File Formats

VueScan reads raw sensor data from scanners and writes this data to a TIFF file for subsequent processing. The final cropped data can be stored in a TIFF file and/or a JPEG file. Index prints are always stored in a standard Windows BMP file.

The raw and cropped TIFF files can have 6 different formats, each with a different number of samples per pixel and bits per sample. A grayscale image has 1 sample per pixel, a normal color image has 3 samples per pixel (red, green, blue), and scans from a scanner with an infrared channel can have 4 samples per pixel (red, green, blue, infrared). VueScan internally keeps all samples in 16-bit linear format, even when a scanner only supports 10-bit samples, but to minimize the disk usage, various TIFF file formats are supported:

 1 bit B/W      1 bit   per pixel 1 sample  per pixel  1 bit  per sample
 8 bit Gray     1 byte  per pixel 1 sample  per pixel  8 bits per sample
16 bit Gray     2 bytes per pixel 1 sample  per pixel 16 bits per sample
24 bit RGB      3 bytes per pixel 3 samples per pixel  8 bits per sample
48 bit RGB      6 bytes per pixel 3 samples per pixel 16 bits per sample
64 bit RGBI     8 bytes per pixel 4 samples per pixel 16 bits per sample
16 bit Infrared 2 bytes per pixel 1 sample  per pixel 16 bits per sample

If you want to process the full bit depth of an image in Photoshop(TM), use the 48 bit RGB setting for the Crop TIFF file. Note that some other image editing tools cannot process 48 bit TIFF files; 24 bit is more widely compatible.

Note that the raw scan files are stored in linear format when using more than 8 bits per sample, and stored in gamma 2.2 format when using only 8 bits per sample. The saved TIFF files are always gamma corrected according to color space used (1.8 for Apple RGB, ColorMatch RGB, ProPhoto RGB and ECI RGB and 2.2 for all other color spaces). Note that the raw scan files stored in linear format will look dark when viewed. This is normal.

Note that both the scan TIFF file and the crop TIFF file can be compressed. VueScan uses CCITT Group-IV compression for 1-bit files, and LZW compression otherwise. This is a bit slower to write, but takes 40% less disk space on average. The size of the JPEG files can be controlled with the JPEG quality option, with useful values ranging from 75 (very compressed, medium quality) to 95 (not compressed very much, high quality).