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Inkscape User Manual

Un-official manual by Kevin Wixson

Table Of Contents


Part I. Inkscape
Chapter X. Vector and Bitmap

Vector and Bitmap

Inkscape is a vector editor, not bitmap (raster) editor. What does that mean?

The majority of images stored and processed on computers today are bitmaps. A bitmap is a very low-level abstraction. It stores information about the color (and transparency, possibly) of every pixel of the image - but nothing else.

For example, if you have a JPG format image with a black circle on white background, in fact there is NO black circle stored in the image at all: it is only the person viewing this image who perceives that it displays a circle. A human viewer interprets the whole image and "sees" a circle. In our minds we group all of the adjacent, similar looking (black) pixels together, and we associate the group of pixels with the shape of a circle. All that the computer knows about the image is that some of its pixels are black and some are white.

As a result, there is little the computer itself can do with such an image. It can paint all white pixels blue, but it cannot move or transform the circle because it does not "see" it. These kinds of tasks may be difficult even for humans, as anyone who has used The Gimp or Photoshop would attest: you will have to use complex and unreliable tools to "select" the circle, and you still cannot do this perfectly if, for example, the edges of the circle are anti-aliased (i.e. smoothed so that some pixels are half-black, half-white).

Vector graphics are different. In a vector format, the actual circle can be stored, along with its properties, as an object. In vector graphics, the image is represented as a series of instructions to the computer to, for example, draw a line from point A to point B with this arc. Each individual point along the path is not described in the digital file. Only the two points and information about the characteristics of the line to be drawn between them are described in the file. This is what makes vector graphics "scalable." In order to change the size of the image you simply change the scale of the measurements that describe where point A and B are located. When you change the scale, they are further apart or further together, but they are in the same position relative to eachother. The information about how the line between the two oints remains the same, so it is drawn on the screen or on the paper in the same way, even though the points are in different places either further apart or closer together.

This means you can easily separate any object from other objects and do whatever you please with it. Moreover, computer can do a lot of things automatically! No more frustrating "selections", just pick any object and edit it as necessary. That's how Inkscape works, and that's its main point of difference from bitmap editors such as The Gimp.

Here are the main advantages of the vector approach:

The only downside of vectors is that you are limited by the types of objects and properties that your drawing tool and vector format support. While you can store arbitrary graphics (e.g. photos) in bitmaps, you cannot easily simulate very complex graphics with vectors. Still, with Inkscape's gradients and transparency, you can create amazingly photorealistic vector images. Note also that, as a higher-level abstraction, vector may include bitmaps as a special kind of object. Thus, you can insert a photo into an Inkscape drawing and combine it with any vector objects.


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Disclaimer

This manual is my scratch pad and development site for the Inkscape documentation project. Documentation that appears here may eventually work its way into the official Inkscape documentation, and changes to the Inkscape documentation may work it's way into this draft. It is a work in progress, so please don't mind the mess. Anything that appears here is GPL'ed under the usual licenses for GPL documentation, yada, yada, yada, or has been dedicated to the public domain. For a list of those elements that have been placed in the public domain, please click here.

Links To Official Inkscape Resources