Instruction manual

17
7. File Format
When your image file is, for example, a "16-bit TIFF" file this means that image
intensities are encoded with 16 bit numbers, giving 65,536 (2 to the power of 16)
possible different values for each pixel. In contrast, an 8-bit image file only stores
256 different values per pixel. The number of bits per pixel is also called the color
depth. The following table shows some examples.
color depth intensity levels example
1 bit
2
black and white FAX image
8 bit
256
GIF image
10 bit
1,024
TIFF image
12 bit
4,096
TIFF image
16 bit
65,536
TIFF image
Typical color depths
TIFF images can have different color depth, this is one of the reasons why TIFF is
widely used as standard image file format.
Generally, having more possible intensity values per pixel (higher color depth) is
needed for advanced analysis. The tradeoff is between higher accuracy and need for
more space to store the information: a 16 bit TIFF file is twice as large as the
equivalent 8-bit file, but results in 256 times more nuances in the image that can be
processed. Nonetheless, it has to be considerate that often image processing
programs are not able to deal with color depths greater than 8 bit.
Decreasing color depth in the scanned image file normally results in loss of accuracy.
It is not recommended to increase color depth after the scan is completed: if your
scanner produced only an 8-bit image you have at most 256 different intensity values
in the image. Converting the file to a 16-bit image will only give you at most 256 out
of 65,536 possible gray values.