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I have a Canon Digital Rebel and I normally capture my images as RAW. At
the moment, I have to convert them to TIFF to edit them in Photoshop. I
have the option of converting to 16 or 8 bit/channel TIFF. Is there any
benefit to using 16 bits/channel? I've always thought that digital cameras
only capture 24-bit color (8 bits/channel). If it would make a difference
with the print quality when printed to a digital printer at Wolf Camera or
similar?

Neal

On Wed, 28 Jan 2004 21:52:41 -0500, "Neal Matthis"
<> wrote:

>I have a Canon Digital Rebel and I normally capture my images as RAW. At
>the moment, I have to convert them to TIFF to edit them in Photoshop. I
>have the option of converting to 16 or 8 bit/channel TIFF. Is there any
>benefit to using 16 bits/channel? I've always thought that digital cameras
>only capture 24-bit color (8 bits/channel). If it would make a difference
>with the print quality when printed to a digital printer at Wolf Camera or
>similar?


It's a matter of where and when you choose to do your
most aggressive tonal corrections. To wit: if you do them
in your RAW conversion program, then save to 8 bits per
color, that works fine. But if you choose to defer those
corrections until later in the game, then have your RAW
converter output 16 bits per channel.

There's no printer in existence that can print using
16 bits per channel, so sooner or later you have to
convert the image down to 8 bits per channel.


rafe b.
http://www.terrapinphoto.com

"Raphael Bustin" <> wrote in message
news:...
> It's a matter of where and when you choose to do your
> most aggressive tonal corrections. To wit: if you do them
> in your RAW conversion program, then save to 8 bits per
> color, that works fine. But if you choose to defer those
> corrections until later in the game, then have your RAW
> converter output 16 bits per channel.
>
> There's no printer in existence that can print using
> 16 bits per channel, so sooner or later you have to
> convert the image down to 8 bits per channel.
>

What then might be the purpose of having a scanner that does 16 bit per
channel scans? If your photo editing requires you convert down to 8 bits,
discarding effectively 8 bits of something, before printing, why not save
time and file space and just scan/save/print everything at 8 bits?

Jim

Canon RAW is 12 bits. You will retain all 12 bits if you import into PS at 16
bits. That will means less loss of quality if you manipulate colour, contrast
etc in PS.


On Wed, 28 Jan 2004 21:52:41 -0500, "Neal Matthis" <> wrote:

>I have a Canon Digital Rebel and I normally capture my images as RAW. At
>the moment, I have to convert them to TIFF to edit them in Photoshop. I
>have the option of converting to 16 or 8 bit/channel TIFF. Is there any
>benefit to using 16 bits/channel? I've always thought that digital cameras
>only capture 24-bit color (8 bits/channel). If it would make a difference
>with the print quality when printed to a digital printer at Wolf Camera or
>similar?
>
>Neal
>

On Thu, 29 Jan 2004 06:31:44 GMT, "JIM" <>
wrote:

>"Raphael Bustin" <> wrote in message
>news:.. .
>> It's a matter of where and when you choose to do your
>> most aggressive tonal corrections. To wit: if you do them
>> in your RAW conversion program, then save to 8 bits per
>> color, that works fine. But if you choose to defer those
>> corrections until later in the game, then have your RAW
>> converter output 16 bits per channel.
>>
>> There's no printer in existence that can print using
>> 16 bits per channel, so sooner or later you have to
>> convert the image down to 8 bits per channel.
>>
>
>What then might be the purpose of having a scanner that does 16 bit per
>channel scans? If your photo editing requires you convert down to 8 bits,
>discarding effectively 8 bits of something, before printing, why not save
>time and file space and just scan/save/print everything at 8 bits?


16 bits per channels is mostly useful if you plan to do
or need to do some really drastic tonal corrections,
or several such corrections in series.

Most scanner drivers and firmware operate with 16 bit
(or greater) math -- so it makes some sense to do the
most drastic tonal moves there, in the driver.

I've never been one to claim great advantages for
16 bit image manipulation. I do my main corrections
in the scanner driver (or RAW image converter) and
work in 8 bits in Photoshop.

There are of course lots of purists who prefer to work
with 16 bit images for as long as possible.


rafe b.
http://www.terrapinphoto.com

>From: "JIM"

>What then might be the purpose of having a scanner that does 16 bit per
>channel scans? If your photo editing requires you convert down to 8 bits,
>discarding effectively 8 bits of something, before printing, why not save
>time and file space and just scan/save/print everything at 8 bits?

'Cause printing is the last step ... you can much of your work in 16 bit mode
(pretty much ALL of it with Photoshop CS) and then drop down to 8 to print.
Good explanation here ...

http://www.creativepro.com/story/feature/7627.html

"Bill Hilton" <> wrote in message
news:...
> 'Cause printing is the last step ... you can much of your work in 16 bit
mode
> (pretty much ALL of it with Photoshop CS) and then drop down to 8 to
print.
> Good explanation here ...
>
> http://www.creativepro.com/story/feature/7627.html

'Preciate that link Bill. Did not like what I read, however. Appears I
haven't done enough homework concerning digital image manipulation. Bruce
wrote his article in Aug 2000, so am not sure how much of it still applies.
Also, do not know if the Epson 2200 can print 16 bit tiff files.........mine
prints something(?); but it could be that photoshop 6 just downsamples
automatically to 8 bits before sending the info to the printer? Also, don't
like not knowing what is being thrown away with those deleted 8 bits.

I am concerned now that I may have 'degraded' some of my images through
various manipulations in photoshop. Was not aware that I was creating
"holes" in my histograms with each change.

Another problem I did experience with one photo: printed out about 10 copies
of a photo on 13" x 19" paper. Printed each individually; i.e., could not
load all 10 at once. Now am wondering if the difference I saw in some of the
prints was not due to photoshop downsampling to 8 bits each time and
discarding different sets of bits for each print? Had bluer water in a
couple prints compared to the greener water of the majority. Also, the bluer
prints had a sharper appearance of the main subject (color more saturated).
Posterization or grain effect, as reported by Bruce, was more noticeable in
parts of the photo also.

An Epson tech rep, BTW, says they have no problems printing '24' bit files
with the 2200, never mind 16??

Did someone mention 'plug and play' printing ease?

Jim

In message <>,
DJ <> wrote:

>Canon RAW is 12 bits. You will retain all 12 bits if you import into PS at 16
>bits.

Not exactly; you lose precision on those 12 bits when you move from a
linear space to a gamma-adjusted one. There are more values possible in
16-bit gamma-adjusted than 12-bit linear, but they are not the correct
precise values necessary, so they are rounded off.
--

<>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
John P Sheehy <>
><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><

writes:

>>Canon RAW is 12 bits. You will retain all 12 bits if you import into PS at 16
>>bits.

>Not exactly; you lose precision on those 12 bits when you move from a
>linear space to a gamma-adjusted one. There are more values possible in
>16-bit gamma-adjusted than 12-bit linear, but they are not the correct
>precise values necessary, so they are rounded off.

There's no practical loss. If you were to convert from 12-bit linear to
16-bit linear, a change of 1 in pixel value in the 12-bit data would
become a change of 16 in the 16-bit data. A 16-bit gamma-corrected code
distributes its available codes differently, but the worst case (least
resolution) happens in the highlights. The one-step difference between
4094 and 4095 in the 12-bit code becomes a difference of 7 in 16-bit
gamma coding (65528 to 65535).

The largest possible rounding error that can be introduced by the
process is one-half code step in 16-bit gamma, which is only 0.07 step
in the 12-bit code. That's completely insignificant compared to the 0.5
step quantization error inherent in the 12-bit code, even with
noise-free computer-generated images. In photographs or scanned film,
the image noise will dwarf both of these errors.

So, for all practical purposes, there is no loss of information, and no
rise in noise level, introduced by converting from 12-bit linear data to
either 16-bit linear or 16-bit gamma encoded data.

Dave

"JIM" <> wrote in message
news:tTdSb.13555$ om...
[snip]
> An Epson tech rep, BTW, says they have no problems printing '24' bit files
> with the 2200, never mind 16??

What he means is 24 *total* bit files, at 8 bits per RGB channel. No
printer that I'm aware of can print high bit (>8 bit/channel) info, because
no OS can send it more than that. PS just dithers to 8 bit if you
accidentally try to output a high bit file.

But, hey, I've got a burning question for you if you actually know an Epson
rep that knows his stuff: ask him/her what the optimum resolution is for
printing: iow, what dpi does the driver send to the printer.

IF he'she knows, and IF he/she'll tell you, you can help solve one of the
world's greatest mysteries!




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