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Optimized web images are scanned at the highest possible resolution. However, the advantage of higher resolutions diminishes rapidly after 2-3 multiples.
These images were scanned from a 35-mm slide (a positive transparency). The images presented here were cropped and magnified from the original scan, but were rendered by JPEG compression to yield approximately the same final digital size (13.4 to 13.7 kilobytes).
For example, the second image (1 x scale) was cropped from a 675 pixels-per-inch scan. Because the final rendering on web pages is 72 or 96 pixels-per-inch, the original scanning resolution can accommodate several times magnification with little reduction in quality. The 1350 pixels-per-inch (2 x) scan is noticeably sharper than 675 pixels-per-inch, and the 2700 pixels-per-inch scan is better, but not significantly better, than 1350 pixels-per-inch.
For full-scale rendering (not cropped) of web images, 1012 pixels-per-inch scanning of transparencies is generally sufficient for full-scale rendering of web images. For example, if the full 35-mm width were available, this would result in a web image of 1394 pixels wide x 837 pixels high. Considering that the final rendering of web images should be generally 280-440 pixels wide, this is more than enough to accommodate a 2-3 multiple of the final rendered dimensions. For cropped and magnified images, however, scanning resolutions higher than 1012 pixels-per-inch are necessary.
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Image scanned at 0.5 x scale,
337 pixels-per-inch,
final
rendering 13,639 bytes.
Five mounted police officers
are departing Haulover Beach
but only the closest horse is
clearly distinguishable down
to the hooves.
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Image scanned at 1 x scale,
675 pixels-per-inch, final
rendering 13,512 bytes.
What had been a smear of
vegetation is now a textured
pattern of leaves. Electrical
wires are faintly resolved.
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Image scanned at 2 x scale,
1350 pixels-per-inch,
final
rendering 13,572 bytes.
Notice that the word
"POLICE" is
legible
on
the
back of the closest
officer
and the ponytail on
the
second officer
is resolved
to the point of displaying
her hair tie. At least three
electrical wires are resolved.
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Image scanned at 4 x scale,
2700 pixels-per-inch,
final
rendering 13,487 bytes.
There is little improvement.
The
creases on the shirt
of the man on the left are
more distinctive. Lettering
on the sign is sharper, but
still not readable.
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