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RE: [APML] Wondering about histograms
>I use PolacolorInsight with a Polaroid SS4000. I wonder if acquiring
>Vuescan or some other scanning-control software would give me more
>latitude when it comes to scanning, at least for positives.
Hi Alan
First of all, could you tell us how do you scan your images? 12bits RAW?
If so, and you see this difference between latitudes, I strongly think that this is not a software problem. It doesn't matter how do you manipule the data, what is important is how the CCD sensor sees your film media and traslates that to digital data. So, if your raw scans (true raw scans) have data loss due to lack of dinamical range (latitude), there is no way that any other scanning setting would recover them. As far as I know, every paramether is a post-scanning procedure. The only way that you may recover that data would be to change the scanner's light intensity.
>It seems that whenever I scan a slide (or a slide-mounted negative),
>the histograms tend to be very narrow and steep. When scanning
>negatives the histograms are much wider.
A few film facts: negatives ussually have a much wider dinamical range (latitude). In terms of light intensity, it may be up to 10 times (3-4 steps... please correct me anyone if I am wrong). So, from this point of view, histograms of raw scans may be much wider with negatives than positives.
But, I guess that when you are comparing the histograms, you are not doing that with the boundaries, but with the width of the gaussian like curve of the background. So the question here is how wide is the range of intensities (densities) that the background occupies? It depends on the response of that particular film, the HD curve.
>What I want to know is if that is normal. Whether it is or isn't, is
>there a way to broaden the histogram of positives?
Don't worry too much about that.
If you scanned your image as RAW, and saved it as a 16bits TIFF, you'll see that there is a lot of information in there, even with positives. Just play with the middtones balance and curves to spread the information in a wider range.
BTW, it is a very good idea to do multiple scans of your data, and then average them, or median combine. You'll have to register the images, of course.
Regards,
Carlos Milovic F.
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