Do You Know Your Graphics File Formats? Part One: Raster Images

half tone eye raster image

Chances are you have had to deal with logos or graphics at some point in your career. For the vast majority of people posting online, that’s usually a JPEG or JPG file. Even if you only casually post photos to social media such as Facebook or Instagram, you are aware of what a graphic file is. In this article, we’ll talk about the most common graphics file format: the raster image.

Raster Graphic Image Files

A photo is a “graphic” and is the most common file being posted to social media. The source of this type of graphic is more than likely coming from a digital device, such as a smartphone or even a DSLR (professional digital camera such as from Canon or Nikon, etc.) Whether the photo is taken on the fly using your cell phone or technically set up in a photographer’s studio, they are both essentially the same file format. These are what we call raster images. By contrast, vector images are smoother. We’ll talk more in depth about vector images next month.

A raster image is a type of file format composed of bitmaps. Bitmaps are tiny coded squares of color that appear grid-like if you were to view them extremely close up. Collectively, these bitmaps form the images in continuous tone graphics, such as photos. A raster image is best for photographs and images requiring smooth color transitions.

Low-Resolution Image Files

Have you ever heard of the phrase “that photo is low-res”? The unfortunate thing about raster images is they are potentially susceptible to degradation when you enlarge them or even save them. If you’ve ever seen a photo that appears with lots of jagged edges around the subject matter and throughout the image itself, there’s a chance the image was enlarged beyond its original pixel dimensions. Such an image is referred to as low resolution.

For example, if you take a thumbnail image (a tiny preview image for example) and enlarge it too much, it will be low resolution. The rule of thumb is this: you can take a small picture and make it smaller, but, in general, not take a small image and enlarge it.

thumbnail artwork

This is an example of a small thumbnail graphic.

low resolution graphic

The same thumbnail artwork with extreme file degradation. This is very low res!

The Dilemma of Saving Raster Files

Beware: saving the same JPEG file continuously over itself can degrade the quality of the image. That’s because the JPEG file format generally compresses the image to save file size from getting too large. This is accomplished by removing data from the file itself to become even smaller in file size. This can happen each time you re-save a photo back onto itself. If you remember photocopiers and the idea of making a copy of a copy of a copy…well, that’s what’s happening. With each save, you can potentially degrade the image quality.

This may not be an issue if you are posting online socially such as to share between friends and family. But, if you are a working professional in a number of fields relying on high-resolution raster files, you will want to make sure you are using high-resolution raster images for professional output.

Raster Images Rule the World Wide Web

Raster images are what you are seeing, by and large, when you are online. From photos to logos, almost every image on the world wide web is a raster image. There are so many different types of raster files, but here are some of the most common ones:

  • JPEG (as mentioned above)
  • PNG
  • GIF
  • PSD

Almost any type of document can be rasterized. One can take a document such as a Word file, and export it out as a JPEG. The same for probably any other type of program that has a “Save as JPEG” export feature. The advantage to this being that a JPEG is a type of file format that virtually any device today can open and view. In this way, a raster file such as a JPEG can be easily shared with anyone, almost anywhere. Raster images rule the world wide web. Almost all of the images in a Google image search are raster images.

Raster Images with Transparency

If you are looking for a raster image that does not have a white background, such as for an online logo, then you need to save your file in a format that supports transparency. One of the most common file formats for this is PNG (Portable Network Graphics). 

graphics with transparent background example

This file format supports raster graphics that allow for a clear background. This means you can have your logo overlap with other objects without a white box appearing around the logo. PNG is another common file format used online.

Raster Images and Print

printing pressRaster images are also converted into graphic files that can be made to print for commercial printing. If the raster file (photo) is of really high quality, it can be converted and accepted for high-quality printing. 

Today, all images are in one way or another converted to raster files. Even a large traditional oil painting has to be photographed. If the photo of the oil painting is analog (taken with film), that photo would need to be scanned into a computer, manipulated to be processed in a digital print workflow, and finally printed. It doesn’t matter if the press is digital or offset, the source file is raster. This is because the commercial print world has become increasingly digital in its workflow. High quality, raster images are a must for successfully going to print.

And, if you need help with your photos (raster images), Rock Star Marketing is here to assist you. We have commercial printing and prepress knowledge and experience of over 20 years. We can also help with creating raster/bitmap images that are ideal for online use.

Next month, we’ll be talking about another popular file format: Vector files. Be sure to check back here next month or follow us on social media to be notified when our latest blog post is up.

Call Rock Star Marketing at (408) 833-9868. Or contact us using the button below.

Take Our
Social Media
Scorecard Quiz

Take our quiz to see how you score on using Social Media to promote your business. We’ll email you your results directly with actionable steps you can take today!