R
Roger N. Clark (change username to rnclark)
I thought I would pass on my experience so far scanning large format
images with my new Epson 4870 scanner. Later, I'll post some comparison
images so you can see how good this scanner is. So far my experience
is that it is close enough to drum scans I've had done that I will
use it for almost all my work. It is not quite as sharp on Fujichrome
Velvia as the drum scans I've done, but careful sharpening overcomes
the limit for the most part. However, because it can do 16-bit
compared to the drum scans, I believe it is better because I can
recover more shadow and highlight details.
The problem is that at 16 bits/channel, no scanner software I've used
can scan the full width of a 4x5 transparency at anywhere near the rated ppi
of the scanner. My requirements are 3200 ppi minimum (the scanner does
4800 ppi). In my testing, 3200 ppi gets information important to my
images that 2400 ppi loses. I've tested Epson scan, Silverfast, and
Vuescan, all the latest versions. The limit, as discussed in a recent
rec.photo.large-format and comp.sys.scanners thread, is due to
a firmware limitation in the scanner limiting total bytes per line, and
that limit does not allow the full width of 4x5 to be scanned at 16 bit
except at 2400 ppi. Vuescan, for example, reads 4800 ppi
if you request 3200 then downsamples. Epson scan was the one I used.
I can do 3200 ppi, 16-bits/channel and a 3.4-inch line width.
With ICE turned on, such a scan takes about 1 hour. Then I move the
box over the the other half of the image, with lots of overlap, and
scan a second time, another hour. I make sure the settings are exactly
the same for the two scans. The resulting images are
about 14,820 x 11,740 pixels and 1 GByte. This joining procedure
went well in photoshop CS on a 1.8 GHz win XP box with 2 GB ram
and 600 GB disk.
I combine the two halves in photoshop. The intensity levels match
essentially perfectly: you can't see the join line at all. I have
found that some, but not all scans mis-register by about a half pixel
in blocks of a few hundred scan lines, meaning one block will be dead
on, the next off slightly. I erase the edge of the overlap
image to so it is not straight, add some feathering, and follow
darker portions of the image if possible and the the images go together
without a possibility of finding a join line.
Then, to really push the limits, I mosaiced two such 4x5 images
into a panorama. The result: 23,380 x 11,820 pixels. But here is
where it really became difficult. The combined file size in
photoshop, keeping them as layers was over 2 GBytes and photoshop
would not save the file when I tried. Fortunately it did not
crash either, so I had to feather the join line and merge the
images before the file size dropped below 2 GBytes. I'm using NTFS
(file system) so files can be larger than 2 GB, but photoshop
would do it in standard photoshop format. If someone knows of a way
for photoshop to save such a file (and read it in again later),
please let me know. The final image is 1.62 GBytes.
The problem with mosaicing images is the lens distortions. If someone
knows of software that will do the mosaicing on such large images,
please let me know.
Anyway, Thanks for those in previous threads who helped me work out
the details and limits of the scanner. I will just have to sigh, and
scan in pieces! So here is the final image:
http://www.clarkvision.com/gallerie...orado.fall.c10.01.2003.L4.9536.a+b.c.791.html
If people want more information on the procedure, I'll be happy to
provide it.
Roger Clark
http://www.clarkvision.com
images with my new Epson 4870 scanner. Later, I'll post some comparison
images so you can see how good this scanner is. So far my experience
is that it is close enough to drum scans I've had done that I will
use it for almost all my work. It is not quite as sharp on Fujichrome
Velvia as the drum scans I've done, but careful sharpening overcomes
the limit for the most part. However, because it can do 16-bit
compared to the drum scans, I believe it is better because I can
recover more shadow and highlight details.
The problem is that at 16 bits/channel, no scanner software I've used
can scan the full width of a 4x5 transparency at anywhere near the rated ppi
of the scanner. My requirements are 3200 ppi minimum (the scanner does
4800 ppi). In my testing, 3200 ppi gets information important to my
images that 2400 ppi loses. I've tested Epson scan, Silverfast, and
Vuescan, all the latest versions. The limit, as discussed in a recent
rec.photo.large-format and comp.sys.scanners thread, is due to
a firmware limitation in the scanner limiting total bytes per line, and
that limit does not allow the full width of 4x5 to be scanned at 16 bit
except at 2400 ppi. Vuescan, for example, reads 4800 ppi
if you request 3200 then downsamples. Epson scan was the one I used.
I can do 3200 ppi, 16-bits/channel and a 3.4-inch line width.
With ICE turned on, such a scan takes about 1 hour. Then I move the
box over the the other half of the image, with lots of overlap, and
scan a second time, another hour. I make sure the settings are exactly
the same for the two scans. The resulting images are
about 14,820 x 11,740 pixels and 1 GByte. This joining procedure
went well in photoshop CS on a 1.8 GHz win XP box with 2 GB ram
and 600 GB disk.
I combine the two halves in photoshop. The intensity levels match
essentially perfectly: you can't see the join line at all. I have
found that some, but not all scans mis-register by about a half pixel
in blocks of a few hundred scan lines, meaning one block will be dead
on, the next off slightly. I erase the edge of the overlap
image to so it is not straight, add some feathering, and follow
darker portions of the image if possible and the the images go together
without a possibility of finding a join line.
Then, to really push the limits, I mosaiced two such 4x5 images
into a panorama. The result: 23,380 x 11,820 pixels. But here is
where it really became difficult. The combined file size in
photoshop, keeping them as layers was over 2 GBytes and photoshop
would not save the file when I tried. Fortunately it did not
crash either, so I had to feather the join line and merge the
images before the file size dropped below 2 GBytes. I'm using NTFS
(file system) so files can be larger than 2 GB, but photoshop
would do it in standard photoshop format. If someone knows of a way
for photoshop to save such a file (and read it in again later),
please let me know. The final image is 1.62 GBytes.
The problem with mosaicing images is the lens distortions. If someone
knows of software that will do the mosaicing on such large images,
please let me know.
Anyway, Thanks for those in previous threads who helped me work out
the details and limits of the scanner. I will just have to sigh, and
scan in pieces! So here is the final image:
http://www.clarkvision.com/gallerie...orado.fall.c10.01.2003.L4.9536.a+b.c.791.html
If people want more information on the procedure, I'll be happy to
provide it.
Roger Clark
http://www.clarkvision.com