Photography: A Glossary of Imaging Terms

EPS? JPG? TIF? PSD? Does your brain just feel scrambled sometimes trying to figure out all the different imaging terms out there and what they mean? There are so many image formats in the digital world. In Photoshop alone, I can save in any one of 19 different formats and I’m not embarrassed to admit that, even after 20 years of Photoshop, I still don’t know what some of them are and have no idea what anyone would use them for. So, I won’t be defining all those esoteric formats that most of us are never going to use. Today’s post is about the most common imaging terms. The ones we image geeks most often use when talking about graphics–and hopefully, the ones that are most useful to those of you who aren’t image geeks.

Let’s start with the two most general categories of digital images—nearly all digital images fall into one of these two categories.

RASTER: Raster images are resolution dependent, meaning you can only enlarge them so far or they will begin to deteriorate or pixelate and lose quality. Photographs and photo-realistic images are probably the most common raster images.

VECTOR: Vector images are based on a geometric formula that allows them to be displayed smoothly at any display size. They do not lose quality when they are enlarged as Raster images do. Illustrator images are generally vector images.

The next group of image formats is raster based.

BMP: Windows Bitmap format. These are uncompressed files and is Windows’ preferred format for handling graphics. It is not a format that is regularly used in graphic design or photographic image work. These are usually used in system graphics or as part of the subsystem for other graphic systems.

GIF: Graphics Interchange Format. GIF is good for storing simple graphics with relatively few colors, including things like logos and cartoon-type images. GIF also supports simple animations and is often used online for these. GIF uses a lossless compression and can maintain small files sizes for images that do not have detailed color. Detailed images stored as GIFS will be very large and often unwieldy files sizes. GIFs are not recommended for photographs.

JPG/JPEG: Joint Photographic Experts Group. It is a compression method. JPG is the default image save setting for nearly every digital camera. JPG files are easily sharable and the preferred file format for most commercial photographic printing services. While they are superior to EPS images for conveying photographically realistic images, they are limited as far as how much you can enlarge an image without loss of detail.  If you try and make a JPG much bigger than the size you started with you will begin to see definite deterioration and loss of quality in your image. JPG compression can significantly reduce file size, which makes it a great format for sharing images and graphics on the web. Be aware, however, that too much compression can lead to a noticeable loss in quality. And saving and re-saving a JPG file can also result in loss of quality.

PNG: Portable Network Graphics. It is not a GIF but a raster file format that supports loss less compression. It was designed as a replacement for GIF and is probably the most-used lossless format on the internet.  It was designed for internet and not for print use so you’ll only see PNG as RGB color space. (One of the things I like about PNG is that I can save it with a transparent background, making it useful on some web posts).

PSD: Photoshop. It is a proprietary format and may contain multiple layers. Like JPG images, it is pixel-based and is limited as far as how much you can enlarge an image without loss of detail.

RAW: Raw refers to image data that has not yet been processed. Many digital cameras offer the option of creating in RAW format. In order to print or edit these images, you will need to convert them to one of the other image formats. The advantage of a RAW image is that all possible data that can be collected in the image is present. I create all of my professional photography in the RAW format as it is the most flexible and offers the most options for post-processing.

RIF: Corel Painter Raster Image File. This is the proprietary file format for Corel Painter and produces a Raster image. The painterly effects are saved separate from the “canvas” so it has layers of a sort and creates a fairly large file, perhaps akin to a PSD file in size.

TIFF/TIF: Tagged Image File Format. It was originally designed as a common format for early desktop scanners so manufacturers would use a common format instead of competing proprietary format. It is one of the largest file formats.  It is excellent for making high-quality, large format prints. Because of its large file size, it is not a good choice for internet use. TIFF is usually a lossless format, though there are lossy TIFFs.

These formats are vector based.

AI: Adobe Illustrator. This is a proprietary format, the default saving format for Illustrator images.  AI images are vector-based.

CDR: Is the proprietary format for CorelDRAW, Corel’s equivalent to Illustrator.

EPS: Encapsulated Post Script is vector format, can be enlarged without limitation and without loss of quality. Vector images are saved as mathematical coordinates instead of pixels, which means the relationship of the coordinates doesn’t change when you are enlarging or decreasing the size of the image and you don’t lose any quality. (Yeah, my eyes glazed over a little at that explanation, too–just remember the last part about not losing quality when you change size.) EPS files can be opened in Photoshop, though Photoshop needs to convert them first. They are more commonly used in Illustrator projects.

PSP: Proprietary format for Corel’s Paint Shop Pro, which is a photo-editing program you could compare to Photoshop in purpose.

SVG: Scalable Vector Graphics. These are most commonly used as a vector format for the web. They can be automatically resized in web apps using a script.

Other Image Definitions

PDF: Portable Document Format PDF is often used to share documents across computer systems and platforms. It displays documents in a format that is consistent regardless of applications or operating systems.  PDF’s can be used for text, graphics and other information. PDF is neither a raster nor a vector since it is not strictly an imaging file, but can be used for different kinds of information.

POST-PROCESSING: This refers to anything you do with a photograph AFTER you’ve taken it and downloaded it to your computer. This could be color adjustments, retouching, cropping or any other type of manipulation.

LOSSLESS: Data compression techniques that result in no loss of data, meaning no loss in quality.

LOSSY: Data compression techniques that can result in some loss of data, depending on the amount of compression.

Finally, definitions for the two most common color spaces.

CMYK: CMYK is also not a file format. It stands for Cyan, Magenta, Yellow and Key (meaning black). Like most people I just remember that the last letter in black is K and they use it to avoid confusion with blue (which may or not be true, but it has always worked for me). These are subtractive colors and CMYK is the format used in traditional printing. If you own a color printer, you will likely recognize these as the four colors of ink or toner your printer uses. Unless you are preparing image files to send to a commercial printer, you will generally not work with your images in a CMYK color space.

RGB: While not a file format, RGB is a common imaging term. It stands for Red Green Blue, the three additive primary colors and is what is used to create color in the digital world. It actually predates computers. Televisions, computer monitors, projectors and cameras all employ RGB technology.

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Are there other digital imaging terms you’ve heard and don’t understand? Please share them in the comment section below and we’ll add to this glossary.