Q-Factor

[Claude Sapp]

I read a bit about the Q-Factor setting in Silverfast here on the forums and in the manual, but can't quite get my head around it. Basically, what the heck does it do to the file?

If I scan at 48 bits with a resolution of 2400 and size it for 4x5 inches, I expect a file size of ~659GB. Setting a Q = 1 and (screen is then 2400) I get this file size, but if you change the value the file size changes, so what is the software doing to the data?

[darr]

According to the Silverfast Q & A:


Q: The SilverFast user interface has an entry field for Q-factor. What does the Q-factor actually do?

A: In SilverFast you have the possiblility to determine the scan resolution by setting the Quality Factor (Q-Factor). This Q-Factor indicates the relation between line screen resolution (lpi) and scan reslolution (ppi resp. dpi).

A Q-Factor of 1.5 means that the scan resolution is 1.5 times larger than the line screen resolution.

How to calculate the maximum scan resolution with no information loss.?
desired output sreen x quality factor x scaling factor = scan resolution

Example
scanning a photo that is destined to be printed at a print pattern of 175lpi, and the photo is scanned 1:1 size (not enlarged or downscaled) this is your calculation:

175lpi x 1.5 x scaling factor (1:1 = output scaling 100% = 1) = ? 175lpi x 1.5 x 1 = 262,5dpi

SilverFast runds it off to 262dpi

Hope this is helpful. :)

[Claude Sapp]

OK, I know, I read that, but that still does not tell me what the software is doing.

if Q=1
screen = 2400
resolution = 2400 @ 48bits
image = 4x5 in
file size = 659MB

if Q = 1.5
screen = 1600
resolution = 2400 @ 48 bits
image = 4x5 in
file size = 659MB

What is different about these scans? Seems like I am still getting 48 bits of data at 2400dpi in each case, so what does Q-Factor and screen do?

[darr]

Claude,

Read this posting for more explanation since Q factor comes from the CMYK press world (http://forum.silverfast.com/q-factor-among-other-things-t355.html).