Digital BW, The Print

Well it's brought out that I was under a false impression about raw data and
histograms, especially in light of the fact there was a justification
option.

I was always of the assumption that the raw data was invariably contiguous,
and therefore, the more it filled a histogram, the more tones you had to
work with. So I assumed that the larger it's span across the histo the
larger it's DR, ergo, the better the scan. Now I learn there is more than
one way to represent the data, and while it may look different it will
function essentially the same. IOW, one is no better than the other from a
quality standpoint, is that right?

If I adjust the setpoints of low bit justified data, to make it's histogram
look like that of the same scan which was high bit justified, would the gaps
appear in the same places as the high bit justified data, would the two
files be the same at that point?

I assume the Leaf is low bit justified, right? Are most?

Martin had sent me two raw files from the same image scanned on two
different scanners. I don't remember if both scanners have the same bit
depth though; lets assume they do. Before manipulations one's histogram
seemed much narrower than the other, so I naturally assumed the scan with
the wider histogram was the preferable scan. However, I casually expanded
each one to look decent, not even trying to make them look exactly alike,
and when I checked their histos after the adjustments I was surprised at how
alike they looked. Should I now assume that one scanner probably just low
bit justified the data, while the other high bit justified it's data?

Was this the conclusion of the discussion you were having with mike
yesterday, where, like you, I thought he was suggesting that scanners do
something of an auto levels on the data, but he was referring to something
else. Was it that he meant he thought most scanners should high bit justify
their data because it makes for a more full looking 8-bit histogram, which
would better impress novices like myself?

Thanks,
Todd



>>>> Another thing I need clarification on is low-bit vs high-bit
>>>> justification.
> 
>> I'm not quite there yet. But this is one of the
>> areas of this conversation I'd really like to understand, at least
>> superficially. Maybe if you speak a little to pros and cons of one over
>> another?
> 
> Hum.  Pro's and con's.  I don't know that there are any, per se, it's just a
> way of storing the values.  Let's see if I can come up with some ;-)
> 
> You can't really make tonal adjustments on the low bit justified
> data...because there are no gaps between the data...what you would do with
> low bit justified data is set the setpoints, and then spread it out evenly
> over the entire 16 bit range.  You could do the same with high bit justified
> data...but with high bit justified data, it's already spread out so before
> doing setpoints, you could do "some" level of tonal moves...not that you'd
> want to without setting the setpoints first.
> 
> Low bit justified data would occupy a VERY small span of an 8 bit
> histogram...where high bit justified data would occupy a region, say it was
> 12 bit data, then when high bit justifying the 12 bit data, the region would
> be 16 times wider (4 bits is 16 times larger)...with 15 gaps in between
> every valid data value.
> 
> Did that help?