Digital BW, The Print

Comments interspersed below.

----- Original Message ----- 
From: "tzinzunzan2000" <ldmr@...>
To: <DigitalBlackandWhiteThePrint@yahoogroups.com>
Sent: Wednesday, December 05, 2001 11:06 AM
Subject: Re: [Digital BW] 16-bit Scanning: Why?


| First, some questions. By 'combed' histogram do you mean only a 
| histogram that contains gaps all the way from bottom to top or do you 
| include those those histograms which are slightly 'combed', meaning 
| those that have a base throughout most of the histogram but have very 
| narrow (comblike) peaks and valleys?

I mean gaps all or part of the way but not just peaks and valleys.  You will always have peaks and valleys.

 Also, very roughly speaking, how 
| bad does this combing effect have to be before it manifests itself in 
| output?

I know of no predictable formula - very roughly speaking, a gap of 1/4 of the length of the histogram would result in output problems but less than that it depends on the image.  As Dan Margulis suggests, look at the image and not the histogram.

 Second, an observation. I took a greyscale tiff file scanned 
| from my SS4000, opened the file as 16 bit in PS, duplicated the image 
| and then loaded the same two curves into each image. I got the same 
| histogram changes for both images. Won't hazard to guess the 
| significance of this. 

I would guess it was a fairly detailed image without broad expanses of identical tonality.

Also, I've noticed that sometimes if hit the 
| Auto Levels button I get regularly spaced bottom-to-top gaps in the 
| histogram. 

It indicates that Auto Levels has changed the white and black points, but not the middle gray point, so the new spacing between white and black points would be expected to be evenly distributed.

Again, don't place too much reliance on the histogram - rely on the image.

Maris


| 
| --- In DigitalBlackandWhiteThePrint@y..., "Maris V. Lidaka, Sr." 
| <mlidaka@a...> wrote:
| > Yes - that is precisely the cause of the 'combed' histogram.
| > 
| > Maris
| > 
| > ----- Original Message ----- 
| > From: "mtucker508" <mark@m...>
| > To: <DigitalBlackandWhiteThePrint@y...>
| > Sent: Wednesday, December 05, 2001 9:25 AM
| > Subject: Re: [Digital BW] 16-bit Scanning: Why?
| > 
| > 
| > | --- In DigitalBlackandWhiteThePrint@y..., "Austin Franklin" 
| > | <darkroom@i...> wrote:
| > | > What happens when you make tonal adjustments with 8 bits is 
| > | you loose tonal
| > | > values. 
| > | 
| > | 
| > | Would these tones "moving around" and getting shifted be 
| > | responsible for a histogram that had holes in it? (Not that I've 
| > | ever had one, but a friend of a friend told me that *they* had 
| > | some missing areas in *their* histograms...
| > | 
| > | If this is the case, then you certainly have my full-on attention.
| > | 
| > | Mark