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Re: Apple II Magazines
Alex Lee wrote:
This is a major point raised by Michael - having a black sheet behind
the page you're scanning will greatly reduce the other side of the
page's contents coming through when scanning the page you want. This
will, of course, mean the scan will come out a little darker, but
with some Photoshop restoration, you can make what should be white,
white again, along with black and the complete range of tone between
white and black.
As for using a camera to scan...I've never tried it myself, but
somehow I think you're always going to get better scans with a
flatbed or sheet fed scanner.
"Better" may be true, but "good enough" is the point, and a 10Mpixel
camera will capture enough information that a Photoshop script can
compress the blacks and whites, dropping out the paper texture, and
sharpen it so that it can be saved as, say, an 8-level grayscale
.GIF that has plenty of "ink" info and none of the "paper" info,
ready for a PDF with OCR for searchability.
Some prefer a 1-bit BW representation, but that often requires
resampling to 300 or more dpi just to get clean edges on the fonts,
while 8-level .gifs look fine at 150 dpi.
The speed penalty of a flatbed is a serious problem unless you are
willing to shear the spine and use an ADF overnight.
-michael
Certainly the camera is quicker, if it can capture images completely
flat so that no text is distorted, especially around the spine, which is
likely unless it's held as flat as possible. As has already been
anticipated, that's going to be an issue if you want to keep the
magazine intact and not pull it apart. But you can hold it down flat
enough that in most cases, it shouldn't be too big an issue for a
flatbed scanner - no text should ever go so far into the spine (if it
does, it's probably a poorly designed advert). Ensuring a flat image
will of course help more accurate optical character recognition (OCR).
Photoshop is certainly capable of removing any distortion due to
curvature of the page. Depth of focus is important, so bright lighting
and a small aperture are important.
The professional book scanners that use photography often open the book
just 90 degrees, then use two cameras, each perpendicular to one of the
two "open" pages, to minimize distortion and required depth of field.
For black and white scans, I prefer 1-bit black and white images at at
least 600dpi. You should find that you're still getting very good
compression (if saving as an LZW compressed TIF, or as a PDF) and when
viewing the black and white at that resolution in Acrobat or Mac OS X's
Preview, both programs will create anti-aliasing on the fly and display
a very nice clean image. Additionally, if you were to print such a scan,
you'd also find the print would appear very nearly as good as the
original image, because no permanent unecessary anti-aliasing has been
added to image.
Good point, but at 30 megapixels for an 8.5"x11" page, that certainly
goes beyond affordable cameras. And the only thing you are capturing
at that higher resolution is, in fact, the information that will be
needed to anti-alias into smooth edges.
Might as well capture photographically, with intrinsic anti-aliasing,
and compress with 8-level grayscale. GIF encoding will result in
comparable file sizes and the readability will be excellent.
Or, if you still prefer B&W, scale the photographic page image to
600dpi and threshold it to B&W. You can later convert it back to
an 8-level grayscale image at 300dpi with little loss.
But you're right, I wouldn't like to be the one to manually scan every
page. Using a sheetfed scanner will save time too, but then you won't be
able to use a black sheet behind each page to help prevent the other
side coming through.
As Paul suggested, you can replace the white background on the scanner
with a flat black background and all bleed-through will be suppressed.
The big issue for many is the need to destroy the binding to use an
ADF, or the large investment of time to manually (and imperfectly)
position each page for manual scanning. I think that photographic
capture with scripted post-processing is an excellent way to avoid
either destroying the binding or spending hours in mindless toil.
If there's a sheetfed way that minimises the other side of the page's
print coming through, than I think you'd be onto a winner in terms of
speed and quality.
There is--but the binding must be undone...
Actually, careful thresholding during post-processing can remove most
bleedthrough in B&W areas of the page (though anti-aliasing may be
slightly disturbed). Any areas of grayscale will still be affected
by bleedthrough.
-michael
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