s in resolution has a great influence on the value of a photomap, 
s the interpretation possibilities and the quality of the repro- 
3 4 
C 
tion depend directly on it. 
Reproduction of photomaps 
  
Photomaps in general can be reproduced in three ways: 
(a) on bronide paper 
(b) on ozalid or diazo paper 
(c) with offset printing 
(a) on bromide paper. As we all know, this method of reproduction 
from a negative of the photomap gives the best pos ssible result. 
There is hardly any loss of tone and resolution but this method 
; i dn TO a mie 
is an expensive one and is only usable for a small number of 
copies. 
mi +, : L. hem an Lan YTD 
(b) on ozalid or diazo paper. This is much cheaper than the fore 
going, but the prints, taken from a reversed diapositive, cannot 
maintain their quality because of the bleaching influence by 
daylight. However, many users prefer such diazoprints for quick 
use. 
‘ : se 
i iti : ] uf 1€ ‘oductic che dia- 
No special conditions have to be preset for the preduction of the di: 
positives for printing on diazo continuous tome paper. The continuous 
ve to be a good tone range. .However continuous 
> zopape ich mostly have a matte surface, are not very 
tone diazopapers, whic ÿ ‘ 
p *Y1 A “ha Trt S lZV 2 
popular. Most users prefer a glossy surface and so Lu prints have to 
diazo paper such as the Renker Belipa Kontrast 
  
tone diapo egipiyes,! ha 
be made on contrast x 
paper from Germany or the Regma (French) Contrast paper 153 N. To be 
: = ro 
able to print on such contrast papers one has to screen the photo 
image. The same has to be done when we are 
   
   
f f + c oy i CO C 1i e 
(c) printing a photomap with the offset press where, for best results 
it is recommended to use a very good "white glossy pa Dn 
  
Concerning the density of the screen that one has to use for ue 
duction of a good photomap it has been proved that a density of 70-80 
lines per cm is preferable. The screen dots with such a a density ih 
guarantee a very good tone range without losing quality through print- 
ing difficulties. To screen the photo image a cross line glass screen 
in the copy camera can be used. 
It has been proven (Refer Sweerman 1960) that such a glass screen does 
not enable the attainment of the best tone range in reproduction. To 
get a good result in the middle tone range, one loses ontrast in the 
darkest parts. By varying the distance of the screen to che artes im, 
and the method of illumination, one can influence the result but the 
ideal tone range cannot be obtained. Another disadvantage of the glass 
screen is a loss in resolution by the diffusion of the light as re sult 
of the distance between screen and lith film at the negative plane. To 
over come these difficulties in reproduction techniques contact screens 
were developed especially for the reproduction of continuous tone images 
in half tone reproduction. Such contact screens, like the magenta and 
grey screens with dots of various forms give the opportunity, as Speer 
man shows, to obtain an "ideal" density range. Moreover the contact 
-15- 
  
Screens give a bet 
that here is no di 
and the lith film. 
open the possibili 
Disadvantages are: 
Concerning the las 
contact screen is 
Sweerman (Ref.: Sw 
ideal for tone rep 
Tone reproduction 
image is the same 
both measured with 
About 1960 the Dut 
in cooperation wit! 
Screen. This was 
from black and whi 
in fact it is impo 
Screening of posit 
Noemer 1971) give 
(a) for the scree: 
: positive, one 
(b) for the screen: 
negative, « one 
tween a negat: 
Screen dot.” " 
following exar 
print producec 
both explain : 
detail in the 
In general sci 
a negative sci 
Noemer says "'e 
negative becat 
parts." Howe 
the middle tor 
these importar 
graphical repr 
to apply this 
The results of this 
These are screened 
Aerocarto N.V., the 
Netherlands at Delf 
Screens because 70 
able in the organiz 
no influence on the