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PGY 4440C PHOTO COMPUTER IMAGING
Loss or no loss, that is the question
If you take a look at the manual or the menu of a digital
camera or an image editing program, you'll find terms like Raw, TIFF and
JPEG. This already gives some indication of the various methods used to
save data from a digital camera on a storage medium.
Generally speaking, a distinction can be made between methods that compress
without loss (lossless), and thus do not eliminate any image details,
and those that reduce the file size at the expense of image information
(lossy).
Lossless methods
Lossless compression is very easy to define:
The original image can be restored in absolutely identical form at any time – after decompression, every pixel has exactly the values it had before compression.
The proprietary formats of image editing programs – such as the *.PSD format in Adobe Photoshop – are often equipped with lossless compression algorithms. There are, however, also other methods.
LZW
The so-called TIFF format (Tagged Image File Format) uses a lossless compression method known as the Lemple-Zif-Welch (LZW) method. However, this version, which good image editing programs offer as an option when saving, is only capable of significantly reducing the file size of images containing a relatively large proportion of plain-colored areas. With our photo of the fuchsia flowers, it only reduces the memory space requirement by 3 percent.
Picmaster is one example of a shareware program that offers LZW compression for the TIFF format.
As promised by the compression method, a comparison of the uncompressed and LZW-compressed image detail (which is again shown here in PNG format after lossless compression) shows no difference in quality.
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