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48 bit vs. 32 bit

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Anonymous
April 13, 2004 8:53:25 PM

Archived from groups: alt.comp.periphs.scanner (More info?)

Is there truly any noticeable difference between the 2 different color bits
when printing on a photo printer? both bits seem to represent millions of
colors. The only difference is in the file sizes. If one was scanning
slides/photos what would be the best choice....48 bit at a lower resolution
or 32 bit at higher resolution? any experienced opinions out there?

More about : bit bit

Anonymous
April 14, 2004 2:31:23 AM

Archived from groups: alt.comp.periphs.scanner (More info?)

In article <107orq77nujce4a@corp.supernews.com>, dgvxfcsrt@okghbvg.org
says...
>
>
>Is there truly any noticeable difference between the 2 different color bits
>when printing on a photo printer? both bits seem to represent millions of
>colors. The only difference is in the file sizes. If one was scanning
>slides/photos what would be the best choice....48 bit at a lower resolution
>or 32 bit at higher resolution? any experienced opinions out there?



Best case is no visible difference at all, because printers and video boards
only accept 8 bits per RGB channel, for a total of 24 bits. We cannot see
more than 24 bits on our hardware, because it cannot show it.

32 bits is for CMYK color images, four channels, but it is still 8 bits per
channel. You do NOT want CMYK mode for a photo printer (there can be rare
exceptions with special CMYK Postscript RIP drivers). Prepress screens are
of course the main exception, but consumer inkjets want 24 bit RGB images.

If you feed your inkjet more than 24 bit RGB images, the driver will first
convert to 24 bit RGB, and that conversion is probably a bad thing. You
should instead give it what it expects... 24 bit RGB.

Scanners do 36 bits or 42 bits or 48 bits (12, 14, or 16 bits per RGB
channel). The reason is for the extreme gamma adjustment they must do,
which shifts the tones drastically on a nonlinear curve, and the greater
precision allows that extreme shift to retain more unique tones, instead of
causing a picket fence look (gaps and clumping) in the data histogram. But
after tonal adjustments are complete, there is no reason to archive more
than 24 bit RGB. Our printer and video hardware cannot show more.

--
Wayne
http://www.scantips.com "A few scanning tips"
Anonymous
April 14, 2004 2:41:45 AM

Archived from groups: alt.comp.periphs.scanner (More info?)

Thanks for the info. For your info I have a HP Photosmart printer, it takes
2 colour cartridges, one is the typical tri-color the other is 3 "pastel"
colors. When I open up print dialogue it gives me the option of printing in
4800 dpi "optimized" I'm guessing that means the software will "pixelize"
the file to create a better photo. On another note, if my printer does take
2 cartridges with more than 3 colors does that affect the 24 bit limit you
mentioned?

I made a mistake in my earlier posting, my scanner offers 48 bit and 24 bit
(not 32)

I'm continuing to experiment, it seems that for scanning my 35mm slides I'm
tending to settle with 24 bit color @6400 resolution. Keeping in mind that
I'm creating a master digital archive for long term storage, and from that
master file I will create scaled down images for CD/DVD viewing on a screen
such as TV or monitor, However I want to have that digital archive available
to be able to create the most optimum prints for various selected images
that family members may request.

Am I on the right track here?

Much appreciate all your help,
Bob


"Wayne Fulton" <nospam@invalid.com> wrote in message
news:rIednTQO29QULeHdRVn-vg@august.net...
> In article <107orq77nujce4a@corp.supernews.com>, dgvxfcsrt@okghbvg.org
> says...
> >
> >
> >Is there truly any noticeable difference between the 2 different color
bits
> >when printing on a photo printer? both bits seem to represent millions of
> >colors. The only difference is in the file sizes. If one was scanning
> >slides/photos what would be the best choice....48 bit at a lower
resolution
> >or 32 bit at higher resolution? any experienced opinions out there?
>
>
>
> Best case is no visible difference at all, because printers and video
boards
> only accept 8 bits per RGB channel, for a total of 24 bits. We cannot see
> more than 24 bits on our hardware, because it cannot show it.
>
> 32 bits is for CMYK color images, four channels, but it is still 8 bits
per
> channel. You do NOT want CMYK mode for a photo printer (there can be rare
> exceptions with special CMYK Postscript RIP drivers). Prepress screens are
> of course the main exception, but consumer inkjets want 24 bit RGB images.
>
> If you feed your inkjet more than 24 bit RGB images, the driver will first
> convert to 24 bit RGB, and that conversion is probably a bad thing. You
> should instead give it what it expects... 24 bit RGB.
>
> Scanners do 36 bits or 42 bits or 48 bits (12, 14, or 16 bits per RGB
> channel). The reason is for the extreme gamma adjustment they must do,
> which shifts the tones drastically on a nonlinear curve, and the greater
> precision allows that extreme shift to retain more unique tones, instead
of
> causing a picket fence look (gaps and clumping) in the data histogram.
But
> after tonal adjustments are complete, there is no reason to archive more
> than 24 bit RGB. Our printer and video hardware cannot show more.
>
> --
> Wayne
> http://www.scantips.com "A few scanning tips"
>
Related resources
Anonymous
April 14, 2004 3:00:45 PM

Archived from groups: alt.comp.periphs.scanner (More info?)

In article <107pg7b55iqrm7c@corp.supernews.com>, dgvxfcsrt@okghbvg.org
says...
>
>
>
>
>Thanks for the info. For your info I have a HP Photosmart printer, it takes
>2 colour cartridges, one is the typical tri-color the other is 3 "pastel"
>colors. When I open up print dialogue it gives me the option of printing in
>4800 dpi "optimized" I'm guessing that means the software will "pixelize"
>the file to create a better photo. On another note, if my printer does take
>2 cartridges with more than 3 colors does that affect the 24 bit limit you
>mentioned?


There is a huge conceptual difference between the printers ink dot ratings
(like 4800 dpi), and the image's pixel resolution (like 300 dpi, but this dpi
term has a very different meaning).

The printers rating is about motor steps to position ink drop dots of 3 or 6
colors (about ink drops of 3 or 6 colors, not about pixels). This is a
Quality setting, not really a resolution setting. This number is NOT about
image pixels. The 6 colors vs 3 colors does not affect resolution, but 6 can
help to print photo quality better, so that the lighter ink dots are less
visible in the lighter colored areas.

The image resolution (like 300 dpi) is about pixels per inch (dpi or ppi are
interchangable in this use), where each pixel might be one of 16 million
colors. This is NOT at all the same thing as ink drop dots.

You want to select one of printers higher quality ratings to print photo
quality (as opposed to a low quality but fast draft mode setting), but you
scale images in the ball park of about 300 dpi (pixels per inch) for photo
quality. Maybe print 300 dpi images at 4800 dpi printer setting.

See http://www.scantips.com/basics3b.html for more about this difference.


>I made a mistake in my earlier posting, my scanner offers 48 bit and 24 bit
>(not 32)
>
>I'm continuing to experiment, it seems that for scanning my 35mm slides I'm
>tending to settle with 24 bit color @6400 resolution. Keeping in mind that
>I'm creating a master digital archive for long term storage, and from that
>master file I will create scaled down images for CD/DVD viewing on a screen
>such as TV or monitor, However I want to have that digital archive available
>to be able to create the most optimum prints for various selected images
>that family members may request.
>
>Am I on the right track here?

I seriously doubt you have a 6400 dpi scanner? But if somehow you do, then
there is a special time and place you might consider using it. The concept is
that the ratio of (scanning resolution / printing resolution) is the
enlargement factor. For example, scaling to (6400 dpi scan / 300 dpi print)
would give 6400/300 = 21.3X size enlargement, printing about 30x20 inches
from 35 mm film size. If that is the goal, and if you have a 6400 dpi
scanner, then that is the right plan (except that such large prints are not
normally printed at 300 dpi, because the requirements are so great, and
printers that size often cannot physically do 300 dpi).

More normally, we might scan 35 mm film at say 2700 dpi and print at 300 dpi,
for 2700/300 = 9x enlargment. 35 mm film is about 0.9x1.4 inches, so this 9x
is about 8x12 inches (about A4 size) from 35 mm film. This image size would
be about (8 inches x 300 dpi) x (12 inches x 300 dpi) = 2400x3600 pixels,
about 25 MB.

Again, the purpose dictates this. If you wish to print 8x12 inches, then this
is appropriate. If you won't print it 8x12 inches, then it is probably still
excessive for the purpose. When scanning prints, enlargement is less often
an issue, so we might scan at 300 dpi, print at 300 dpi, for 100% size (no
enlargement).

Some scanners can output 48 bits, but only a few photo editor programs can
accept 48 bits, and our printers and video want 24 bits too. I think you
probably want 24 bits. If you have a 16 bit program (like full Photoshop),
then some people do like to output 48 bits, correct the tone adjustments, and
then convert to 24 bits for printing or archiving.

The site below should be a big help to you getting started.

--
Wayne
http://www.scantips.com "A few scanning tips"
Anonymous
April 15, 2004 12:24:19 AM

Archived from groups: alt.comp.periphs.scanner (More info?)

Once again, thanks for the info. My scanner is Epson perfection 3170

http://www.epson.com/cgi-bin/Store/consumer/consDetail....






"Wayne Fulton" <nospam@invalid.com> wrote in message
news:D uudnaF4FsW2_eDdRVn-uw@august.net...
> In article <107pg7b55iqrm7c@corp.supernews.com>, dgvxfcsrt@okghbvg.org
> says...
> >
> >
> >
> >
> >Thanks for the info. For your info I have a HP Photosmart printer, it
takes
> >2 colour cartridges, one is the typical tri-color the other is 3 "pastel"
> >colors. When I open up print dialogue it gives me the option of printing
in
> >4800 dpi "optimized" I'm guessing that means the software will "pixelize"
> >the file to create a better photo. On another note, if my printer does
take
> >2 cartridges with more than 3 colors does that affect the 24 bit limit
you
> >mentioned?
>
>
> There is a huge conceptual difference between the printers ink dot ratings
> (like 4800 dpi), and the image's pixel resolution (like 300 dpi, but this
dpi
> term has a very different meaning).
>
> The printers rating is about motor steps to position ink drop dots of 3 or
6
> colors (about ink drops of 3 or 6 colors, not about pixels). This is a
> Quality setting, not really a resolution setting. This number is NOT
about
> image pixels. The 6 colors vs 3 colors does not affect resolution, but 6
can
> help to print photo quality better, so that the lighter ink dots are less
> visible in the lighter colored areas.
>
> The image resolution (like 300 dpi) is about pixels per inch (dpi or ppi
are
> interchangable in this use), where each pixel might be one of 16 million
> colors. This is NOT at all the same thing as ink drop dots.
>
> You want to select one of printers higher quality ratings to print photo
> quality (as opposed to a low quality but fast draft mode setting), but you
> scale images in the ball park of about 300 dpi (pixels per inch) for photo
> quality. Maybe print 300 dpi images at 4800 dpi printer setting.
>
> See http://www.scantips.com/basics3b.html for more about this difference.
>
>
> >I made a mistake in my earlier posting, my scanner offers 48 bit and 24
bit
> >(not 32)
> >
> >I'm continuing to experiment, it seems that for scanning my 35mm slides
I'm
> >tending to settle with 24 bit color @6400 resolution. Keeping in mind
that
> >I'm creating a master digital archive for long term storage, and from
that
> >master file I will create scaled down images for CD/DVD viewing on a
screen
> >such as TV or monitor, However I want to have that digital archive
available
> >to be able to create the most optimum prints for various selected images
> >that family members may request.
> >
> >Am I on the right track here?
>
> I seriously doubt you have a 6400 dpi scanner? But if somehow you do,
then
> there is a special time and place you might consider using it. The concept
is
> that the ratio of (scanning resolution / printing resolution) is the
> enlargement factor. For example, scaling to (6400 dpi scan / 300 dpi
print)
> would give 6400/300 = 21.3X size enlargement, printing about 30x20 inches
> from 35 mm film size. If that is the goal, and if you have a 6400 dpi
> scanner, then that is the right plan (except that such large prints are
not
> normally printed at 300 dpi, because the requirements are so great, and
> printers that size often cannot physically do 300 dpi).
>
> More normally, we might scan 35 mm film at say 2700 dpi and print at 300
dpi,
> for 2700/300 = 9x enlargment. 35 mm film is about 0.9x1.4 inches, so this
9x
> is about 8x12 inches (about A4 size) from 35 mm film. This image size
would
> be about (8 inches x 300 dpi) x (12 inches x 300 dpi) = 2400x3600 pixels,
> about 25 MB.
>
> Again, the purpose dictates this. If you wish to print 8x12 inches, then
this
> is appropriate. If you won't print it 8x12 inches, then it is probably
still
> excessive for the purpose. When scanning prints, enlargement is less
often
> an issue, so we might scan at 300 dpi, print at 300 dpi, for 100% size (no
> enlargement).
>
> Some scanners can output 48 bits, but only a few photo editor programs can
> accept 48 bits, and our printers and video want 24 bits too. I think you
> probably want 24 bits. If you have a 16 bit program (like full Photoshop),
> then some people do like to output 48 bits, correct the tone adjustments,
and
> then convert to 24 bits for printing or archiving.
>
> The site below should be a big help to you getting started.
>
> --
> Wayne
> http://www.scantips.com "A few scanning tips"
>
Anonymous
April 15, 2004 3:12:44 AM

Archived from groups: alt.comp.periphs.scanner (More info?)

In article <107rshjo09noa2@corp.supernews.com>, dgvxfcsrt@okghbvg.org says...
>
>
>Once again, thanks for the info. My scanner is Epson perfection 3170


It has a rating stated as 3200x6400 dpi, which is how it is said for flatbed
scanners to mean that it is a 3200 dpi scanner (3200 dpi is called Optical
Resolution on the Spec page).
The 3200 dpi is the CCD sensor that samples the photo horizontally.
The 6400 dpi is the motor stepping that moves the CCD carriage vertically.


--
Wayne
http://www.scantips.com "A few scanning tips"
Anonymous
April 17, 2004 12:46:40 AM

Archived from groups: alt.comp.periphs.scanner (More info?)

That is the best explanation of the limited value of scanning at higher bit
rates that I have seen. I have been experimenting with this using the 42 bit
setting on my Canoscan4000/Photoshop 7. At the 4000dpi setting this
generates files of over 100mbs in size which, as you point out, have to be
downsampled in Photoshop once adjustments have been made. 42 bit scanning
can be useful for images with a very wide tonal range but for most images
does not yield a significantly better image in terms of the final print.
!