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How to choose the right image file format for your needs.

BMP, GIF, PNG, JPG, what do all these things mean? Here is a brief guide about how to choose the format for your image files.

Your choice of file format really depends on how much detail and how many colors you want to lose. Lossy image file formats reduce the size of the image file by losing some detail or colors, hence the name!

In general WEB pages use lossy file formats, in order to reduce file size and thus speed up the display of pages.

BMP. BMP (BitMaP) files are the Windows "standard" image file format. I mean "standard" since 16 bit Windows 3.0. BMP image files are very bulky and unsophisticated. I cannot imagine any reason to store images in BMP format. It has lossy and lossless versions, but in both cases there are better alternatives.

GIF. Graphics Interface Format is a format with a limited amount of colors (in general a maximum of 256 colors per image) which has two advantages:

  • It is ideal for images with a few colors, flat cartoon like images for example. This is why ads on WEB pages use GIF. Small photographs (say 300 by 300 pixels max) can also look good in GIF format.
  • It is one of the few file formats which can contain animation. Again this is why ads on WEB pages use GIF.

The disadvantages of GIF are:

  • Lack of colors (only 256) makes it unsuitable as a storage format for large photograhs with many colors.
  • Even though the file size is smaller than BMP, it can sometimes be bigger than in JPG files.
  • Since it is a compressed file format you will almost certainly lose detail and colors if you use it for large photographs. By large photographs I mean the size of photos modern digital cameras produce, starting ay 1024 pixels wide.

PNG. The Portable Network Graphics format was designed to be a lossless format for use on the WEB (among other things). It does reduce the size of your files. However since it preserves all the detail and all the colors the size reduction is not as much as GIF or JPG. PNG is a good format for saving your images. Most modern browsers support PNG, you can see if yours does later in this article.

JPG. JPG stands for Joint Photographic Group, which is the name of the organization which created this format. JPG was designed for the storage of photographs and is in fact used in most digital cameras. It is lossy, so you do lose detail, but you can choose how much detail you lose.

In some paint programs you can set the JPG quality:

  • If you choose high quality then the JPG file will have all the details of the photograph, but the file size will be large.
  • If you choose medium quality you will have a very decent photograph with a reasonable file size.
  • If you select low quality then the file size will be small, but the image will appear blurry and blocky.

JPG is great for sending photographs via email, and for photographic images on the WEB.

Here are some examples in the various formats. You may not be able to see them all, it depends on your browser:



GIF with small photos works well. Size: 83 Kbytes.


PNG preserves all the detail and all the colors. Size: 212Kbytes


JPG at high quality works well. Size: 85Kbytes


JPG at medium quality works well. Size: 44Kbytes


JPG at low quality. Size: 5Kbytes

That last image really shows the problem with low quality JPG files. But look at the file size! Only 5Kbytes! Never mind the quality - feel the width!

You can see the problem with GIF files with large photographs in the next two examples. The first is a detail from a photo saved as PNG, fluffy clouds and nice shading. The second is the same detail after the image has been saved as a GIF file.

PNG or good quality JPG GIF

PNG and GIF details compared

See how GIF has run out of colors (it only has 256) when it tries to do the delicate shading of the sky.

Summing up:

  • Save your digital photos and original artwork as PNG files.
  • If you put photos in the WEB pages, or send them by email, use medium quality JPG.

MegaPixels and Inches explained

DPI explained

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