What is raster and what is vector based image?When use what?

[quantum]

Here is a great article on the difference between raster based and vector based images and when to use what.

Quote:

Photoshop is raster based. Illustrator is vector based. You never do logos in photoshop unless everything you do is either on the web or in full colour - even then it's rare. If you use Illustrator, every line is just point connected with an angle of a curve, a vector. That way you can scale them to the size of the moon and you won't lose a single detail. If a curve is closed (both ends join) then you can fill it with a color. Many different closed curve layers on top of one another can imitate a graduated screen or color ramp like photoshop would do. You can't do really complex or photorealistic things in vector without spending days doing it, but in a logo you want simplicity anyway. Illustrator files are usually shared as EPS format. They're incredibly small and easily distributed over the internet because of their size. you only record the point on the lines, their angles and what color they are filled with which is usually much less data than a raster image. A raster image is made up of pixels (little squares) with a numerical value for their color. All the squares are the same size and places in a grid pattern. Each one needs at least three numbers (for RGB) to calculate it's color (4 for cmyk and 1 number for 8 bit colour like a gif) unless there is compression (like a gif, where large areas of the same color are assigned a beginning and an end point and the color value is assigned only once, or jpg's where an area of 8 or more pixels are assigned one of many algorithms built into the jpg codec). Raster images cannot be scaled up in size because they will look pixelated (like the image above) when printed. And files that are high enough resolution for the printing process are usually very large. We use these for photographs or completed files when we can output a raster image at exactly the size required for printing. As a vector, any colors can be assigned to the curves, including rgb, cmyk and spot colors. You could have a logo as pantone 567, pantone 490, 303 and more... In a raster you usually use a CMYK color model or RGB. Sometimes you'll run across a duotone or tritone but these are not very common and definitely will not be usable in most office programs. Gif and jpg are great for small office programs and for use in a little office type setting but for printing on a press, proper graphic design, signage etc. you'll need a vector based logo so that the outfit can work with it and have the cleanest image possible. You'll also need to be able to create logos that can be easily printed in one or two colours. Your clients might have a wonderful red-on-black 3D logo, but try printing it in the newspaper in one color and it will just be a solid black mush. As far as what you create for your clients - it's as simple as asking them. Do they just want a logo and they'll do all their own letterhead etc. themselves or do they want a full package? Charge accordingly. Sometimes if you just do the logo you can get more business by showing a sample of a card and/or letterhead design and telling you'll do additional design for only $X more. And sometimes you're just shooting yourself in the foot too!

Article taken from Graphics design forum.
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[emm]

Thanks for the useful information. This will come in handy. Usually most people do not realize how different the two medias are. The monitor and the printing media. For another thing, the web and the printing media are like exact oppposite. In web graphics we have to constantly worry about keeping the file size small. But for creating a graphics that will print, as much information, bits and bytes we can get it is as better.
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