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Image File Formats

CONTENTS

Introduction

There are many different formats for storing graphics. The two main types are vector graphics and raster (or bitmap) graphics.

Some of the formats are lossless and have no compressions such as all the vector formats and the TIFF and GIFF formats. All the others use compression to reduce the file sizes. Reduced file sizes are great for the internet to reduce transmission times (When a website takes a long time to download because of graphics that are large, for example). Also reduced file sized allows for more pictures to be stared in the same size storage media.

One of the best compressions algorithms to date has been the JPEG system. It can reduce the file size dramatically without much distortion - most people cannot tell the difference with family photographs even when the file size has been reduced to a quarter. Recently the HEIC system has provided an even more efficient compression but it has not yet been accepted be the browser community.

The down side to compression is that information is lost and the picture is less accurate than the uncompressed picture. How much this matters depends on the user and the purpose of the graphic.


About Vector and Raster Files

Graphics fall into to two main categories:

The difference between these two types is what they're made up of. Vector graphics are made up of lines and curves with very specific starting and ending points. Bitmap graphics are made up of little squares called pixels that remain the same no matter the scaling when resized.

Here is a very simple image made up of a red circle and a black line: graphic


Notice that even blown up this large (1600%), it's still fairly smooth when displayed as a vector. You only see a little bit of jagginess because your monitor can only display this graphic using pixels. If you were to print it out, you'd see that it's as smooth as the same graphic at 100%...

graphic

Here%s the same image - except it's a bitmap graphic - blown up by 1000% (a lesser amount than the vector image above). Doesn't look the same does it? You can see obvious jagginess or "stairstepping".

graphic

Basically, when you enlarge a bitmap graphic you'll notice pixelation (jaggies or stairstepping shown above). That's because the software has to guess where to put the extra pixels. Using "dithering" may provide some apparent reduction of the jaggies.

When you reduce the graphic, the software has to decide which pixels to throw out. Both the addition and discarding of pixels in software using interpolation.


Raster File Formats

Raster or Bitmap files contain information about each pixel in the image. A pixel is a single dot. Every pixel is included in the file. The quality of the image depends on how many pixels per inch the device (computer screen, TV screen, smart phone, printer, etc.) can provide.

Here are some details on the seven most common formats:

JPEG (and JPG) — Joint Photographic Experts Group

Strictly speaking JPEG is a compression algorithm and JIFF is the file format, but the files are usually called JPEG files. Thay are:

PNG — Portable Network Graphics

GIF — Graphics Interchange Format

TIFF — Tagged Image File Format.

BMP — Bitmap.

HEIF — High Efficiency Image File Format

HEIF, short for High Efficiency Image File Format, is an image format developed by the team behind the MPEG video format to be a direct competitor to JPEG.

In theory, the compression is almost twice as efficient as JPEG, leading to images of up to double quality with identical file sizes.

It’s a raster image format, based on pixel mapping, meaning you cannot scale up the images without losing quality.

Raw Image File Types

Raw image formats are the file types a digital camera uses to store full-quality images for later post-production and editing.

Major raw image file types by camera maker including Kodak: CR, K25, KDC, Canon: CRW CR2 CR3, Epson: ERF, Nikon: NEF NRW, Olympus: ORF, Pentax: PEF, Panasonic: RW2, Sony: ARW, SRF, SR2.

RAW files offer up to 16,384 shades per color channel (14 bit) in a single picture. That gives you more flexibility when tweaking colors and contrast in post-processing. Raw images aren’t meant for the web or sharing and aren’t supported by any major browser or image viewer.


Vector File Formats

Vector files are images that are built by mathematical formulas that establish points on a grid. Raster files are composed of the colored blocks commonly referred to as pixels. Because they can infinitely adjust in size without losing resolution, vector files are more versatile for certain types of tasks than raster files. THey are also very much smaller. The most common types of vector files are:

AI - Adobe Illustrator

This file is commonly used in print media and digital graphics, such as logos.

EPS - Encapsulated PostScript

This an older type of vector graphics file. They do not support transparency in the way more modern file formats do.

PDF - Portable Document Format

This file type is built for the exchange of documents across platforms and is editable in Adobe Acrobat. It can contain vectors (including text) and rasters.

SVG - Scalable Vector Graphics

This format is based in XML (a markup language used widely across the Internet that's readable by both machines and humans). It’s useful for the web, where it can be indexed, searched, and scripted.

CDR – CorelDraw

The CDR file format was originally developed by Corel, the makers of CorelDRAW (a popular alternative to Adobe Illustrator). However, it’s now a universal format supported by many programs.

All the formats

All the file formats that can be read and translated by the application GraphicConverter :

There are 96 in this list. Many of them are very specialized and MAGIC members are unlikely to encounter them. Some are old and no longer used bur appear from time to time in old data sets. I have seen Macs that still have PICT files on them.

For more information on this subject see: this website at Kinsa.com.

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last updated: 26 May 2024