Best Format After Scan

[Jim]

There are times that I will scan something for editing later... what are
the best three formats to save the scan file as ie: RAW, TIFF and/or
some other? What are the pros/cons of each of your choices?

Probably a basic question for most of you but I'm still trying to
establish relationships between different formats. I truly appreciate
any comments you "scanners" might have to help me sort things out... Jim

 

[Brendan R. Wehrung]

There are times that I will scan something for editing later... what are
the best three formats to save the scan file as ie: RAW, TIFF and/or
some other? What are the pros/cons of each of your choices?

Probably a basic question for most of you but I'm still trying to
establish relationships between different formats. I truly appreciate
any comments you "scanners" might have to help me sort things out... Jim

I always save anything important as an uncompressed TIFF. It may take a
lot of disc space, but you can archive them to CD (burning two on
different brands of media).

Brendan

 

[Bucky]

There are times that I will scan something for editing later... what are
the best three formats to save the scan file as ie: RAW, TIFF and/or
some other? What are the pros/cons of each of your choices?

Depends what you're scanning. If these are photo quality images, then
probably TIFF since it is lossless.

 

[Bruce bowman]

There are times that I will scan something for editing later... what are
the best three formats to save the scan file as ie: RAW, TIFF and/or
some other? What are the pros/cons of each of your choices?

Probably a basic question for most of you but I'm still trying to
establish relationships between different formats. I truly appreciate
any comments you "scanners" might have to help me sort things out... Jim

I save my scans as TIFF files - I scan 35mm slides at 3600 dpi, so that
if they would later be printed at a 6" width - that would provide 600
dpi (3600/6" = 600 dpi). Scans at this resolution are about 45 - 49 MB,
but I process them with PaintShop Pro and reduce the number of colours
to 64,000 from 16M - this reduces file size to approx 10 - 15 MB, a
manageable size for storing on DVDs. The human eye can not tell the
difference between 64,000 colours & 16 M - saves a lot of storage space.

 

[Wayne]

The human eye can not tell the
difference between 64,000 colours & 16 M - saves a lot of storage space.

Ouch. Maybe not, color accuracy is not very good anyway, so the colors
probably are close enough unless matching paint samples. But 64K colors is
only 5 bits, or only 32 possible values of each primary color like red or
blue, so you very likely may see banding in wide gradients, such as skies.

In spite of the natural 16 bit native word size of our computers, it was
considered pretty important to change our video cards from 16 bits to 24
bits way back when, at least ten years ago (early iron age in computer
years). That was very near the beginning of computer photos.

The 16 bit color was 64K colors, with 5 bits of red, 5 bits of blue, and 6
bits of green. Only 32 colors from 5 bits was found insufficient.
The 64K color setting is retained only as an oddity from the past.
It seems a real waste of good images to me.

24 bit color is 8 bits of each, or 256 possible values of each primary.
You have to really go some to see banding in gradients now, but it is not
impossible.

 

[David J. Littleboy]

Ouch. Maybe not, color accuracy is not very good anyway, so the colors
probably are close enough unless matching paint samples. But 64K colors is
only 5 bits, or only 32 possible values of each primary color like red or
blue, so you very likely may see banding in wide gradients, such as skies.

Really. Pretty funny to be afraid of jpeg yet throw away that much
information.

IMHO, high-res scans have enough noise and softness in them that tiff is
simply unjustified. (Max quality jpeg is quite close to lossless compress as
long as it doesn't do chroma subsampling, and thus perfectly adequate for
3600 or 4000 ppi scanned images. The simple reality check here is that 3600
ppi corresponds to a 12x enlargement from film and at 12x, the next film
size up (at a lower enlargement) looks a lot better.)

But that treads on a lot of peoples' religious sensibilities.

David J. Littleboy
Tokyo, Japan

 

[Wayne]

Really. Pretty funny to be afraid of jpeg yet throw away that much
information.

Yeah, the highest quality JPG is a smaller file, yet better image, than only
64K colors.

Bruce, I assumed 16 bit color, and turns out there are some ifs and buts, but
the result is exactly the same. I see now that PSP has a 64K/24 bit option,
so it is not a 16 bit file. It is 16 bit color however, because this PSP
algorithm is 5 bits of red and blue and 6 bits of green. If you look at this
64K color image in Adobe Elements or Photoshop Levels, it is extremely
posterized, enough so that you can simply count the colors of red, and green,
and blue... only 32 values of red or blue, and 64 values of green are
present, all equally spaced into posterized picket fences or pocket combs.
That is 16 bit color, but in a 24 bit file.

But 24 bits is still three bytes per pixel, so it cannot eliminate any RGB
bytes. Therefore any size reduction effect must be only due to compression of
the fewer number of possible values.

So, you get all of the disadvantage of the posterization, without actually
saving on the 24 bit RGB bytes, except that higher compression is possible on
the fewer number of colors (so the file is smaller).

I tried a test image, about 5100x3400 pixels, which should compare to your
3600 dpi image. Mine was almost entirely green (foliage), but with 1.95
million colors originally, and I only got about 21K colors with the 64K color
option.

13,549,822 D.jpg Maximum quality, original, PSP compression level 1.
24,369,324 D64lzw.tif LZW compression - 64K color file.
32,509,794 D.png PNG compression - original image
40,453,426 Dlzw.tif LZW compression - original image
51,887,608 D.tif No compression - original image
51,887,608 D64.tif No compression - 64K color file.

The uncompressed 24 bit TIF files are obviously the same file size
(has to be ... 3 bytes RGB per pixel for 24 bit color)

The fewer 64K color values do much compress better with LZW than the greater
number of colors. That is very reasonable, and is how compression works.

But the maximum quality JPG is even smaller (PSP compression level 1 at
extreme left), and surely a much better image. This JPG retained 695K of the
1.95 million colors, and the maximum JPG file is only about half the size of
the 64K 24 bit LZW TIF file, yet it does still have 24 bit values and 695K
colors, and no posterization.

If you must have a small file, I'd bet on this JPG in any case. I would
first do all work on the image as a TIF file, and finish it completely, and
then save only the one time as JPG for archiving it.

 

[David J. Littleboy]

If you must have a small file, I'd bet on this JPG in any case. I would
first do all work on the image as a TIF file, and finish it completely,
and
then save only the one time as JPG for archiving it.

Agreed. I scan 4000 ppi at 16 bits, correct black and white points, adjust
colors and contrast fairly closely, and save as an 8-bit jpeg (not that one
has a choice about 8-bit with jpeg.)

Another thing is that you can convert to 16-bit before editing an 8-bit
file. That prevents errors from accumulating during the edit.

David J. Littleboy
Tokyo, Japan

 

[Jim]

Thanks for comments regarding best format to save a scan as when future
editing is required. Guess TIFF is the preferred format. I would have
thought RAW would have been mentioned as well.

My usage is very little photo work... mostly graphics/text that I want
to save until I can get back to edit for archiving. Any other lossless
formats that do not have as much overhead as TIFF?

Also appreciate the discussion leading up to JPG (max one time save) for
archiving. By accident... that is what I usually save final edited file
as... Jim

 

[Wayne]

Thanks for comments regarding best format to save a scan as when future
editing is required. Guess TIFF is the preferred format. I would have
thought RAW would have been mentioned as well.

My usage is very little photo work... mostly graphics/text that I want
to save until I can get back to edit for archiving. Any other lossless
formats that do not have as much overhead as TIFF?

Also appreciate the discussion leading up to JPG (max one time save) for
archiving. By accident... that is what I usually save final edited file
as... Jim

Jim, I dont know what you are scanning, but JPG is routinely NOT the best
choice for graphics/text. JPG is for photos (continuous tone), assuming
file size must be small.

As to image size, 24 bit color is 3 bytes per pixel. 8x10 inches at 300
dpi is 2400x3000 pixels, and 3 bytes per pixel is 2400x3000x3 = 21.6
million bytes. Doesnt matter what it is, if that is the image size, then
that is simply the size of the data. Grayscale is 1 byte per pixel.

File compression techniques can make it smaller in the file, but when you
open the file, it is 21.6 million bytes again in memory (assuming the same
color example). JPG is a very efficient file compression, but JPG does
this be being lossy, meaning you dont get back exactly what you thought
you wrote. JPG causes artifacts in the image, which always seem
particulary bad in text and graphics. High Quality JPG can be pretty
good, but then it does not compress as much, and then the file size can be
quite prohibitive if 100 pages of document.

Text:

But text is (as a rule) only two colors, black ink on white paper, which
is really line art scan mode. Line art data is 1 bit, or 1/8 byte per
pixel. You cannot put line art into JPG (it must convert it to grayscale).
But if in a TIF file with compression, then line art is maybe only 100K to
150K bytes per full page. TIF compressions like LZW or G3 are NOT lossy.

But if scanned as color and saved as JPG, not only will the color file be
at least 1/2 megabyte per page (assuming barely bearable quality), but the
JPG quality will be awful if that small. Those fuzzy shadows all around
each text character are JPG artifacts. The more you compress it, the worst
it is. However, line art in a TIF file can be very clear, and 300 dpi line
art will print well. 600 dpi line art (4x more pixels) will print serious
work better, important for production work, but 600 dpi can be overkill
for lesser work. 200 dpi is good fax grade.

Graphics:

Color graphics (except for gradients) are typically only a few colors of
ink, say less than 16 colors of ink. So instead of JPG, you can change
the graphics image to Indexed Color of maybe 16 colors (4 bits) which will
dramatically reduce the data size way below 24 bits per pixel. TIF with
compression will be VERY clear for this. Speaking of graphics, this is
totally unsuitable for photos.

This cleans up scanned graphics too, because graphic colors are typically
solid colors, that is, the blue is usually only one shade of blue ink in
the printing press, but it tends to come out as several blue shades in a
scan. Indexed color of limited color count will put it back into one shade
of pure blue (like cartoon skies - all one shade of blue). This 16 color
indexed color image in a TIF file with LZW compression will be a
dramatically smaller file than JPG can ever be, and will be much more
clear too (more pure colors, and no JPG artifacts).

Too much too soon here perhaps, but you might try it once to see if it is
suitable for your use.

 

[Raphael Bustin]

Thanks for comments regarding best format to save a scan as when future
editing is required. Guess TIFF is the preferred format. I would have
thought RAW would have been mentioned as well.

AFAIK, no format is ever converted *to* RAW. If you captured
the image in RAW, that's one thing, and saving (archiving) the
RAW makes some sense in that case.

Converting *to* RAW is somewhat nonsensical. Besides
which, "RAW" isn't the least bit universal. Every vendor's
RAW format is different.

If you archive in RAW, you are relying on the continued
existence of a RAW decoder for your particular RAW format.

My usage is very little photo work... mostly graphics/text that I want
to save until I can get back to edit for archiving. Any other lossless
formats that do not have as much overhead as TIFF?

PNG is lossless. It's a bit less "efficient" than best-quality JPG,
but more efficient than LZW. PNG can also store 16/48 bit images.

The only possible issue with PNG is that it's a relatively new
format, so it won't be as widely supported as TIF or JPG.

TIF is by far the best-supported image format, and with the
most options. Eg., it handles alpha channels, layers, embedded
profiles, etc.

Also appreciate the discussion leading up to JPG (max one time save) for
archiving. By accident... that is what I usually save final edited file
as... Jim

JPG is fine as an archival format for images in their final state.
It's not intended for works-in-progress.


rafe b
www.terrapinphoto.com

 

[Jim]

(e-mail address removed) says...


Jim, I dont know what you are scanning, but JPG is routinely NOT the best
choice for graphics/text. JPG is for photos (continuous tone), assuming
file size must be small.
--snip--

Too much too soon here perhaps, but you might try it once to see if it is
suitable for your use.

Wayne, you are right... too much too soon. It will take me a little
while to digest all of the info.

Most of my scanning consists of business letters, forms, invoices and a
little photo scanning. The straight black on white is no problem but I
usually documents with color logos or some non-black text in RGB. For
simplicity, I've found that GraphicConverter or VueScan work better for
this type of scan... Photoshop is just too complex for non-photo scans.

My initial post was regarding intermediate storage until I can edit and
archive... sometimes I will scan a 4-5 page document and leave it until
I get back to the office... or later. Then I will clean up the pages and
(try to) reduce the size for storage. It's important that the document
is stored so that if it needs to be printed again, that the printed copy
is acceptable.

So... now that JPG is not a good choice, what do you suggest?.. Jim

 

[Jim]

AFAIK, no format is ever converted *to* RAW. If you captured
the image in RAW, that's one thing, and saving (archiving) the
RAW makes some sense in that case.

Converting *to* RAW is somewhat nonsensical. Besides
which, "RAW" isn't the least bit universal. Every vendor's
RAW format is different.

If you archive in RAW, you are relying on the continued
existence of a RAW decoder for your particular RAW format.

I presume that RAW immediately after the scan is OK... but not as a
conversion.

PNG is lossless. It's a bit less "efficient" than best-quality JPG,
but more efficient than LZW. PNG can also store 16/48 bit images.

The only possible issue with PNG is that it's a relatively new
format, so it won't be as widely supported as TIF or JPG.

but for non-photo scans, I presume this would be OK... right?

TIF is by far the best-supported image format, and with the
most options. Eg., it handles alpha channels, layers, embedded
profiles, etc.



JPG is fine as an archival format for images in their final state.
It's not intended for works-in-progress.

understood. Thanks... Jim

 

[Wayne]

Most of my scanning consists of business letters, forms, invoices and a
little photo scanning. The straight black on white is no problem but I
usually documents with color logos or some non-black text in RGB. For
simplicity, I've found that GraphicConverter or VueScan work better for
this type of scan... Photoshop is just too complex for non-photo scans.

But Photoshop does have some great tools for non-photo images too.

There are never any absolute answers... much depends on situations, purposes,
and of course preferences. We dont all see the same answer.

For printing black text, line art scan mode is really hard to beat however.
Vuescan calls it "1 bit B&W" under Bits Per Pixel. Some scanner software
offer a Threshold control to improve line art - see
http://www.scantips.com/basics04.html for the idea. I am not aware that
VueScan offers Threshold, but Photoshop offers menu Image - Adjustments -
Threshold that does the same thing after a grayscale scan. Elements does
this too. I prefer doing it in the scanner software however, not an extra
step then -- you see effect in the preview. Threshhold is an easy important
skill for line art. Try it once, and you will get it. Good clear laser print
doesnt really need it, default 128 is usually fine. For magazine or newspaper
scans, lowering threshold, maybe around 90, is often very good to thin and
clean the characters. For too-light text, raising threshold a little is often
very good. You look at results of course to decide.

For color logos, you can 1) disregard the color, same for example as if on a
copy machine, which looking like a copy seems OK to me for most records, or
2) you can scan in color mode to retain the color if it is important enough
to pay that size price. But then (graphics), most of the time, Indexed color
(16 colors) should be best for that (clear and small file). See
http://www.scantips.com/palettes.html about Indexed Color. You would convert
to Indexed Color mode after the RBG scan - in Photoshop at menu Image - Mode
- Indexed Color, and then one of the Local (Perceptive or Adaptive) palettes,
16 colors, and Dither: None. Smaller, and compresses really well (TIF and
LZW). Try it once, and you will get it.

My initial post was regarding intermediate storage until I can edit and
archive... sometimes I will scan a 4-5 page document and leave it until
I get back to the office... or later. Then I will clean up the pages and
(try to) reduce the size for storage. It's important that the document
is stored so that if it needs to be printed again, that the printed copy
is acceptable.

So... now that JPG is not a good choice, what do you suggest?.. Jim

TIF is really hard to beat anytime, for intermediate or final results, maybe
more important for intermediate. File compression (like TIF LZW) is
particularly effective for line art or Indexed color (small files), and less
efficient for grayscale or color (not reduced in size as drastically). PNG
is also good and fine, equal with TIF. PNG does an automatic lossless
compression a bit smaller than TIF LZW, but it is a bit slower too. Your
preference. Either one will handle line art, Indexed Color, Grayscale, RGB,
etc, etc.

 

[Jim]

But Photoshop does have some great tools for non-photo images too.

There are never any absolute answers... much depends on situations, purposes,
and of course preferences. We dont all see the same answer.

For printing black text, line art scan mode is really hard to beat however.
Vuescan calls it "1 bit B&W" under Bits Per Pixel. Some scanner software
offer a Threshold control to improve line art - see
http://www.scantips.com/basics04.html for the idea. I am not aware that
VueScan offers Threshold, but Photoshop offers menu Image - Adjustments -
Threshold that does the same thing after a grayscale scan. Elements does
this too. I prefer doing it in the scanner software however, not an extra
step then -- you see effect in the preview. Threshhold is an easy important
skill for line art. Try it once, and you will get it. Good clear laser print
doesnt really need it, default 128 is usually fine. For magazine or newspaper
scans, lowering threshold, maybe around 90, is often very good to thin and
clean the characters. For too-light text, raising threshold a little is often
very good. You look at results of course to decide.

For color logos, you can 1) disregard the color, same for example as if on a
copy machine, which looking like a copy seems OK to me for most records, or
2) you can scan in color mode to retain the color if it is important enough
to pay that size price. But then (graphics), most of the time, Indexed color
(16 colors) should be best for that (clear and small file). See
http://www.scantips.com/palettes.html about Indexed Color. You would convert
to Indexed Color mode after the RBG scan - in Photoshop at menu Image - Mode
- Indexed Color, and then one of the Local (Perceptive or Adaptive) palettes,
16 colors, and Dither: None. Smaller, and compresses really well (TIF and
LZW). Try it once, and you will get it.



TIF is really hard to beat anytime, for intermediate or final results, maybe
more important for intermediate. File compression (like TIF LZW) is
particularly effective for line art or Indexed color (small files), and less
efficient for grayscale or color (not reduced in size as drastically). PNG
is also good and fine, equal with TIF. PNG does an automatic lossless
compression a bit smaller than TIF LZW, but it is a bit slower too. Your
preference. Either one will handle line art, Indexed Color, Grayscale, RGB,
etc, etc.

Wayne... thanks. This makes a lot more sense. I will give it a go if I
run into any problems, will post specifically.

I have read through ScanTips a few times... mostly when I was using
MicroTek scanners as they recommended it. Dumped them due to never being
able to get a white background on a business letter when the scanner
went bad... their driver, was and probably still is great for photos but
not business documents. May be time for a review. Thanks again... Jim

 

[Wayne]

Wayne... thanks. This makes a lot more sense. I will give it a go if I
run into any problems, will post specifically.

I have read through ScanTips a few times... mostly when I was using
MicroTek scanners as they recommended it. Dumped them due to never being
able to get a white background on a business letter when the scanner
went bad... their driver, was and probably still is great for photos but
not business documents. May be time for a review. Thanks again... Jim

To each his own I guess, but I do love my Microtek flatbeds and Scanwizard,
for both photos and documents. I use VueScan with film scanners, for its easy
good color from film. BTW (since you mentioned RAW), RAW would not be
appropriate for documents (1000% overkill). RAW is only for film, but I have
no use for RAW then, a 16 bit TIF file does all I need. However RAW from
cameras is a different story (both for the great tools available, and as a way
to skip JPG).

Frankly, I dont have that problem with white backgrounds, but if your document
background doesnt come out quite white on any scanner, lowering the histogram
White Point just a tad should fix it easily, same idea as for photos.
Even if the paper actually wasnt quite white either. Documents work the
same as photos, but documents will accept a lot more of it.

Of course, if the document were scanned in line art mode, then there is not
much question about background... line art can only be full white or full
black. The threshold control determines which side (white or black) of the
threshold the middle tones fall (by moving the threshold).

 

[Don]

Thanks for comments regarding best format to save a scan as when future
editing is required. Guess TIFF is the preferred format. I would have
thought RAW would have been mentioned as well.

In the context of scanners, RAW refers to what is done to the data
after the scan, not the file format this data is saved as. In theory,
you can save scanner RAW data in any (lossless) image format.

To make thing clearer, if you turn every image processing option in
your scanner software (curves, levels, etc) what you should be getting
is "raw" image data from the scanner. It's a bit more complicated than
that but that's the gist of it.

Now, having received this data you then save it in the format of your
choice. Since you went through all the trouble of getting this raw
data out it makes sense to use a graphics/image format which is
lossless so all that data is preserved.

Do note that in the context of *digicams* RAW means something
completely different. In a sense, the raw data from a digicam is lower
level than the raw data one gets from the scanner. Namely, the digicam
raw data doesn't even contain pixels but groups of pixels which are
then converted into a single pixel. That's because in a scanner the
three RGB colors overlap the same physical spot in the source object
being scanned. In a digicam, they are side-by-side (actually 2 green,
1 red and 1 blue) and they have to be "merged" and converted into a
single (spatial) pixel. Do note also that in case of digicams the RAW
format is usually closed and proprietary although there are moves to
come up with an open industry standard.

My usage is very little photo work... mostly graphics/text that I want
to save until I can get back to edit for archiving. Any other lossless
formats that do not have as much overhead as TIFF?

Actually, TIFF has very little overhead. Indeed, probably the least
overhead of all the other format. A bare bones RGB TIFF file only
needs about 160 bytes (that's BYTES!) of overhead per image!

Some graphics programs may go nuts and add tons of garbage but that's
the problem with those programs, not TIFF.

TIFF layout is also open so it's bound to be supported in the future
or, at the very least, there will be converters.

Don.

 

[Don]

Converting *to* RAW is somewhat nonsensical.

As well as impossible. Neither editing (as in scanner raw) nor Bayer
conversion (as in digicam raw) can be undone without major data loss.

If you archive in RAW, you are relying on the continued
existence of a RAW decoder for your particular RAW format.

That only applies to *proprietary* digicam RAW because there the data
state and file format are merged into one (for commercial reasons).

As explained in the message to Jim, there's a difference between *data
state* (raw) and *file format* (layout) where this data is saved.

In terms of scanners, that doesn't really apply because (other than
Nikon's feeble attempt with *scanner* NEF) the two are separate and
one could save scanner RAW in any file format. Of course, that doesn't
apply to Nikon's *digicam* NEF which is not only proprietary but
encrypted and whatnot...

Don.

 

[Jim]

To each his own I guess, but I do love my Microtek flatbeds and Scanwizard,
for both photos and documents. I use VueScan with film scanners, for its
easy
good color from film. BTW (since you mentioned RAW), RAW would not be
appropriate for documents (1000% overkill). RAW is only for film, but I have
no use for RAW then, a 16 bit TIF file does all I need. However RAW from
cameras is a different story (both for the great tools available, and as a
way
to skip JPG).

Frankly, I dont have that problem with white backgrounds, but if your
document
background doesnt come out quite white on any scanner, lowering the histogram
White Point just a tad should fix it easily, same idea as for photos.
Even if the paper actually wasnt quite white either. Documents work the
same as photos, but documents will accept a lot more of it.

Of course, if the document were scanned in line art mode, then there is not
much question about background... line art can only be full white or full
black. The threshold control determines which side (white or black) of the
threshold the middle tones fall (by moving the threshold).

I had no problem with the quality of the Microtek flatbed I bought
EXCEPT that within a short time... but after warranty expired, the
circuit board went bad leaving a vertical line the length of the scan.
By this time I was exasperated with ScanWizard. I could not scan our
business letterhead or invoice without the scan image having a blue
tint. Didn't matter what was tried... I even sent a letterhead to
Microtek support and let Natasha work with it without success... stating
that the logo on the letterhead (which is different shades of blue) was
not allowing ScanWizard to give a white background. I asked why the UMAX
scanner that I used to use produced a white background and perfect logo
in RGB. No answer... other than something about RGB and photos of which
I interpreted that the letterhead was too simple for ScanWizard.

Later I sent a scanned tiff to a different Microtek tech and after he
spent the weekend working with it, returned it to me saying that this
was the best that could be done in Photoshop. Blue tint was still
present.

Interestingly... the Epson scanner that I have used for the past couple
of years scans our letterheads and invoices perfectly.

I realize I could have scanned in line-art for archiving... but that was
not the scanning purpose nor the challenge... Jim

 

[Jim]

In the context of scanners, RAW refers to what is done to the data
after the scan, not the file format this data is saved as. In theory,
you can save scanner RAW data in any (lossless) image format.

To make thing clearer, if you turn every image processing option in
your scanner software (curves, levels, etc) what you should be getting
is "raw" image data from the scanner. It's a bit more complicated than
that but that's the gist of it.

Now, having received this data you then save it in the format of your
choice. Since you went through all the trouble of getting this raw
data out it makes sense to use a graphics/image format which is
lossless so all that data is preserved.

Do note that in the context of *digicams* RAW means something
completely different. In a sense, the raw data from a digicam is lower
level than the raw data one gets from the scanner. Namely, the digicam
raw data doesn't even contain pixels but groups of pixels which are
then converted into a single pixel. That's because in a scanner the
three RGB colors overlap the same physical spot in the source object
being scanned. In a digicam, they are side-by-side (actually 2 green,
1 red and 1 blue) and they have to be "merged" and converted into a
single (spatial) pixel. Do note also that in case of digicams the RAW
format is usually closed and proprietary although there are moves to
come up with an open industry standard.


Actually, TIFF has very little overhead. Indeed, probably the least
overhead of all the other format. A bare bones RGB TIFF file only
needs about 160 bytes (that's BYTES!) of overhead per image!

Some graphics programs may go nuts and add tons of garbage but that's
the problem with those programs, not TIFF.

TIFF layout is also open so it's bound to be supported in the future
or, at the very least, there will be converters.

Thanks for detail... you guys have convinced me that TIFF is the format
for my interim needs... Jim