Digital BW, The Print

Hi Austin,

On Tuesday, January 7, 2003, at 07:41 PM, Austin Franklin wrote:

> Hi Kevin,
>
>>> That is true of the consumer scanners you and I use.  There are some
>>> scanners, and I've designed one, that have analog gain control 
>>> between
>>> the
>>> CCD and the A/D, and has, basically, hardware setpoints.
>>
>>
>> That would be add a whole new meaning to the auto-exposure function!!
>
> I am surprised none of the current "high end" consumer scanners do 
> it...it
> just isn't that hard, or costly.
>
>>>> Cool, thanks for the primer.  Wouldn't the software use some 
>>>> algorithm
>>>> to interpolate values for the gaps instead of leaving them empty?
>>>
>>> That is a good guess, but no...remember, every pixel has a value
>>> associated
>>> with it.  What are you going to interpolate?  If you did somehow
>>> interpolate, you are giving data that was the same, different values,
>>> or
>>> creating NEW data that didn't exist before...  The gaps really don't
>>> mean
>>> anything, as you are taking the N bit data and converting it to
>>> CONTINUOUS 8
>>> bit data...in other words, when you go to print, you DO have every 
>>> data
>>> value from 0-255 (or most every one).
>
> BTW, did you understand that?  It isn't an easy thing to 
> understand...so if
> you didn't, I can try to give a usable example.

Yes, when I said fill in the gaps I had a image of a histogram with 
nasty gaps that could be interpolated.  But as you say, if you 
interpolated a value to fill a histogram gap, what pixel would you 
assign it to. <sheepish grin>

>
>> Just let me make sure I have understood what you are saying and that 
>> we
>> do in fact agree.  In the same hypothetical the N-1 development
>> (density range of .7), the N development (density range of 1) and the
>> N+1 development( density range of 1.5) all produce virtually the same
>> scan after set points are applied.
>
> Hum.  I don't know what you mean by "same".  The data for the .7 
> density
> range will be "narrower", meaning, say values from 100-240, vs 1, which
> would give you 100-440 vs 1.5, which would give you values from 
> 100-600 (I
> am making up the numbers, they just illustrate that you get more 
> different
> data values, as in a wider range of data values, the more density you 
> are
> scanning.

OK.  We are following the same line of reasoning.  Where that reasoning 
leads you to  depends on the numbers.  Tomorrow I will take a 'normal' 
scene, develop N-1, N and N+1 and see what the numbers look like.  I 
think we need an actual in place of my hypothetical.

>
>> With an extremely shallow exposure/density curve you may have too few
>> discernible points from the scanner to fill the 256 data points
>> (assuming 8bit).
>
> Correct!
>
>> As a principle more data points (ie maximum density
>> range) is better.
>
> Yes.
>
>> Except in situations with an extreme brightness
>> range adding development time to your 'normal' time (or the
>> manufacturers recommended time if you haven't done any testing at all)
>> will increase the density range. And be a good thing.
>
> Yes, but what's the "except" for?  This statement, and the previous 
> one ("As
> a principle...") are the same, are they not?
>
> Regards,
>
> Austin
>
>
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