Best Image Formats for Email Signatures

Images come in many different file types, each having their own distinct advantages and disadvantages. Fortunately, there are currently only three types that are commonly used in email signatures making the choice a bit easier.  

Although one of these three is universally considered the overall best, or at least the go-to for email signature images (which will be revealed later on), each of them can be used depending on requirements. 

Here are some terminologies that will be used when talking about image file types to help smooth things along:

• Colors – For digital images, this literally defines how many colors a given image file type can support/represent.
• Compression – This is the process of reducing the file size of an image as compared to its original form while not negatively affecting the image quality too much.
• Lossy – An irreversible compression method that involves sacrificing image quality for a significantly reduced file size.
• Lossless – A compression method that reduces the file size of an image without sacrificing quality.
• Pixels (Picture Element) – It is the smallest element that makes up an image and is normally indistinguishable by eye. More pixels mean finer image details and better quality.
• Pixelation/Pixelated – A state of an image where its pixels are distinguishable by simply looking at it. This normally occurs when an image is upscaled as the pixels are magnified or lossy compression is used.
• Scaling – The resizing of a digital image in terms of dimension size (length and width). Normally measured in pixels.
• Downscale – The decrease of a digital image’s size.
• Upscale – The increase of a digital image’s size.
• Transparency – In simple terms, this is a functionality that allows an image to have transparent parts either by index or alpha channels.
• Index – A color can be set to either be transparent or opaque but nothing in between. Often causes jagged edges around the image.
• Alpha – Similar to Index except it also allows varying degrees of opacity/transparency. It does not cause jagged edges around the image.
• Graphics – These are images (re)produced by a computer and visually displayed on a screen.
• Raster – Images that are (re)produced by arranging pixels in a grid of colored squares (also known as a bitmap). Best suited for photographs or images with a lot of color and detail.
• Vector – Images that are (re)produced using a set of points and lines (also known as vectors, hence the name) based on mathematical formulas and graphs. Best suited for icons, logos, and illustrations.

In the early 90s, the GIF format was under a patent which effectively meant that a fee was required in order to use it. This drew a lot of criticism from users at the time which eventually led to the creation of the PNG format. This new (raster graphic) format provided users with a free alternative to the popular GIF.

As an alternative to GIF, it does share some of its features but with welcomed improvements. Modern PNG uses lossless compression like GIF but produces smaller file sizes when comparing both formats of the same image. It also supports both indexed as well as alpha transparency which greatly improves versatility. However, it does not support any type of animation.

PNG also stacks up pretty well against JPEG. Like JPEG, it can support up to 16 million colors making it great with photographs but unlike JPEG, it is also well-suited for images with text due to lossless compression. Although it does produce comparatively larger file sizes, its versatility greatly outweighs this making it a suitable option for any type of image.

The PNG format has three types:

1. PNG-8 – Supports up to 256 colors and is great with simple images and graphics while having small file sizes.
2. PNG-24 – Supports up to 16 million colors and is great with photographs or images with a lot of color. The resulting file size will be large.
3. PNG-32 – Supports more than 16 million colors and is mainly used for complex images and graphics. Not really suited for email signatures due to producing very large file sizes.

VERDICT: Overall this is one of the best image formats for email signatures due to its versatility and lossless compression. Do take care when using large file sizes as it greatly slows email loading times.

Pros: 

• Great image quality relative to file size (lossless compression)
• Smaller file size (compared to GIF)
• Smooth image transparency (Alpha)
• Great with most types of images and even text

Cons: 

• File size increases with image quality
• No animations
• Slow loading time for large image files
• Cannot be upscaled without pixelation

First off, the most commonly used digital image format available today, JPEG or JPG. Named after the same group that created it, its main purpose was to compress digital images that were produced via digital photography.

JPEG is a raster graphic that uses the lossy compression method which allows it to achieve smaller image file sizes with an acceptable loss in quality. This, in turn, makes the images take up way less space and allows faster loading times on web pages and emails.

In addition to this, it can support up to 16 million colors making it well suited for full-color photographs. Colorfully detailed photos also mask the pixelation caused by the lossy compression quite well making it almost a non-issue. It can even strike a balance between file size and image quality (adjustable during editing) making it rather flexible.

Unfortunately, the resulting pixelation does make it a poor choice for images that have well-defined curves, edges, lines, and/or text due to the distortion it creates. This includes most logos and icons used today. Transparency is also not supported so the resulting image will not be well-suited for things like dark mode on devices. Animations are also not possible using JPEG.

VERDICT: For email signatures that include a full-colored photo, JPEG is a great option. Apart from this, the PNG format is better.

Pros: 

• Can achieve very great color depth
• Great with full-colored photos (up to 16M colors)

Cons: 

• Degraded image quality/pixelated image (lossy)
• Terrible with text and/or images with defined curves, edges, and lines
• Image transparency is not supported
• No animations
• Cannot be upscaled without pixelation

The Graphic Interchange Format or more commonly known as GIF is chronologically the very first image format created for the purposes of displaying and sharing images on computers while also saving memory, hence the name. This was approximately four years before the World Wide Web was even made publicly accessible.

Although it is also a raster graphic like JPEG, it is not well-suited for photographs due to only supporting up to 256 colors. It also does not compress images to the same extent as some other formats, resulting in larger file sizes. This caused it to often be overlooked when it comes to still images.

However, it is not all bad for the GIF format. One of its biggest advantages over JPEG is it utilizes the lossless compression method allowing relatively small file sizes while not compromising image quality. This is especially great for simple images, text, logos, and monochrome icons as pixelation is non-existent in most cases. Plus, it also supports index transparency which allows the image to adapt to whatever background is used.

Its most defining feature is its ability to support animations which has seen widespread use all over the internet and is why most consider it the best format for images in general. Even email signatures can incorporate GIFs though caution is advised as not all email clients and apps support this image format completely.

VERDICT: Email signatures can benefit from this format if simple images are used due to it having lossless compression. The animation feature is also great but not being supported by all email clients is a bit of a letdown.

Pros: 

• Good image quality relative to file size (lossless compression)
• Great with logos, icons, and text
• Image transparency (Index)
• Animation support
• Relatively quick loading time on web pages and emails

Cons: 

• Not good with photos (limited to only 256 colors)
• File sizes are comparatively large
• Transparency can cause jagged edges
• Animations are not supported by all email clients
• Cannot be upscaled without pixelation

There are of course lots of other image formats available, such as WebP, SVG, TIFF, and BMP, but we left them out of this list because they likely fall into the below criteria:

• Aren’t fully supported by all email clients – this would have devastating effects when sending an email to your recipient who has an email client that doesn’t support that specific image format. The recipient would simply see a red cross where the image is normally shown. Not a good look.
• Aren’t suitable for web use – an example of this would be BMP images which have little to no compression, meaning they would take a long time to download.
• Require specific software to be viewed – Adobe Photoshop (PSD) files that aren’t compressible and require Photoshop to be installed, making them impractical to use since not everyone has Photoshop installed.

Naming the best image formats for email signatures is not easy (nor realistic) given the varying conditions that need to be fulfilled. Each has its own advantages (JPEG for photo clarity, GIF for animations, and PNG for transparency and compression) that would make them great in certain situations. But they also have disadvantages (average compression for JPEG, limited colors for GIF, not so great color depth for PNG) that would make them unsuitable otherwise. If there is no rush, then taking the time to weigh the pros and cons of each will help make an informed decision. 

However, if you need to make a quick (but safe) decision, then PNG is probably the best image format to use for email signatures. It’s great with any image regardless of whether it is an icon, logo, or photograph. It provides great quality relative to its file size and offers image transparency if needed. It is also widely supported by all major browsers and email clients used today. Hard to go wrong with PNG when looking for the best image formats for email signatures.