how to choose scan type?

[jlumbtx]

I have SilverFast SE version 8. On one of the menus is Scan Type, allowing me to chose 48>25 Bit Colour or 16>8 Bit Grayscale or 1 Bit Line Art or 48 Bit Colour or etc. etc.....
I am unable to find any explanation of why I should choose 48>24 bit color or 48 bit color when scanning my slides. There must be something in one of the instruction sheets
but I can't find it. What is each of these setting on this menu good for?

John in Houston

[LSI_Ketelhohn]

Dear John,

48bit and 16bit grayscale are used fro professional post-processing of images.
These images are best for processing in professional software like SilverFast HDR (Studio) and Photoshop.
They can not be opened by many other applications and are not suited for "common use".
These files are also very large as they can not be compressed very much and need to be stored in Tiff, JP2 or PSD formats.

For most other cases the 48->24 or 16->8 grayscale outputs are the right choice.
This is the bit depth most files use.
Such data can be stored in any file type available.

The 1bit output is for scanning line art only.

kind regards,
Arne Ketelhohn.

[jlumbtx]

Thank you.

[billhirst]

What does LaserSoft Imaging intend to convey by "48->24" bit?
I can see rationale for 48bit (3x16bit) and 24bit (3x8).
Having now read scores of forum posts (in the absence of a Silverfast technical manual in which I could look things up) I now realise the distictions of 48bitHDR and 64bitHDRi.
But the intended meaning of 48->24 bit remains elusive.
Do you just mean "as much information as the scanner can provide.... but don't kid yourslef you are getting 16 bit per channel - you'll be lucky to get 11 or 12 bits per channel!
Thanks for any illumination you can offer, Bill

[LSI_Ketelhohn]

Most current Scanners deliver data in 48bit (16bit per RGB channel) only a few very old devices deliver only 36bit (12 Bit per Channel).

The 48->24 Bit setting creates an output at 24Bit (8bit per RGB channel) which is the common format used in most images.
JPEG files also can only contain 24bit images and are only offered in this mode.
24Bit images are used for all common uses.

All the processing inside SilverFast uses the full 48 Bit information the scanner delivers.
Only the output at the end will be 24 Bit.


Kind regards,
Arne Ketelhohn

[billhirst]

Aha! Thank you Arne, that is now clear.

So as a user of Lasersoft Ai Studio 8, on Windows XP 32bit, with an Epson 4870 scanner. With IT8 colour management delivering a deltaE of ~0.7 for colour transparencies; It would make sense to use 48bit scanning, which allows me to use iSRD, and Multi-Exposure?

Am i right that it is impossible for me to activate Multi-Exposure when performing the IT8 calibration? Is this unnecessary because IT8 is all done at 48bit automatically?

Much appreciate your clarifications. Kind regards, Bill

[LSI_Ketelhohn]

Dear Bill,

If you plan to further process your images in an advanced imaging software like SilverFast HDR Studio or Photoshop?
Using 48bit would only benifit such a workflow, as these files can not be read by many applications.

For most other kinds of use t24 Bit images will be needed.

The IT8 calibration has nohing to do with Multi-Exposure.

kind regards,
Arne Ketelhohn.