PROCEDURES AND EXPERIENCES ON USING DESKTOP SCANNER FOR 
ORTHOPHOTO PRODUCTION 
M. Mitrovic , Z. Cvijetinovic , D. Mihajlovic 
Faculty of Civil Engineering, Belgrade University, Bulevar Kralja Aleksandra 73, 11000 Belgrade, Serbia and 
Montenegro, - (mitrovic, zeljkoc, draganm)@grf bg.ac.yu 
Commission I, WG 1/2 
Key Words: Production, Algorithms, Scanner, Software, Calibration, Rectification, Accuracy, Photogrammetry 
ABSTRACT: 
Paper presents procedures and experiences on using low cost desktop scanner Epson Expression 1640XL for orthophoto production. 
Complete process of scanning, scanner calibration and removal of systematic distortions of scanned images caused by scanner .is 
developed and tested on several large projects of orthophoto production. Special, user-friendly software is developed for these 
purposes. The software includes algorithm for scanner calibration and estimation of distortions based on statistical analysis by using 
collocation (linear prediction). It is not expected and required from user to have any idea on the structure and distribution of scanner 
errors. These will be determined by the statistical analysis. Therefore, the software usage is not limited to any particular scanner or 
the type and nature of image distortions it introduces. Batch processing of scanned images is also supported with options for saving 
images in various formats and using several resampling types. 
The results presented in paper shows that the procedure is very fast and reliable when geometric accuracy of scanning is concerned. 
The potentials of the developed software and procedure are high. Total costs for the software and the scanner are approximately ten 
times lower than costs for the professional photogrammetric scanner. The geometric accuracy achieved is between 5 and 10pm, 
which is less than one pixel size in highest scanning resolution (1600 DPI). The aspects of the scanner usage at a high production 
rate are also analysed. Finally, recommendations for further improvements of the developed procedures are given. 
1. INTRODUCTION 
The idea of low cost softcopy photogrammetry is present for a 
long time in photogrammetric theory and practice. However, for 
those who wants to start a completely digital photogrammetric 
production there are still large initial investments to be 
expected, especially when software and hardware is concerned. 
If aerial photogrammetry and orthophoto production are 
concerned, one of the most expensive components for those 
who want to cover the whole production line from the very 
beginning is the acquirement of either digital photogrammetric 
sensor or standard photogrammetric camera and a high quality 
photogrammetric scanner. Both of these options require high 
investments. These investments can be reduced substantially by 
choosing another approach. This involves acquirement of 
standard photogrammetric aerial camera and a low cost desktop 
scanner and suitable software and procedures for scanning, 
calibration and rectification of scanned images. The major 
problem that has to be solved is rather poor geometric accuracy 
of most of the desktop scanners available on the market. 
Desktop scanners are basically intended for quite different type 
of users than typical digital photogrammetry users are. So, this 
type of scanners must be somehow checked before using in 
photogrammetry. Several important features define the level of 
desktop scanner exploitation in photogrammetry: 
e scanner type (flatbed or drum), 
e scanning format - minimum 25 cm*25 em, 
e geometric resolution - 800-1600 dpi, 
e radiometric resolution 10 or more bytes per pixel, 
e geometric accuracy 2-15 um, 
e density range from 2.5 D for panchromatic and from 
3.5 for color, 
capability of scanning transparent materials. 
Simple review of technical features of many new A3 desktop 
scanners might lead to the following conclusion: they can 
satisfy many mentioned features except geometric accuracy 
(very often without information about it). 
Radiometric resolution, quality and scanning speed of desktop 
scanners is similar to photogrammetric scanners. Due to the 
strong competition between manufacturers, desktop scanners 
are built on new sensors, electronic devices and scanning 
software with much improved quality. This is the reason why 
the emphasis in this paper was given to the geometric accuracy, 
that is the most sensitive features for desktop scanners. 
Geometric calibration procedure that is usually provided by all 
desktop scanner manufacturers is incomplete or insufficiently 
accurate for digital photogrammetry needs. Supplied technical 
features rarely represent relevant technical features in terms of 
geometric accuracy through tolerance of RMSE or maximal 
positional error. This is the reason why user of desktop scanner 
has to determine the nature of scanner errors by calibration 
process and afterwards to eliminate the most of them. 
It is possible to determine the law of geometric errors spreading 
by multiple scanning and analysis of results of scanning glass 
plate with dense grid points (coordinates of these points are of 
high accuracy in plate’s coordinate system).