[filmscanners] Re: Dynamic range
on 8/29/02 5:26 AM, David J. Littleboy wrote: but do you realize that the range that Austin is using as his Dmin for the ISO formula is the ENTIRE density range of the scanner? Austin's explained this: in any dynamic range calculation, the maximum signal level can be seen as corresponding to the range of levels handled, assuming the minimum level is defined. The noise (or minimum recognizable signal level) (and the maximum signal level) defines how many meaningful steps the maximum signal level is from the minimum signal level. That's all dynamic range is: the number of meaningful steps from min to max. That's normally expressed as a ratio... Yes, I suppose if one is convinced that DYR is a resolution that is the way they'd have to approach it as such, but David, tell me, have you seen a cited reference that supports that approach? I've wanted to believe Austin is right for a long time, but there is just massive evidence against it. Do you really see the ISO's: (Dmax - Dmin) supporting that, or Analog Devices: (Peak Level) - (Noise Floor) supporting that? Isn't it more obvious to presume that Dmin is a single value, as is Peak Level, and if they WERE a range extra attention would be paid to that issue by the definitions? Would they really leave it vague for most EEs to be mistaken? What Julian said about the term Dynamic Range makes sense: if it's not really a range, wouldn't the definitions go out of their way to have it be known it is a resolution, a resolution which is called a range, and as such all max signal levels need to be understood as being relative to min signal levels before they can be applied in the equation? Shouldn't they hint somehow that while the equation they lay out may look like x/z, or x-z, what it will look like in use will be (x-y)/z or (x-y)-z? In time wouldn't the confusion of students of the subject demand they pay attention to this possible source of massive confusion (and upset ;-)) ??? My point is that a value reported by a scanner corresponds to a range of possible values in the film, and that the size of that range is given by the worse of the noise in the electronics or the bit resolution of the scanner. I think we all share that point. Todd PS, I like the way your mail program quotes me, what do you use? Unsubscribe by mail to [EMAIL PROTECTED], with 'unsubscribe filmscanners' or 'unsubscribe filmscanners_digest' (as appropriate) in the message title or body
[filmscanners] Re: Dynamic range
At 14:53 30/08/02, David wrote: Does that mean you claim that density range and dynamic range are equivalent measurements of the same physical quantity? Well yes and no. Density range is normally a property of a slide or piece of film, or an image on a film. Dynamic range is normally a property of some processing device, like a scanner in this case. If you have a slide that can just be scanned by a scanner without the scanner saturating or getting the black bits lost in the noise, then the slide's density range is the same as the scanner dynamic range, in that case. A scanner doesn't have a density range, but it has a range of densities that it can handle. The maximum range of densities that it can handle in a single pass is its dynamic range. The maximum range of densities that it can handle under any circumstances is it's static range, or max range, sometimes called just Dmax by manufacturers. (Inaccurately, but we think we know what they mean. Dmax is not a range, it is a figure. When they say this, they are by implication assuming an upper limit of 0dB as the other end of the range). So if a slide's density range is greater than the scanner dynamic range then the scanner cannot capture the whole density range of the slide. I am using the terms as they are normally used. Both are measures of range of densities. One is the range of densities actually or potentially on a slide, one is the range of densities that a scanner can handle. You *can* talk about the dynamic range of a particular slide and be kind of correct. Or you could talk about the dynamic range of the medium (that is, the particular film). Dynamic range is, as it always has been, nothing more than the range of largest signal to smallest signal, usually expressed as a ratio. On an actual slide it is easy enough to pick the largest signal (the lightest density) and the smallest signal (the densest area which is just discernable against unexposed film background). For the medium, the relevant figures are the lowest POSSIBLE density, and the highest POSSIBLE density that can still be discerned from background black. If you use the language this way, then the slide's dynamic range is the same thing as its density range. Julian Julian Robinson Canberra, Australia http://members.austarmetro.com.au/~julian/ Unsubscribe by mail to [EMAIL PROTECTED], with 'unsubscribe filmscanners' or 'unsubscribe filmscanners_digest' (as appropriate) in the message title or body
[filmscanners] Re: Dynamic range
Todd Flashner [EMAIL PROTECTED] writes: Yes, I suppose if one is convinced that DYR is a resolution that is the way they'd have to approach it as such, but David, tell me, have you seen a cited reference that supports that approach? http://www.chipcenter.com/dsp/DSP000329F1.html The dynamic range of a digital signal is the ratio of the maximum full-scale signal representation to the smallest signal the DSP or data converter can represent. For an N-bit system, the ratio is theoretically equal to 6.02N. I've wanted to believe Austin is right for a long time, but there is just massive evidence against it. Do you really see the ISO's: (Dmax - Dmin) supporting that, or Analog Devices: (Peak Level) - (Noise Floor) supporting that? You left out the subscripts: (Peak Level)dB - (Noise Floor)dB. As has been said before, those are log values. Subtraction of log values _is_ division. Thus the dynamic range, by those definitions, is exactly the same as it is everywhere else: the ratio of the max signal to the noise. Isn't it more obvious to presume that Dmin is a single value, as is Peak Level, and if they WERE a range extra attention would be paid to that issue by the definitions? Would they really leave it vague for most EEs to be mistaken? It's not vague, it's correct What Julian said about the term Dynamic Range makes sense: if it's not really a range, wouldn't the definitions go out of their way to have it be known it is a resolution, a resolution which is called a range, and as such all max signal levels need to be understood as being relative to min signal levels before they can be applied in the equation? Shouldn't they hint somehow that while the equation they lay out may look like x/z, or x-z, what it will look like in use will be (x-y)/z or (x-y)-z? In time wouldn't the confusion of students of the subject demand they pay attention to this possible source of massive confusion (and upset ;-)) ??? Dynamic range is _equivalent_ to a bit depth because a digital representation at a given bit depth has a quantization error, or quantization noise, of +/- 1/2 lsb. Thus a bit depth involves an implicit noise level of exactly one unit over the range of values it can represent. Thus dynamic range (a logarithm of a ratio) and bit depth (which is the base 2 logarithm of it's largest value) are _equivalent_. PS, I like the way your mail program quotes me, what do you use? I insert the by hand, since depending on the headers, dear old brain dead Outlook Express fails to insert the normal quote marks. G. David J. Littleboy [EMAIL PROTECTED] Tokyo, Japan Unsubscribe by mail to [EMAIL PROTECTED], with 'unsubscribe filmscanners' or 'unsubscribe filmscanners_digest' (as appropriate) in the message title or body
[filmscanners] Re: Dynamic range
Todd Flashner [EMAIL PROTECTED] writes: Yes, I suppose if one is convinced that DYR is a resolution that is the way they'd have to approach it as such, but David, tell me, have you seen a cited reference that supports that approach? David replies: http://www.chipcenter.com/dsp/DSP000329F1.html The dynamic range of a digital signal is the ratio of the maximum full-scale signal representation to the smallest signal the DSP or data converter can represent. For an N-bit system, the ratio is theoretically equal to 6.02N. Julian comments: This quote says nothing about resolution, it is not saying that dynamic range is a resolution, it is saying that the dynamic range is a range between the max and the smallest signal. Nothing new here. I don't know what the 6.02N is about, the ratio is theoretically 2^N (2 to the power N) This ratio calculation will give you the dynamic range AND the resolution in this case. (But don't forget, this does not mean that dynamic range is the same thing as the resolution!!!) Julian Canberra, Australia http://members.austarmetro.com.au/~julian/ Unsubscribe by mail to [EMAIL PROTECTED], with 'unsubscribe filmscanners' or 'unsubscribe filmscanners_digest' (as appropriate) in the message title or body
[filmscanners] Re: Epson 2200 does it exist?
I am pretty sure it exists, I have one sitting in my office! :-) I got lucky and got one out of the some of the first that arrived at BH. They are around... -- Mark Graf Graf Nature Wildlife Photography www.grafphoto.com Unsubscribe by mail to [EMAIL PROTECTED], with 'unsubscribe filmscanners' or 'unsubscribe filmscanners_digest' (as appropriate) in the message title or body
