tif file size 8 / 16 bit per channel

[RedRebel]

This is something I don't understand.

I scan images using silverfast at 2400 dpi and 48 bit color deptht. This results in a ~40mb tif file.

After opening this file in Photoshop I do some color correction and set the image from 16bit per channel to 8bit per channel. I save the tif file (as a copy) but then the file size increases to over 60mb?!? while I would have expected about 20mb.... 20MB is the size I get when I scan at 24 bit, which is stored at 8 bit per channel.

[Jonathan Wienke]

There's compressed TIFF and uncompressed TIFF, and TIFF can be 8 or 16 bit. PSD files are uncompressed. If you open a 16-bit compressed TIFF and save as PSD, the file will be larger, and will be 16-bit unless you explicitly convert to 8-bit.

[jjlphoto]

Are you saving any layers or alpha channels (selections)?

[francois]

René,
Things I would check:
- TIFF compression, although the size differences you are seeing seem too large to be linked to compression scheme alone.
- Alpha channels and layers.

[RedRebel]

Ok thanks for your comments, I have found the cause.

The *unexpected* large file size is caused by the layers I use for adjusting the colors. I use the methods descibed in the book "Photoshop for digital photographers". There are three layers used, one for the blackpoint, one for the whitepoint and one for neutral grey. Then I use "Curves" to adjust the colors.

When I delete these layers after color correction, the file size is about 40mb for 16bit and 20mb for 8 bit data, which is the expected file size.

Is it common to use any kind of compression when saving a tif file? I notice when I use LZW the file size is only reduced when saving as 8 bit per channel. When saving at 16 bit using LZW compression the file size becomes larger...