designs can be built much smaller and in the web color modes while if you’re creating, say a logo, that needs to look good on a website but also scaled big as a design on a billboard, then you’ll want to build that as a vector file. And with web files are being smaller, they don’t take up as much room on your computer.

Bitmap programs like photoshop do have additional advantages as they’re generally much more flexible and power when it comes to image editing, advanced graphics, etc, but I tend to do most all my designing in a vector program like Adobe Illustrator because those designs can be scaled and used for print if needed. One big thing to remember is that vector files can easily be saved down as web files for digital uses but bitmap files can’t be saved as vector or scaled up.

Well hopefully this overview of graphic and image file types has helped you understand the biggest difference between file types and more importantly how to use them moving forward. Below are some final takeaways and additional resources.

Image Optimization Resources:

• Free Image Optimizing/Resizing Tool – ImageResize.org
• How to Optimize Images for Web (for designers) – JoshHall.co
• How to Optimize Images for Web (for non-designers) – JoshHall.co

Additional Info:

• Different Types of Image Files – HubSpot
• Choosing the Right Image File Type for Your Site – Elegant Themes

You can also Google “image resizing or optimization tools” and you’ll get a plethora of options but for designers, Adobe Bridge or Photoshop is recommended.