2.2 Digitizing
Another important task of digital photogrammetry is to pro-
duce digital images. There are several ways to do this. There-
fore the authors examine two different kinds of digitizing.
The first one is divided into two steps: (a) to develop the im-
ages and (b) to digitize the resulting slides with slide scanner
MicroTek ScanMaker 45t.
The second one is to use Kodak's Pro Photo CD service.
Digitizing with MicroTek ScanMaker 45t The ScanMaker
45t is a scanner for positive and negative slides up to a size
of 121x121mm?. The company MicroTek specifies for the
ScanMaker 45t an optical resolution of 1000x 2000dpi and a
maximum resolution of 2000x2000dpi because of interpola-
tion. The colour-depth for one pixel and channel is 12bit and
is converted to 24bit per pixel for all three channels R,G and
B. The scanner is equipped with a SCSI-interface and can be
driven with a PC or APPLE Macintosh.
Digitizing with Kodak's Pro Photo CD Eastman Kodak
Company offers different kinds of their Photo CD (Gonsey,
1995). One is the so called "KODAK DIGITAL SCIENCE
Photo CD Master Disc”, which is used for images from 35mm
film only. The possible resolutions are from Base/16 to 16
Base (Table 1).
The other Photo CD is the “KODAK DIGITAL SCIENCE
Pro Photo CD Master Disc". This Pro Photo CD is used
to store images from 35mm, 120, and 4x5 film, which may
be digitized by a KODAK Professional PCD Film Scanner
4045. A Pro Photo CD Master Disc may hold as few as
25 pictures because each picture can optionally contain six
resolutions: Base/16 to 64 Base (Table 1). Therefore films
can be scanned at 6144x4096pixel resolution, depending on
the image format.
Name Resolution File Size | Purpose
(pixels) (MB)
Base/16 128x192 0.07 Index print of
image
Base/4 256x384 0.28 rotated image on
television
Base 512x768 1.13 TV or computer
monitor display
High-definition
television display
(HDTV)
highest resolution
on a Photo CD
Master Disc
only on a Pro
Photo CD Master
Disc
4 Base 1024 x1536 4.50
16 Base 2048 x 3072 18.00
64 Base 4096 x6144 72.00
Table 1: Resolutions of Kodak's Photo CDs
In the authors' project the Pro Photo CD has to be used
because of the special image format of the Pentax camera
(Section 2.1). This format can't be handled with the Photo
CD.
Comparison To estimate the two different kinds of digi-
tizing, the geometrical quality was examined (Heinz, 1996).
Therefore the coordinates of control-points on the film were
measured. This was done with the Zeiss PSK 2 compara-
tor. And also the picture-coordinates in the corresponding
digitized images were measured. To describe the distor-
tions, mathematical functions were used, to do a transfor-
mation from the picture coordinate-system in the slide to the
coordinate-system in the digitized image. The figures 2 and
3 show the resulting residuals — using a plane similarity trans-
formation by overdetermination (Helmert transformation) -
with:
x' = ao + 011 — A2Y
1
y' = bo + b1x + bay (1)
were (z', y') are the coordinates in the digitized image.
cree essei ess
215
10 Pixel /
Figure 2: Residuals of Helmert transformation from slide-
coordinates to the digitized image-coordinates on Pro Photo
CD.
P.
ert 5.0 Pixel
Figure 3: Residuals of Helmert transformation from
slide-coordinates to the ScanMaker 45t digitized image-
coordinates.
In Figure 3 the systematics and the size of the residuals in-
dicate that the slide scanner produces results, which are not
as good as in Pro Photo CD image. But other comparisons
— done with plane affine transformation or 2nd order poly-
nomal — show that the differences are not as much signif-
icant as with the Helmert-transformation. This is because
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B5. Vienna 1996
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