In article
<(E-Mail Removed)>,
Dances With Crows <(E-Mail Removed)> wrote:

> > send a FAX, the vertical and horizontal resolutions are different; FAX
> > machines use pixels that are not square.
>
> TIFF has supported having different horizontal and vertical resolutions
> since the format started up; this is not a fax-specific thing. Not many
> people use this TIFF capability, and some programs will barf if they
> read different values for TIFFTAG_XRESOLUTION and TIFFTAG_YRESOLUTION,
> but it's in the TIFF spec.

I certainly never intended to imply otherwise.

FAX machines use non-square pixels; TIFF also supports non-square pixels
as well. For the most part, if a person is scanning a file using a
consumer flatbed scanner, the only application that would likely require
non-square pixels would be preparing the document for faxing.

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On 01 Jun 2006, Dances With Crows<(E-Mail Removed)>
wrote:

>>> am also asked to fill in the dpi value horizontally and
>>> vertically.
>> Group 4 compression is the compression used by FAX machines.
>
> Fax machines use Group3, not Group4. Group3 is less efficient than
> Group4.
>
>> send a FAX, the vertical and horizontal resolutions are different;
>> FAX machines use pixels that are not square.
>
> TIFF has supported having different horizontal and vertical
> resolutions since the format started up; this is not a fax-specific
> thing. Not many people use this TIFF capability, and some programs
> will barf if they read different values for TIFFTAG_XRESOLUTION and
> TIFFTAG_YRESOLUTION, but it's in the TIFF spec.
>
>> then send FAXes. Since that's not what you're doing, there's no
>> reason to use CCITT Group 3 or Group 4 compression (which really
>> only works well on simple bitmaps anyway).
>
> Group4 is A) lossless B) more efficient than any other compression
> method for bilevel data. These qualities make Group4 an excellent
> choice for storing black-and-white images. Zak was scanning
> documents that consisted mostly of text, which is typically very
> high-contrast and works really well in black-and-white. So every
> page with just text (no graphics) on it could easily be turned into
> a Group4 TIFF with no loss of data. HTH,

I have hit a bit of a problem which I can solve only by using TIFF group
3.

The problem is that if I scan to TIFF group 4 and then edit in PSP, then
i find that the saved TIFF file is about 5 or 6 times the size of the
TIFF file before editing. This creates a horrible PDF with fuzzy edges.
Turns out that PSP was saving in LZW. However my PSP is ver9 and it
does not offer an option for TIFF group 4.

So I choose group 3 and I get a reasonably sized TIFF from PSP which
converts nicely into a PDF.

Can't work out why PSP does not offer Group 4.

PhotoShop is not much better and it seems, to me anyhow, to offer even
fewer compression options when saving to TIFF.

On 02 Jun 2006, Zak<(E-Mail Removed)> wrote:

>>> Group 4 compression is the compression used by FAX machines.
>>
>> Fax machines use Group3, not Group4. Group3 is less efficient
>> than Group4.
>>
>>> send a FAX, the vertical and horizontal resolutions are
>>> different; FAX machines use pixels that are not square.
>>
>> TIFF has supported having different horizontal and vertical
>> resolutions since the format started up; this is not a
>> fax-specific thing. Not many people use this TIFF capability, and
>> some programs will barf if they read different values for
>> TIFFTAG_XRESOLUTION and TIFFTAG_YRESOLUTION, but it's in the TIFF
>> spec.
>>
>>> then send FAXes. Since that's not what you're doing, there's no
>>> reason to use CCITT Group 3 or Group 4 compression (which really
>>> only works well on simple bitmaps anyway).
>>
>> Group4 is A) lossless B) more efficient than any other compression
>> method for bilevel data. These qualities make Group4 an excellent
>> choice for storing black-and-white images. Zak was scanning
>> documents that consisted mostly of text, which is typically very
>> high-contrast and works really well in black-and-white. So every
>> page with just text (no graphics) on it could easily be turned
>> into a Group4 TIFF with no loss of data. HTH,
>
> I have hit a bit of a problem which I can solve only by using TIFF
> group 3.
>
> The problem is that if I scan to TIFF group 4 and then edit in PSP,
> then i find that the saved TIFF file is about 5 or 6 times the size
> of the TIFF file before editing. This creates a horrible PDF with
> fuzzy edges. Turns out that PSP was saving in LZW. However my PSP
> is ver9 and it does not offer an option for TIFF group 4.
>
> So I choose group 3 and I get a reasonably sized TIFF from PSP
> which converts nicely into a PDF.
>
> Can't work out why PSP does not offer Group 4.
>
> PhotoShop is not much better and it seems, to me anyhow, to offer
> even fewer compression options when saving to TIFF.

Hmm. I am not sure my experiments have been as good as they ought to
have as Foxit and Adobe Reader seemed to get launched and I don't
recall which one was used when.