What does rasterization do to an image?

Question

What is the general purpose for making or converting graphics / images to a raster format?

What happens to an image when it is rasterized?

Answer 1

Without knowing what kind of image you are rasterising, this is kind of a shot in the dark. Yet, here goes:

Rasterisation does exactly what the name suggests: making an image into a raster image, also known as a pixel image or bitmap. Rasterisation is usually done to vector graphics or images that have vector components. Vector components can be things like text objects that haven't yet been rasterised: the letterforms are vector images.

Examples of vector images are .ai, .eps and .svg files. Examples of images that can contain vector elements are .pdf and .ps. InDesign files (.indd) are also combined raster and vector elements, but .indds are not meant to be distributed to a printer or somesuch: you'd export a .pdf copy of them first. Examples of raster images are .tif and .jpg files.

Rasterisation usually reduces the image to one flat layer, and thus limits editability to a minimum. You will want to keep a non-rasterised version of your file archived at all times, just to make adjustments later, if necessary.

Answer 2

Rasterization can mean different thing in different contexts:

• In contexts of vector graphics it is the process of turning vector images into pixel images.
• In context of printing it has a similar meaning but to convert into atomic printer operations.
• In context of 3D graphics it means one special kind of processing where the polygons are either diced or pleated and slapped either with or without sorting to the frame buffer. In general scan line rendering is usually a rasterizing algorithm while a ray tracer is not, hybrid engines do exist. Although the term may be used interchangeably.

Answer 3

It means to convert a vector graphic (a graphic made of lines and curves with infinite quality) into a pixel image, that you can only zoom in so much until you start to loose quality.

Raster formats: JPEG, EXIF, TIFF, RIF, GIF, BMP, PNG, and lots more

Vector formats: SVG (Scaleable Vector Graphic, most common), CGM, Gerber format (RS-274X)

If you are not using Illustrator or are not aware of what a vector illustration is, you most likely aren't using one. To check for sure, zoom in on the image and if the pixels become defined, you are looking at a raster image.