The difference between raster images And vector Graphics

RASTER IMAGES
Raster or bitmap images are continuous-tone images that are constructed as a continuous mapping of pixels. These Images can not be scaled, rotated or skewed outside an image editing application without the loss of reproduction quality.

The quality of the raster images depends on the resolution and the dimension.
- The resolution determines how many pixels are there per inch and is measured in ppi (pixels-per-inch) The most preferred resolution for screen is 72ppi and the best resolution for print is 300 ppi.

- The dimension is determined by how many pixels are on the width and the hight of the image. e.g. 5605 pixels wide by 3757 pixels high
Once the image is created at a certain dimension, you may not be able to use this image at a larger size without losing quality.

The most used program for editing bitmap images is Photoshop. When you are exporting your images you have to take into account the purpose of use.
For on-screen viewing you can export to JPG, GIF, PNG,
For printing export to PSD, PDF, TIF

The Photographs are the most common example of a raster images. However when the vector graphics are resterized (converted into rasters) this automatically turns them into pixel comprised image and are treated like a raster image.

The colour mode is usually RGB used for on-screen editing or CMYK used for printing.

VECTOR GRAPHICS
Vector graphics are hard edged images created in a drawing program. Because they are based on mathematically defined lines and curves, they can be manipulated and scaled without loosing reproduction quality. The dimension of the Vector files and graphics is measured per dots and is called dpi (Dots-per-inch)
Vectors can be categorized in the following Lines, (Curves)Outlines and Fonts
- The vectors made in lines are object created with the thickens of the line. This means when you scale them they will change proportion and relatively size. It is recommended when working with lines before exporting the file to convert them in curves. However keep a copy of the lines in case you would need to edit again.

- The vector made in curves is actually an outlined object. Each element is shaped by the outer lines (fig..) This is the type required when used for print.

- The fonts are vectors itself however they are connected to an install software file that determines the font type. Without this file the desired font wouldn’t appear in the correct shapes. The solution is weather install the font file or outline the font in 2 easy steps within the vector editing program.

VECTORIZING AND RASTERIZING

It is important to know that it is easy the vectors to be converted in rasters - the process is called rasterizing. However the other way around is more difficult. Converting Raster images to Vectors is called Vectorizing and can be done in two ways.
- The proper way is to draw the graphic with the appropriative programme tools this means outlining every inch by hand. The process takes time especially if the objects are more complicated this is why designer artists usually do that for a nеgotiated fee.

- The other way of vectorizing is automatically generated by the editing programs and is usually applied on simple objects. The program mathematically generates the lines depending on the sharpens of the image but this method is not recommended if you need precise outlined graphic.

COLOR MODES FOR PRINTING

The colours applied on the vectors are spot colours and are usually used in limited amount. When exporting your file for print every colour of the vector graphic has to be determined in Pantone spot colour mode. The Pantone Colour Matching System is largely a standardized colour reproduction system. By standardizing the colours, different manufacturers in different locations can all refer to the Pantone system to make sure colours match without direct contact with one another.
However for on-screen purposes you can use other colour mode systems such as CMYK and RGB

The vector editing programs are typically Adobe Illustrator, Corel Draw, Inkscape and when you export your files formats are EPS(AdovePostScript) Ai(Adobe Illustrator), CDR(Corel Draw)

HERE IS THE CHECK LIST YOU HAVE TO FOLLOW WHEN YOU PREPARE YOUR FILE FOR PRINT!