converting color slides to digital

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Gina
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converting color slides to digital

Postby Gina » Wed May 21, 2003 11:41 am

Hi,

I'm currently trying to convert my color slides from years ago to digital. So far capturing them from a ligthbox with my canon g3 works just fine. I'm quite pleased with the work the camera does but the greater dynamic range of the slides gives me dark images . I capture them like that because otherwise the lighter parts of the slide are "burned" out and the information is lost. Does somebody know the best procedure for converting the image information to get a good result? I played with contrast, saturation, lightness etc but the result is not to my liking.
Thanks up front for any reply's
:)

HaraldHeim
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Postby HaraldHeim » Wed May 21, 2003 5:44 pm

If you need to capture the slides with low exposure settings to avoid overexposed areas, you should at least use the RAW file feature of the G3. That way you get 12 bit instead of the 8 bit per color channel that is used for JPG files.

So even if the upper 4 bit of the 12 bit aren't really used because of the low exposure settings, you still have potential 8 bit of color information. Now what you need to do with the RAW files is to convert them to 16 bit TIFF files and import them into a image application that supports 16 bit per channel. In that image application do a histogram stretch to make the photo bright again.

This method migh produce better results than before, but you will probably still get better results by scanning your slides with a flat-bed scanner or film scanner.

Gina
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digitizing slides

Postby Gina » Mon May 26, 2003 8:21 pm

Hi,

Thanks for the suggestions, Harald, but I don't quite understand what you mean with "stretch". When I see the histogram it allready is stretched all the way. When I stretch it more I'll lose more information, don't I?
I'll try something I read in a Carl Volk article : change to lab mode; copy the lightness channel and change back to rgb. Paste the lightness channel under the original layer and change the blending mode of this original layer to color.
I tried to hire a film scanner but can't find it. I tried scanning the slide with a Agfa Duoscan flatbed scanner but it was not good. Since I stopped using slide film years ago I don't want to buy a film scanner.

Thanks and bye

HaraldHeim
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Postby HaraldHeim » Tue May 27, 2003 8:17 pm

By histogram stretching I mean that to move the triangles below the histogram inwardly. At both ends of the histogram curve there is usually a small line and there is a peak in the middle. Move the triangles until the slope of the curve increases. This removes only a few details in the dark and bright areas if not done too extremely, but generally gives the image a better look.


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