Tag Archives: bitmap format

Understanding File Formats: Bitmap vs. Vect

Just what the heck is image formatting, and why should you care?

Your printer wants 300dpi images in JPEG format, your webmaster needs a 72dpi GIF and the sign company needs your logo in an EPS vector format…sound familiar? If you’ve struggled to understand why you need sixteen versions of your logo when they all look the same, then read on.

Image file formatting is something every DIY marketer should know. Whether you’re creating your own graphics, or just trying to keep track of the corporate identity, a basic knowledge of computer file types is important.

When you save a digital image or graphic there are several formats available. The most commonly used in everyday business are JPEG, EPS, TIFF and GIF. Learn when, why and how, to use these file formats correctly and you will save time and hassle when working with designers, printers and other service providers.

Bitmap vs. Vector

File formats all fall into one of two categories Bitmap (also known as Raster) or Vector graphics. Understanding this simple difference will go a long way in knowing how to save your files correctly.

Bitmap files are made up of little squares called pixels, which when assembled in a certain order make up the final image. Think of it like a puzzle where each piece is a single color. When put together in the right order, those pieces make a picture. The number of pieces in that puzzle determines the size of the file, as well as the resolution. Which brings me to dpi.

What is so important about dpi? It determines the resolution of your image. A 72 dpi image has 72 dots per inch. Imagine that you have a finished puzzle that measures 8×10 and has 72 single colored pieces. Now imagine what would happen if that same 8×10 puzzle had 300 pieces. Your image would be sharper and possibly include more detail. When viewing at the same distance the colors would blend more seamlessly into one another thus giving you a clearer image. That’s the difference a few hundred dpi makes. That’s why resolution matters. If you want to avoid the jaggies or becoming pixelated, then leave the 72dpi images for web use only, and for print choose 300dpi or higher.

JPEG and GIF are the most common bitmap formats. GIF is used primarily for the web. To be honest, my experience is print based, so I have little use for GIF. (Not that I’m slighting the GIF devotees out there, I just don’t use it much). In fact, bitmap images can be saved in many other formats, including TIFF and EPS. So you’re probably wondering, what’s the difference?

It’s all about compression. When I first started working on the computer to do graphic design and layout (as opposed to pre-computer hand-cut paste-up) I found a quick and easy way to understand the difference between JPEG and TIFF. JPEG is a lossy format. Not ‘lousy’ but ‘lossy’. This means that each time the file is saved, it is compressed. In order to do make the file smaller it selectively loses data. Whereas TIFF is a lossless format, meaning it is generally uncompressed and stores all the original data. TIFF can also preserve any layers for future editing, while JPEG images must first be flattened.

JPEG was created for photography, which explains why most digital cameras use this format. But as technology continues to improve other formats like RAW are also showing up as options.

So if photographs and detailed images are generally saved in bitmap formats, then what use do we have for vector formats? Plenty.

Vector images are made up of points, lines and shapes instead of pixels. While it would be extremely difficult to reproduce a photograph in vector format it is perfect for simple graphics, like logos. One of the best advantages of vector graphics is the limitless potential for manipulating the image without losing clarity. For example a logo created in a vector program, such as Adobe Illustrator, could be scaled from business card to billboard and remain just as sharp. And, believe it or not, the file size wouldn’t be much different.

It’s also important to note that not every program can OPEN every file type. You’ve probably discovered this on your own, but it bears noting. This is especially true of vector formats like EPS. Vector files are saved and read by the computer through a set of mathematical instructions. If you try to open an EPS in Microsoft Word it won’t work. That’s because Word doesn’t interpret those instructions. But don’t despair. If you need to view the graphic, but not edit it, you can often import or ‘place’ a vector file into a word processing program.

Hopefully understanding a few of these basic facts about image file formats will make your life a little easier next time someone asks for your logo or requests a photo of your latest product.

For a detailed description on the difference between bitmap and vector images check out this link.


Posted by on August 2, 2009 in Design, photography


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