LaserSoft Imaging

It occurs to me that my Nikon LS-20, and probably all scanners, only really operate at a few resolution settings. Programs like SilverFast must then be requesting resolutions at or above what the user requested and downsampling it for the user's final output.

This raises two questions:
1. How can I tell what "hardware" resolutions my scanner operates at, so that I can avoid wasting time requesting, e.g., 1001 dpi when the scanner operates at 100, 1000, and 2000 DPI only? (in this case if the above is correct SilverFast would do a 2000 DPI scan and the resample it to 1001 DPI, possibly introducing unwanted artifacts and scanning more slowly than necessary).

2. If SilverFast is resampling as above, is this where the advantage of having SilverFast do my unsharp masking as opposed to PaintShop comes in?

Thanks, any help appreciated.
Carson

I may have found an answer to my question, above. In part of the SANE source code (see http://www.mostang.com/sane) for Nikon scanners is the following definition:

static const SANE_Int resolution_list[] =
{
25,
2700, 1350, 900, 675, 540, 450, 385, 337, 300, 270, 245, 225, 207,
192, 180, 168, 158, 150, 142, 135, 128, 122, 117, 112, 108
};

This is what SANE calls the "preferred resolutions" for this scanner. If anyone knows different or better, please let me know. I can believe 2700, 2350, and 900, but I wonder about the 108, 112, 117 series. Are these all multiples of something? Not that I can see.

I also have no idea why the numbers are in this order.

Any leads appreciated.

Carson,

I'm not sure why you need such information, but you can figure the answer yourself with only very simple maths. Remember theres is no such thing as part of a pixel

Possibilities include:-

2700/2, 2700/3, 2700/4, etc. You'll get sensible numbers down to 2700/6 You can do the maths from there on down.

Ian

<font size=-1>[ This Message was edited by: ilyons on 2001-09-22 00:40 ]</font>

Thanks, Ian, that simplifies things quite a bit. I've since noticed that if I use SilverFast's scan resolution slider, it automatically preselects that "preferred" resolutions of my scanner (2700, 1350, ...).

This makes sense if I've set scaling to 100%, since the slider will then cause my output resolution to match the scanner's. So, for example, using pixel as the measurement unit, if original=450 and scale=100%, with a q-factor of 1 and scan-resolution set to 450 dpi, I'm getting the scanner's direct output of 450 pixels.

If I now set scale to, e.g., 120%, SilverFast's resolution slider still stays at 450 dpi. I suppose the way I'm now getting (in this example) 540 pixels of output is that SilverFast is resampling up to this resolution, since the framed area in my preview screen has not changed.

But (again in this example) probably what I would REALLY want to do would be to change the Scan Resolution to 540, and leave scaling the same. This way I would get 540 dpi of scanner output, instead of 450 dpi of scanner output resampled to 540 dpi with software.

That is, if I understand correctly how SilverFast operates. Does this make sense? Am I correct?

The other question, still unanswered, is: suppose I select an output resolution of 50%, theoretically causing SilverFast to resample the original scan DOWN to 50% resolution. Does using SilverFast's built-in unsharp mask make more sense here than using PaintShop's because the mask will be applied BEFORE the resample? Or, actually, does it make sense even if SilverFast is resampling UP (because it's dealing with the original hardware output rather than a resample as PaintShop would be)?

Thanks in advance,
Carson

On 2001-09-23 19:16, Carson Wilson wrote:


This makes sense if I've set scaling to 100%............... scanner's direct output of 450 pixels.

If I now set scale to, e.g., 120%, SilverFast's resolution slider still stays at 450 dpi. I suppose the way I'm now getting (in this example) 540 pixels of output is that SilverFast is resampling up to this resolution, since the framed area in my preview screen has not changed.

You are allowing SilverFast to resample.

But (again in this example) probably what I would REALLY want to do would be to change the Scan Resolution to 540, and leave scaling the same. This way I would get 540 dpi of scanner output, instead of 450 dpi of scanner output resampled to 540 dpi with software.


That is, if I understand correctly how SilverFast operates. Does this make sense? Am I correct?

Hmm, you went round the world in 80 words and confused the hell out of me, but setting SilverFast for 540ppi at 100% is what you want and 450 ppi at 120% isn't what you want.

The other question, still unanswered, is: suppose I select an output resolution of 50%, theoretically causing SilverFast to resample the original scan DOWN to 50% resolution. Does using SilverFast's built-in unsharp mask make more sense here than using PaintShop's because the mask will be applied BEFORE the resample? Or, actually, does it make sense even if SilverFast is resampling UP (because it's dealing with the original hardware output rather than a resample as PaintShop would be)?

At the risk of causing offence when none is intended - Paintshop Pro's USM is a not on the same planet as the SilverFast USM tool. SilverFast USM uses Lab mode and with careful choice of settings you can get a fair amount of sharpening for little or no artifcats. Unfortunately it takes while to figure what all the settings are doing. However, scanning at such low resolutions is not the ideal route if you intend to use USM at scan stage. I think you would be MUCH better to scan at full resolution, edit your image as required and then create a low resolution duplicate. So far as upsampling is concerned - NOT a wise move, especially if the scanner can give you REAL data up to a resolution well in excess of 540 ppi.



<font size=-1>[ This Message was edited by: ilyons on 2001-09-23 21:13 ]</font>

Nikon Scan Manual for LS2000/LS30 scanners states, on p. 122, that the scanner can scan at any resolution of 2700/N dpi (max rez divided by N), where N is an integer (that is 1, 2, 3, ...). For all other resolutions the Nikon Scan performs interpolation.





<font size=-1>[ This Message was edited by: Tomaz Klinc on 2001-09-23 22:08 ]</font>

Ian and Tomaz - thanks, your info. is great!

Ian, I didn't know SilverFast uses LAB mode sharpening. Does this mean it sharpens only the Lightness channel as you suggest for PhotoShop users? I'll give it another try.

I didn't mean to generate confusion. It had not dawned on me previously that the scanner only works at a few discrete resolutions, and I think this is something SilverFast users should understand. As mentioned above, we might otherwise mistakenly tell SilverFast to upsample a 900 dpi scan to 1340 dpi when 1350 dpi is the more desirable setting.

Another note - if you ignore the scan resolution slider and type a number into SilverFast's scan-resolution input field, you can tell it to scan at any given resolution; what you're really telling SilverFast it seems is to upsample for you.

Anyway, it's really liberating to finally know how this is working!

Carson

Tomaz

here N is an integer (that is 1, 2, 3, ...)

Except integer values that result in 2700/N = a non integer value. Examples include 7, 8, 11, 12, 13, 14, 16... remember we can't half fractional pixels, Hence my comment above. It looks like the Nikon manual has a few mistakes in it as well

Ian

<font size=-1>[ This Message was edited by: ilyons on 2001-09-24 18:21 ]</font>

Ian, I knew the last word would be yours
Of course, it's hard to understand why one would wish to spend a bundle and than scan at 2700/7 dpi.

Of course, it's hard to understand why one would wish to spend a bundle and than scan at 2700/7 dpi.

My sentiments exactly.

Ian (wondering who's been offended, but not getting to worried )

<font size=-1>[ This Message was edited by: ilyons on 2001-09-24 19:15 ]</font>