scanning large format: to the limit (and beyond)

Roger N. Clark (change username to rnclark) wrote:
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 is a computer one, file pointers are usually signed long
integers, on a standard 32bit PC that means the pointers can hold a
maximum value of 2,147,483,647 or 2GB-1. Most modern operating systems,
can handle larger files, Linux can be setup to use longer pointers, IIRC
Windows uses a shifting mechanism but, in either case the software needs
to be built to do this. Considering that even medium format digital
cameras are only producing 20MB files at this point, 2GB is a reasonable
software limit. Some of the stitching programs may be able to go
larger, but your dealing with a pretty unweildy image size, none the less.

Paul

"Paul Schmidt" wrote in message
. ..
SNIP
Some of the stitching programs may be able to go
larger, but your dealing with a pretty unweildy image
size, none the less.

Indeed, but the result is rewarding.
This is another way to achieve resolution with a light kit to travel:
http://www.tawbaware.com/maxlyons/gigapixel.htm

Bart

Bart van der Wolf wrote:

"Paul Schmidt" wrote in message
. ..
SNIP

Some of the stitching programs may be able to go
larger, but your dealing with a pretty unweildy image
size, none the less.


Indeed, but the result is rewarding.
This is another way to achieve resolution with a light kit to travel:
http://www.tawbaware.com/maxlyons/gigapixel.htm

Bart

Yes, and though unweildy today, not necessarily tomorrow.
It takes me several hours of work to dodge and burn, contrast stretch,
fix film/dust defects on a large format film scan. I won't go back,
so I'll do the best I can the first time. I've been doing ~3300
ppi drum scans of large format for years, starting on a 100 MHz
Pentium I with 256 megabytes of ram, working with 650 mbyte
files. It's a piece of cake now compared to then! Once 64-bit
systems and software are here these images will be easy.

The 32-bit limit is a real pain. I deal with that at work
most days, and retrofitting software takes a lot of time.
I'm hoping for that 10,000 x 10,000 pixel display on my
wall so I can work on my 25 gigabyte Mars image at one time.
Its now in multiple pieces and I can see only a postage stamp
section of it at one time!

Roger

"Roger N. Clark (change username to rnclark)" wrote in
message ...
SNIP
The 32-bit limit is a real pain. I deal with that at work
most days, and retrofitting software takes a lot of time.
I'm hoping for that 10,000 x 10,000 pixel display on my
wall so I can work on my 25 gigabyte Mars image at one time.
Its now in multiple pieces and I can see only a postage stamp
section of it at one time!

You need a bigger screen ;-)

You probably know this site:
http://pdsmaps.wr.usgs.gov/PDS/publi...l/marslvls.htm

Bart

Bart van der Wolf wrote:

"Roger N. Clark (change username to rnclark)" wrote in
message ...
SNIP

The 32-bit limit is a real pain. I deal with that at work
most days, and retrofitting software takes a lot of time.
I'm hoping for that 10,000 x 10,000 pixel display on my
wall so I can work on my 25 gigabyte Mars image at one time.
Its now in multiple pieces and I can see only a postage stamp
section of it at one time!


You need a bigger screen ;-)

You probably know this site:
http://pdsmaps.wr.usgs.gov/PDS/publi...l/marslvls.htm

Bart


Yes, thanks. But my full resolution maps are not yet published. They
are global mineral maps from Mars Global Surveyor data.
http://speclab.cr.usgs.gov/

Roger

Bart van der Wolf wrote:

"Roger N. Clark (change username to rnclark)" wrote in
message ...
SNIP

The 32-bit limit is a real pain. I deal with that at work
most days, and retrofitting software takes a lot of time.
I'm hoping for that 10,000 x 10,000 pixel display on my
wall so I can work on my 25 gigabyte Mars image at one time.
Its now in multiple pieces and I can see only a postage stamp
section of it at one time!


You need a bigger screen ;-)

You probably know this site:
http://pdsmaps.wr.usgs.gov/PDS/publi...l/marslvls.htm

Bart

Perhaps you should read the article about the guy who shoots with a
special camera he built himself. LARGE format (9" by 18"). Scans are
over a gigabyte. He likes to print large.

In article , Ron Hunter
wrote:

Perhaps you should read the article about the guy who shoots with a
special camera he built himself. LARGE format (9" by 18"). Scans are
over a gigabyte. He likes to print large.

Old hat. He's just another recent press-monger.

In article ,
says...

In article , Ron Hunter
wrote:

Perhaps you should read the article about the guy who shoots with a
special camera he built himself. LARGE format (9" by 18"). Scans are
over a gigabyte. He likes to print large.

Old hat. He's just another recent press-monger.

It is interesting that his 5ftx10ft mural is only 360ppi, hardly heady stuff.
The teacher at New York's New School that uses 2 gig files to print 16x20s is
the one doing new stuff.

Tom

In article ,
(Tom Monego) wrote:

It is interesting that his 5ftx10ft mural is only 360ppi, hardly heady stuff.
The teacher at New York's New School that uses 2 gig files to print 16x20s is
the one doing new stuff.

I don't understand, Tom. What large printer does better than 360ppi?

I don't understand the comment either. I print to approx 50" X 65" with
a ColorSpan 11 head/color (quad K) printer with each head rated at 600 dpi.
The company insists that 300 ppi files are the proper size for this printer,
no matter what the viewing distance. And, actually, the prints are
absolutely gorgeous even on closest inspection.
Www.jvee.com
On 5/27/04 6:23 AM, in article
, "jjs"
wrote:

In article ,
(Tom Monego) wrote:

It is interesting that his 5ftx10ft mural is only 360ppi, hardly heady stuff.
The teacher at New York's New School that uses 2 gig files to print 16x20s is
the one doing new stuff.

I don't understand, Tom. What large printer does better than 360ppi?

--
J Vee