There are two basic formats for pictures: Vector and Bitmap.
Vector images are made up of many individual, scalable objects. These are defined by mathematical equations rather than pixels, so they always render at the highest quality, even when enlarged. - They are typically used for images such as logos.
Bitmap images are made of pixels, each with a colour value. The bigger the picture, the more pixels are needed. If images are scaled up, quality is lost. - This format is used for photographs.
Vector = Logos / illustrations = Scalable
Bitmap = Photographs = Pixels (non-Scalable)
When having a Logo designed, request the following versions:
EPS = The Original (Vector = Scalable)
JPG = Website's and Social Media (Pixels = non-Scalable)
PNG = Version with a transparent background (Pixels = non-Scalable)
EPS (Encapsulated PostScript).
A distinction must be made between vector EPS, which is scalable, and Photoshop EPS, which is just a bitmap image. EPS is a vector format designed for printing to PostScript printers and imagesetters. It is considered the best choice of graphics format for high resolution printing of illustrations. EPS files are created and edited in illustration programs such as Adobe Illustrator.
JPEG (Joint Photographic Experts Group).
JPEGs use 'lossy' compression to dramatically reduce the size of bitmaps. This degrades images, which makes the format unsuitable for print work. JPEGs are a common standard for electronic delivery (digital cameras or web).
PNG (Portable Network Graphic).
A PNG, is an image type that's commonly used in web design to provide a transparent background and/or a semi-transparent image. PNGs are often saved versions of logos as the image can be easily placed over a background of a picture, block of colour or pattern.
TIFF (Tagged Image File Format).
is the most flexible and reliable method for strong bitmapped images in various resolutions, grey levels and colours. Tiff was created specifically storing greyscale data, and it is a standard format for scanned photographs. It can be compressed with it's own LZW compression which is 'non-lossy' (no data is lost on expansion).
GIF (Graphic Interchange Format).
is CompuServe's standard for compressed web graphics. It is a bitmap format which allows transparency but a limited range of colours.
PDF (Portable Document Format).
Developed by Adobe, PDF is a computer file format designed for publishers to distribute electronic documents. PDF is related to the Postscript language, and may be used with text, image (bitmap & vector), and/or multimedia files.
They are created by making the original document into a PDF file which can then be viewed on almost any computer. The exact layout, font attributes, and formatting of the document are preserved. PDF files may be used for displaying information on the web or for delivering artwork ready for print.
PDF files are viewed with Acrobat Reader, which is supplied free. To create the documents another program must be bought. - Acrobat which 'distills' a postscript print file into a viewable document.