CALIBRATION OF DIGITAL IMAGES PRODUCED WITH THE USE OF UMAX 1200 SE SCANNER 
Adam Boron 
Dr. Eng., The Department of Photogrammetry and Remote Sensing Informatics 
University of Mining and Metallurgy, Al. Mickiewicza 30, 30-059 Kraköw, Poland 
Commission |, Working Group 5 
KEY WORDS: Scanner, Calibration, Pixel, Pattern, Accuracy, Digital Image 
ABSTRACT 
As a result of the analysis of geometric deformations of digital images acquired using low cost scanner UMAX 1200 
SE, the correction method is proposed which reduces scanning geometric errors from m, = +5 pixels to mp = +0.15 
pixels = +3 um. The correction is executed in two stages. In the first stage are determined l-order corrections d,, dy, 
being steady for each point of the scanner plate and determined during precalibration process. Next are determined d, 
correction of ll-order, being variable for each scanner run, but on certain digital image being constant along the sensor 
line and changeable for different sensor line position. 
1. INTRODUCTION 
Digital photogrammetry deals with processing of photo- 
grammetric photos, as well as semi-metric and non- 
metric images given in a digital form. One of the method 
of gaining the digital images is scanning the original 
photo using different scanner type. Scanner which are 
used to gain the digital image for digital photogrammetry 
purposes should be characterised by the following 
feature: 
- high optical resolution, 
- scanning in passing light, 
- sufficient scanning field size (min.23x23 cm - typical 
aerial photo size), 
- scanning black and white as well as colour photos, 
- possibility of scanning of a photo made on glass 
plate, and 
- high geometrical similarity of a digital image to a 
original photo. 
The scanners which fulfil all above mentioned conditions 
are very expensive. On market there are also available 
scanners used in printing (designed for printing purpo- 
ses), which are more cheaper. Some technical parame- 
ters like: resolution and size meet the requirements of 
digital photogrammetry but the geometrical quality is 
significantly lower. The UMAX 1200 SE is such type of 
scanner, which is in possession of Department of Photo- 
grammetry and Remote Sensing Informatics, University 
of Mining and Metallurgy, Cracow. 
The goal of this paper is to describe the methodology of 
scanner accuracy testing, to present the results achieved 
and to propose method of geometric calibration of 
scanned images with their accuracy description. 
2. RECORDING AND MEASUREMENT OF TESTED 
DIGITAL IMAGES 
The UMAX 1200 SE scanner, used to gain digital images 
for testing it's geometric accuracy, is a flat type scanner. 
The scanning in a reflected light is possible for a size 
210x300 mm (A4), while in a passing light (for negatives 
20 
and diapositives) is possible for a size 150x220 mm. The 
maximal optical resolution along Y axis (according with 
movement direction of a bar composed of CCD 
elements) equals 1200 dpi while in X direction 600 dpi 
(5000 CCD elements located on a bar, 210 mm long). 
Thus a smallest optical pixel size in Y direction equals 
0,02mm, while in X direction 0,04mm. The maximal 
software scanner resolution is 2400x2400 dpi. It means 
that if decreasing of the pixel size take place, the pixel 
value is interpolated from values of recorded optical 
pixels. Testing the scanning errors was performed for the 
full scanner size (150x220mm) in a passing light. Such 
size make possible to scan 70% of typical air photo size 
23x23 cm. For stereoscoping processing, when only 60% 
of area of each stereo-pair photo is used, such area of a 
scanned photo is sufficient. 
To conduct a geometric calibration of the scanner a 
special pattern was designed and made. The pattern is 
composed of 368 main crosses of size 5x5x0,1mm 
regularly distributed in 10mm intervals and grouped in 16 
columns and 23 rows. Between the crosses located in 
columns 1,2, 8,15 and 16, for further grid densification, 
additional 110 small crosses (size 1x1x0,1mm) were 
located. For the pattern design a programme COREL 
was used. Then the pattern was visualised with resolution 
2400 dpi on LINOTRONIC. The fragment of the pattern is 
shown on Fig.1. 
Pie 
mt 
Fig.1. Fragment of the ideal pattern 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B1. Vienna 1996 
The pe 
stereo 
+3um. 
ideal s 
digital 
The pe 
size 0, 
optima 
Video : 
pattern 
resolut 
Scanni 
minute 
descril 
scanni 
withou 
allowe 
causec 
transp: 
being | 
To elit 
were e 
scanni 
pattern 
patterr 
workin 
to rest 
pattern 
The st 
repeat 
During 
scanne 
Z. Dur 
A...lin 
and in 
The re 
measu 
thousa 
(pixels 
autom 
W.Tro 
progra 
the er 
VSD & 
image. 
coordii 
the dic 
corner 
matior 
For ea 
352 cr 
an enl 
positio 
3.TI 
To det 
the sc 
patter! 
tion) f 
and fu 
pixels) 
given 
deforn