Image Compression and File Format

The picture quality in digital photography depends a great deal on file format and compression rates. These settings determine the size of the file. There are images without compression (TIF), with lossless compression RAW) and lossy compression (JPEG).


Uncompressed file formats

  • In uncompressed file formats each pixel’s brightness and colour information (TIF) is saved. This results in very large amounts of data. This format is ideal for lossless editing and re-saving.

Compressed file formats

  • Lossless compression (RAW): the data is processed by compression algorithms which reduces data storage space. When opened, the quality of the image file remains the same as the original. The RAW format should be changed to a Tiff or a JPG before it is passed on for e.g. further processing in the photo laboratory as otherwise the receiver may not be able to open the file.
  • Lossy compression (JPG): software checks for areas where all the pixels are similar in colour and brightness. Then, the first pixel’s full information is stored and it registers that the other pixels are practically identical. Depending on the compression rate, the pixels that differ increasingly in colour and brightness from the first pixel are grouped together. This results some detail lose when storing the file.

JPG format users should already think about their colour space in advance. For this purpose, sRGB and AdobeRGB are availabale on most cameras. The sRGB colour space is more restricted than the AdobeRGB colour space. For displaying images on the internet, the sRGB is a good choice. Even if no further editing is involved, this colour profile is optimal. For further image editing and/or prepress select the larger colour space AdobeRGB. Images captured in RAW mode can be converted into a different format. You can find more information about calibration in the respective article (still in the process).

Further, very good information, can be found under Wikipedia.org.

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