Why are BITMAP files larger than VECTOR files?

Answer 1

Bitmap files are bigger for two reasons, first BMP is an abbreviation of bitmap and every bit in the picture is mapped. Second Jpeg files are compressed using a lossy compression algorithm so some information is discarded. This is why you lose quality when you save a .bmp as a .jpg. In fact, every time you edit and save a Jpeg file, you lose more information, leading to a constant degradation in quality.

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Update: Actually, while BMP is indeed an abbreviation for "bitmap", it is not true that every bit in a BMP file is mapped in all cases. BMP files come in a variety of "flavors", but in general they can be broken down into "compressed" and "uncompressed". In the uncompressed variant of BMP files, it is correct that each bit is indeed "mapped" and as such the files tend to be larger than many other common image file formats. However, most BMP files that are in circulation or created by applications such as MS Paint are compressed BMP files. BMP files use a type of compression called "run length encoding", or RLE. Run length encoding will basically identify strings of adjacent pixels that are the same color value, and use a shorthand to indicate how many of that color. For example, imagine that the symbol "*" represents a certain shade of blue, and all other punctuation marks represent various other colors. Imagine, too, that there is a long horizontal line of blue pixel (a line) within a picture, and surrounded by various other colors. The RLE version of that might look something like this:

^2$1#1%1^2&1*240.1?1.1?.>1

The pattern in this case (just a theoretical example of how RLE encoding works) is [PIXELCOLOR][REPETITON]. You will notice two things - there are two entries for every pixel reference (this can cause a RLE encoded BMP file to be LARGER than the original file -- if there are a whole bunch of 1-2 pixel areas and not many areas in the image that are solid colors; secondly, this "bloat" is significantly counteracted when the "*240" is encountered, since the original (uncompressed) would have looked like 240 asterisks one after the other.

So, certain images compress better than others, and certain compression types are more suitable for certain image types. RLE is indeed one of the lossless types of compression. Lossless compression typically results in poorer compression ratios, but once decompressed, since none of the original image information has been discarded ("lost"), the decompressed version of the file will look exactly like the original.

JPEG, which is an acronym for the Joint Photographic Experts Group which developed the algorithms behind this popular compression, works better on pictures than on images with large areas of identically colored pixels. JPEG is a lossy compression, meaning that each time the image is compressed with this format, certain bits of information are "approximated" to improve the compression ratio; thus, when the file is decompressed for viewing, there are changes to the image quality. JPEG compression can be adjusted to provide better image quality by sacrificing some of the compression, or can be adjusted to be more highly compressed but with a sacrifice of image quality. For most of the images on the in internet, a balance is struck between good visual quality and good compression. However, since photographs are very common on the web, JPEG is perhaps the most popular format to be used online. JPEGs can provide a great compromise between acceptable image degradation and file size. However, since the compression algorithms have been specifically designed to work with the unique data that is seen insde a photograph, JPEG will usually wind up as a smaller file than BMP. However, if you convert an image that is only made from a small number of distinct colors, and those colors are mainly ground together in areas of the image, then a BMP file format might actually result in a smaller file.

So, if you are trying to decide which format you want to use, you have to decide whether a certain degree of image degradation is acceptable or not, and you should test while retaining copies of the original files (just in case). Generally, for web pages and items that will be displayed from within a web browser, you want to stay away from BMP, because it is not supported by all Web Browsers (MSIE supports it, however). If you need the page background to show through the "negative space" of your image, and not be blocked out as the background color of the image, then you will do better abandoning JPEG and BMP entirely, and using either GIF or PNG and taking advantage of these file formats' (some variants') inherent support for transparency and/or an "alpha channel."

Answer 2

because they have hundreds of thousands of pixels and each colour square is a pixel