scanning large format: to the limit (and beyond)

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/galleries...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

In article , "Roger N. Clark (change username
to rnclark)" wrote:

[...] The combined file size in
photoshop, keeping them as layers was over 2 GBytes and photoshop
would not save the file when I tried. [...]

Roger (and others with the same large-file problem), the new Photoshop
(CS) will work with and save images larger than 2gb as an option.

In article , "Roger N. Clark (change username
to rnclark)" wrote:

[...]

Roger - one more thing. Have you considered using the ZoomView feature of
Photoshop (7 and up) to display your web image? That way you can put the
whole image up and we can zoom into segments.

One example: http://arts.winona.edu/i/drake/burwell001.html (probably expired)
And I've one of Brian Caldwell's well known Flat Iron building. (ask for URL)

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

Thanks, looking forward to the examples. The resolution numbers you reported
earlier, seem higher than some of the other users reported. Maybe your
methods of determination are more accurate, and maybe you also got an above
average sample from the inevitable quality spread.

SNIP
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.

That is actually pretty good for a flatbed scanner. The temperature rise
when scanning (causing film expansion), play in the CCD/lens assembly, and
lens distortion, can accumulate to several pixels on other scanners.

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.

In Photoshop it might be done quicker by setting the layer blending mode to
"difference" (meaning equal RGB values are black), but maybe that's what you
already did.

SNIP
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.

Photoshop CS seems to be able to do that with the .psb "Large Document
Format" (up to 300,000 pixels in any dimension, upto 56 channels per file,
all PS features enabled), although the operating system seems to pose a
process limit (not file limit as I presumed earlier) to 2GB, maybe Photoshop
gets around that by dividing between processes.

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.

Haven't tried it on such big files, but I use the combination of Panorama
Tools (http://www.tawbaware.com/maxlyons/pano12ml.htm) and the PTAssembler
GUI frontend (http://www.tawbaware.com/ptasmblr.htm). It also allows the
stitching of plan-parallel offset images and morphing the residual
differences. The author, Max Lyons, did a recompile of Helmut Dersch's
source code to include some additional functionality, so I'd assume he's
capable of addressing particular issues you might run into.

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/galleries...a+b.c.791.html

Lot's of dynamic range! It looks pretty good, thanks for sharing.

Bart

jjs wrote:
In article , "Roger N. Clark (change username
to rnclark)" wrote:


[...] The combined file size in
photoshop, keeping them as layers was over 2 GBytes and photoshop
would not save the file when I tried. [...]


Roger (and others with the same large-file problem), the new Photoshop
(CS) will work with and save images larger than 2gb as an option.

Yes, I did use CS. Thanks to you and Bart, I looked inder
preference, file handling, and found the large format
check box. I wish I knew about that earlier!

Roger

Bart van der Wolf wrote:

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

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.

In Photoshop it might be done quicker by setting the layer blending mode to
"difference" (meaning equal RGB values are black), but maybe that's what you
already did.

Yes. That is the most accurate way in my opinion. It works
very well.

Photoshop CS seems to be able to do that with the .psb "Large Document
Format" (up to 300,000 pixels in any dimension, upto 56 channels per file,
all PS features enabled), although the operating system seems to pose a
process limit (not file limit as I presumed earlier) to 2GB, maybe Photoshop
gets around that by dividing between processes.

Thanks, I now have it enabled. I had assumed the existing psd
format had been extended, bbut it is a whole new format.


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.

Haven't tried it on such big files, but I use the combination of Panorama
Tools (http://www.tawbaware.com/maxlyons/pano12ml.htm) and the PTAssembler
GUI frontend (http://www.tawbaware.com/ptasmblr.htm). It also allows the
stitching of plan-parallel offset images and morphing the residual
differences. The author, Max Lyons, did a recompile of Helmut Dersch's
source code to include some additional functionality, so I'd assume he's
capable of addressing particular issues you might run into.

Thanks, I'll check them out.

Roger

jjs wrote:

In article , "Roger N. Clark (change username
to rnclark)" wrote:

[...]

Roger - one more thing. Have you considered using the ZoomView feature of
Photoshop (7 and up) to display your web image? That way you can put the
whole image up and we can zoom into segments.

One example: http://arts.winona.edu/i/drake/burwell001.html (probably expired)
And I've one of Brian Caldwell's well known Flat Iron building. (ask for URL)

OK, I checked this out. Pretty cool program.
The question I have about this, is how secure is it? It seems
that if you know the structure of the program files, which is easily
done with one test, then one can go to the image directory and
simply download all the tiles and reassemble the complete
image! It tried it and was able to access all of them
easily.

Roger

In article , "Roger N. Clark (change username
to rnclark)" wrote:

jjs wrote:

One example: http://arts.winona.edu/i/drake/burwell001.html (probably
expired)
And I've one of Brian Caldwell's well known Flat Iron building. (ask
for URL)

OK, I checked this out. Pretty cool program.

It's built into Photoshop. The tiles are, as you probably found, JPEG
images with a different file extension.

The question I have about this, is how secure is it? It seems
that if you know the structure of the program files, which is easily
done with one test, then one can go to the image directory and
simply download all the tiles and reassemble the complete
image! It tried it and was able to access all of them
easily.

It isn't secure, of course. In fact, I can think of no way to assure
security of http served images. If one can see an image, he can copy it.

I missed the beginning of this thread (I see it's heavily cross posted). Just wanted to add
something about large images: a while ago I developped an app that displays/manipulates large
image files quickly. It's probably not what you are looking for but might give you an idea. I did
it mainly to access scientific bitmaps.
The freeware is online at http://www.gdargaud.net/Hack/LargeImage.html
For instance I used it to create the images on http://www.gdargaud.net/Antarctica/RadarSat.html
from a 2Gb image file.
and there's even a cgi demo at http://gdargaud.dnsalias.com/RadarSat/LargeImageCgi.exe but it's an
excrutiatingly slow ADSL line.
--
Guillaume Dargaud
http://www.gdargaud.net/
"Eat one live toad the first thing in the morning and nothing worse will happen to you the rest
of the day."

"Roger N. Clark (change username to rnclark)" wrote in
message ...
Bart van der Wolf wrote:

Photoshop CS seems to be able to do that with the .psb "Large Document
Format" (up to 300,000 pixels in any dimension, upto 56 channels per
file,
all PS features enabled), although the operating system seems to pose a
process limit (not file limit as I presumed earlier) to 2GB, maybe
Photoshop
gets around that by dividing between processes.

Thanks, I now have it enabled. I had assumed the existing psd
format had been extended, bbut it is a whole new format.


Is it possible in PS-CS to print files as large as the 300,000 pixel limit?

I mean that if I have a file that is 12,000 x 72,000 pixels can I print that
on my Epson 9600 as a 20 foot panoramic?