Hi Roy,
> > When you set the setpoints, these 2000 values are then mapped
> out to occupy
> > the entire range. You then apply your tonal curves to the high bit,
> > setpointed data.
>
> Ok, Austin, let's go with your numbers.
> Is the number 2000 now a measure, indication or whatever
> of the dynamic range of the image at this stage?
The number 2000 is the dynamic range of the captured image by the scanner,
yes.
> Read it into PS. Convert 16-bit to 8-bit -- now 256 levels.
That would be a mistake, and severely degrade the image. You would first
apply your setpoints and then your tonal curves. The convert to 8 bits. If
you simply do as you suggest, then you would be causing adjacent image data
values to be wiped out, combined, so you would be decreasing the dynamic
range of the image by doing so, and could get posterization in your output
image.
> Is the number 256 now a measure, indication or whatever
> of the dynamic range of the image at this stage?
Yes, the dynamic range of the resultant image is now 256, but the density
range is the same as the density range of the original image.
> If you answered "yes" to both Dyr questions, does the 8-bit image
> have 1/8 the dynamic range of the 2000 level image?
The scanned image data file had a dynamic range of 33dB, and the processed
file is now 24dB. The processed image file has less dynamic range, of
course.
This is all irrelevant, as we are simply talking about scanning the image,
and the importance of dynamic range when scanning and manipulating the
image. It's well known that we obviously scan at a far greater dynamic
range (for B&W that is) than the human eye can see (but not greater than the
density range), but the reason for that I've explained many times, and is
well accepted as being the right way to do things for B&W. For color,
scanning at 8 bits is probably fine, as I've explained in another post, and
as Dan Margulis argues.
> Austin, we all know how scanners and printers work,
>From your posts, I don't get the impression you do understand.
> Yes, I know how printers work and all that. Simple question:
> If I've got a densitometer that measures an area exactly the same size
> as one dot on the paper, how many possible levels do you expect it to
> be able to report?
That's not relevant, since your eye can not see one dot.
> > Possibly to someone who doesn't understand this, because your
> "answer" is
> > simply a wrong answer. Dynamic range IS unquestionably the number of
>
> Actually, you've had many, many people question the claim,
No, that is revisionist history. Only you and Julian. I have had many many
people agree on list, and everyone that I've discussed this with off list,
who are mostly professional imaging engineers, have the exact same
understanding I do.
> otherwise there
> wouldn't be so many posts about it.
The majority of the dissenting posts only come from you and Julian. The
other posts are typically from people who simply are asking about the issue,
because they have questions based on misinformation they have read, or
simply their own curiosity.
> To date, you're the sole person that
> I know of to actually argue your side of the debate.
Then you are only reading what you want to read.
> >
> >
> > It CLEARLY states that the number of digitization levels is the same as
> > dynamic range, providing you want to digitize down to noise.
> >
> > "The dynamic range is often represented as a log ratio..."
> > "This ratio also gives an indication of the number of
> digitization levels
> > that might be appropriate for a given sensor...Unless there is
> a desire to
> > resolve ... noise".
>
> I see the words "...indication...that might be appropriate..."
> and you translate that to "...is the same as...". Hmmm.
Yes, that's because I understand what is written there, having been working
with CCDs and digital imaging system design for over 20 years. Read it
carefully. That is there simply because you CAN resolve to less than noise,
of course, but if you are resolving TO noise, the dynamic range IS the same
as resolution. If you resolve to more than noise, that does not increase
the dynamic range of the detected signal.
Austin
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