A RECTIFICATION OF DIGITAL IMAGES OBTAINED FROM AN ANALOGICAL VIDEORECORDING 
Patrizia Midulla 
Researcher - “Città e Territorio” Department, University of Palermo - Italy 
ISPRS - WG VI/3 
KEY WORDS: Digital Photogrammetry, Digital Images, Architectural Survey, Rectification, Video-camera, 
Videorecording. 
ABSTRACT 
This paper describes an easy and low-cost method of surveying buildings by using digital snapshots extrapolated from a 
videorecording and successively rectified. The effectiveness of this method was verified through a case study comprised 
of four different steps. First, filming a building’s facade by using an analogical video camera; second, digital acquisition; 
third rectification through digital software; finally, verification of the precision of the obtained image. The advantages of the 
above method are then discussed. This method is fairly precise and easily applicable, offers the user an inexpensive sur 
vey procedure and comprises a more complete medium, such as videorecording as opposed to photography. 
As a result of the low resolution of analogical filmed images, notwithstanding the above-mentioned advantages, it is advis 
able to limit the use of this method primarily to expeditious survey applications. 
1. INTRODUCTION 
Substantial progress has lately been made in applying dig 
ital technologies to photogrammetry. Progress primarily 
concerns the way photogrammetric operations can be car 
ried out by computers using manual, half-automatic or 
automatic processes. However, innovations also pertain to 
how surveys can be carried out with regard to photo taking 
and image treatment. This paper describes a new applica 
tion in dynamic survey which consisted of shooting a vide 
orecording instead of taking photos, thus using a video 
camera instead of a photo camera. For example, this pro 
cedure can successfully be applied in expeditious survey. 
Videorecordings are constituted by a sequence of frames 
that are viewed at a particularly high speed which allows 
the human eye to perceive the various frames as if they 
formed a moving image. As a result, it is possible to inves 
tigate an object from various points of view continuously. 
Videorecordings are used mainly for the purpose of docu 
mentation; however, they also contain geometrical infor 
mation that can be extracted from the single frames of a 
videorecording, provided that they are turned into digital 
pictures beforehand. This procedure is particularly advan 
tageous in architectural applications. 
This research into the use of ‘videotaping techniques’ 
comprises two phases. The first phase concerns the appli 
cation of videotaping by using analogical videocameras. 
The second phase, yet to be investigated, concerns the 
application of videotaping techniques by using digital 
videocameras. 
This papers illustrates the first phase as described above. 
It includes a method of digital acquisition of images, as 
extracted from a videorecording, by using three different 
programs. In conclusion, the possibility of using the obtained 
images for the purpose of rectification was examined. 
2. Videocameras and Videotapes 
Using a videocamera in an architectural survey is an effec 
tive surveying procedure, in so far as it provides a dynamic 
view of the object and the possibility of zooming. As a 
result, a large number of images are recorded, and among 
them the more useful ones can be singled out. 
An analogical videorecording is stored onto a videocas 
sette through an electronical process: camera image sen 
sors, which are solid-state semiconductors known as 
“charge-coupled devices”, convert light into an electronical 
signal. As a result, no photographic emulsion is used, 
because information are stored on a physical medium. The 
medium can be either a tape with a polyester base and a 
surface of ferric oxide, chromium dioxide, or metal parti 
cles, or else a non linear “hard”or optical disk, in the case 
of digital video. “Video is nothing other than pure voltage: 
its medium is not really space at all but time. (Barbash I., 
Taylor L. 1997). 
Since video tapes do not have to be processed after being 
exposed, one does not have to wait until they get back 
from a laboratory before checking the product of the shooting. 
Video tapes come in different formats. These are mainly: 
VHS, Super-VHS, Hi-8, DV (digital video) and the profes 
sional “Betacam-SP” and M-ll. You can choose between a) 
a camera composed of lens and image sensors, joined 
together with the recorder by a camera cable, b) a cam 
era and a recorder combined into a ‘camcorder’. In the first 
case, you can use one type of camera and change formats 
at the same time, depending on the chosen type of recorder 
Among the different kinds of analogical formats, S-VHS, 
Betacam-SP” and M-ll offer higher quality. Indeed, half 
inch VHS system records a composite signal. “This means 
that each video track contains not only the sync details (for 
picture and sound) but also the luminance (Y) and chromi 
nance (C) information. By contrast, HI-8 and super-VHS 
use what is called “Y/C signal processing.” Although HI-8 
and Super-VHS don’t actually record Yand C channels on 
different tracks, as do true “component” formats like DV 
and betacam SP, they process and output the luminance 
and chrominance information as separate signals, result 
ing in higher image resolution and color quality.” (Barbash 
I., Taylor L. 1997). 
Visual quality of a video is affected by various factors: first, 
the quality of the actual tape (particularly the uniformity of