Improvements in the Construction of Line Screens for the Production of Half Tones in Photo Printing Processes.
Year: 1894

page_text: Date of Application, 27th Feb., 1894-Accepted, 31st Mar., 1894
COMPLETE SPECIFICATION.
Improvements in the Construction of Line Screens for the
Production of Half Tones in Photo Printing Processes.
I, ROBERT SCHORR of 18 Schiller Street, Gera, in the German Empire,
Chromolithographer, do hereby declare the nature of this invention, and in what
manner the same is to be performed, to be particularly described and ascertained
in and by the following statement :-
This invention relates to the line screens or nets which are employed in the
production of photo process blocks or typographic printing and of transfers for
lithographic work, and in which the half tones and gradations of shade of the
original are desired to be represented. These line screens or nets are at present
produced generally either by taking a negative or photographic print from a plate
engraved with suitable single or double cross lines, or by drawing such lines direct
with a diamond or point upon a glass plate which will take the place of the negative.
The line screen or net so produced is placed in the production of the half
tone picture, in front of the photographic plate upon which the picture is to be
taken. Only the spaces between the lines on the sensitised plate are acted upon
by the light and by this means the picture is divided into large and small dots
which have the form and relationship represented by Figure 1 of the accompanying
drawings. That is to say, the white spaces give a re-production of the original.
By inspection of this figure of the drawings it will be at once seen that the dots
on the diagonal line d and its production, are considerably farther apart than
those lying on the original lines a h, and that for this reason it will be
impossible to obtain exactly true reduced re-productions of the lights and shades
of the original picture.
The principal imperfection of the existing line screen or net system is that
although the high and medium lights may be fairly retained, yet, in the case of
the darker shades, the dots become larger and meet each other more or less
according to the depth of shadow, and of course those which are nearer meet
first. Thus, referring again to Figure 1 of the drawings, the dots will meet
along the lines a h and may not meet along the line d, or, their approach will
be nearer along a h than along d.
My improvements consist in arranging-and-constructing the lines of the screen
or net in such a manner that the dots will be at equal distances from each other,
as represented by Figure 2 of the accompanying drawings. Since these dots i are
all at exactly equal distances apart, it is impossible for them to approach each
other unequally as is the case with the existing systems as already herein described.
The running together of the dots into lines is thus impossible because the dots are
not produced by lines. The shape of the dots is of no consequence whatever and
they may be indifferently triangular square or round, although it may be possible
that in the majority of cases round dots may be preferred.
As already described, the different gradations of shade of the original picture
have to be produced by larger or smaller dots, and as the dots arranged according
to my improved system are all at equal distances from all their neighbours, they
have a wider margin within which to expaud without coalescing, and on this ground
alone the lights and shades of the original are reproduced with greater certainty
and truth than at present.

page_text: Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same. is to be performed, I declare that what I
claim
A screen or net for the photographic reproduction for printing purposes of shaded
pictures, having each dot at an equal distance from all its neighbouring dots,
constructed and arranged substantially as hereinbefore described and as illustrated
by Figure 2 of the accompanying drawings.
Dated this 26th day of February A.D. 1894.
WILLIAM E. HEYS,
Agent for the Applicant.