GB2150710A

GB2150710A - Copy camera

Info

Publication number: GB2150710A
Application number: GB08430228A
Authority: GB
Inventors: Sven Nygaard
Original assignee: Eskofot AS
Current assignee: Eskofot AS
Priority date: 1983-12-01
Filing date: 1984-11-30
Publication date: 1985-07-03
Also published as: FR2556107A1; NL8403624A; JPS60203947A; DK552983D0; GB8430228D0; DK552983A; GB2150710B; DE3443203A1

Abstract

In a copy camera employing a densitometer 1 and display 6 having a calculating capacity, a correction is effected to take into account internal scattering of light within the material of the sheet bearing the original being copied and absorption of some of the scattered light by the image. <IMAGE>

Description

SPECIFICATION Method and apparatus for determining the ratio of inked area to uninked area on a sheet The invention relates to a method of determining the ratio of inked area to uninked area on a sheet produced by a graphic reproduction apparatus.

According to the invention there is provided a method of determining the ratio of inked area to uninked area on a sheet produced by a graphic reproduction apparatus, in which said areas are measured by reflection of light therefrom, the ratio determined from the measured areas being corrected by a factor (S) dependent upon the material of the sheet.

The method of the invention comprises a correcting of the circumstance that the apparent ratio of inked area to uninked area differs from the actual ratio of inked area to uninked area, said correcting being carried out by slightly reducing the inked area measured to an extent corresponding to a correcting being carried out of the circumstance that part of the light is introduced under an inked area as a consequence of the diffusion in the material, said part of light therefore being unreflective unlike the light hitting the inked area at a distance from the inked areas.

The method of the invention is for instance suitable for use in connection with a developing machine or in connection with a printing machine, where there is interest in knowing the density of the points on a sheet produced.

The invention will now be described by way of example with reference to the drawings, in which Figure 1 illustrates a process-work camera for carrying out the method according to the invention and comprising a densitometer capable of measuring the density of the points on an original; and Figure 2 illustrates the principle according to which the densitometer of Fig. 1 operates.

The invention is to be described in relation to a process-work camera shown in Fig. 1 which comprises a frame which carries a permanent table with a glass plate for a sheet of lightsensitive material. A cover 2 is positioned on the glass plate so as to retain the sheet. A photographic objective is carried by an up and downwardly displaceable bellowS3. A table 4 is positioned below the objective and mounted in two vertical guides. The table 4 is up and downwardly movable, i.e. towards and away from the objective. The table supports a glass plate, on which the original is positioned. Some luminaries 5 arranged on pivotal arms are adapted to expose the original on the table.

When exposing a sectionally inked area, part of the light penetrates the paper where it is diffused and absorbed by the inked area. A measurement of the reflection cannot therefore indicate the exact ratio of the inked and the uninked area. Thus, according to the invention a ratio determined from measured areas is corrected by calculating a corrected ratio A of inked area to uninked area on the basis of the ratio A' of measured inked area to uninked area, the corrected ratio A being calculated from the formula

when the inked area amounts to less than 50% of the total sheet area, and from the formula

when the inked area exceeds 50% of the total sheet area.

Reference is in this connection made to Fig. 2 showing some squares, the strongly solid square having the area 1. Then A is the area of the inking, i.e. a square inside the solid square, whereas A is the length of the side. The length of the side measured is then corrected to allow for light absorption along the side by deducting a correcting size 8 experimentally determinable, or calculated from a known 50% inking area in connection with a measurement of A'.

In the more complicated case where the inked area exceeds 50% of the sheet area, the uninked area is instead calculated. the uninked area beina 1-A'. Then 8 is added to the lenath of the side, i.e. to

and the corrected uninked area is then

Thus,

represents the inked area.

is material-dependent and assumes for instance as far as square areas are concerned a value of about 0.182 at a baryt paper thickness of 0.14 mm and a measuring area of about 6 mm2 as well as a density of points of 1 600 points/cm2.

The equations should, however, be corrected when the dimensions of the inked areas are smaller than the light diffusion in the paper, e.g. in connection with a screen reflection. When small areas are involved, the absorption assumed in the interpretation of the above equations does not take place due to the above formulae condition that the light diffusion is less than the dimension of the inked areas. Furthermore 8 must +0 if the dimensions of the areaO since no correcting is to be performed if the areas are insignificantly small. Therefore, a suitably uniform transition should be provided between the interval, in which the above equations apply, and the limits where the areas are insignificantly small.According to the invention the materialdependent constant 8 is fixed at A' A' - in the event that it would otherwise exceed - corresponding 2 to the case where the inked area is less than 50% of the sheet area, whereas 8 is fixed at

in the event that

would otherwise be less than - corresponding to the case where the inked area exceeds 50% 2 of the sheet area. These approximations turned out to be suitable in practice.

The above ratio multiplied with 100 is also called the point percentage and said percentage is of importance in connection with screen reflection.

The point percentage may for instance be measured by means of a densitometer 1 (Fig. 1) directly communicating with the process-work camera and utilizing a display 6 and the calculating capacity etc. of the latter.

The method according to the invention may also be used in connection with a developing machine, where interest has arisen for an indication of the amount of developing liquid consumed.

The method according to the invention can, of course, also be used in connection with a printing machine and other types of graphic apparatuses for reproduction.

Claims

1. A method of determining the ratio of inked area to uninked area on a sheet produced by a graphic reproduction apparatus, in which said areas are measured by reflection of light therefrom, the ratio determined from the measured areas being corrected by a factor (8) dependent upon the material of the sheet.

2. A method as claimed in Claim 1, in which a corrected ratio A is calculated from a ratio A' determined from the measured areas using an equation:

when the measured inked area is less than the measured uninked area, and using an equation:

when the measured inked area is greater than the measured uninked area.

3. A method as claimed in Claim 2, in which 8 A' is made equal to - when the measured inked area is less than the measured &num;2 inked area, and 8 is made equal to

when the measured inked area is greater than the measured uninked area.

4. Apparatus for use in carrying out a method as claimed in any preceding claim, in which the area measuring is carried out using a densitometer.

5. A method by a graphic apparatus for reproduction such as for instance a process-work camera, whereby it is desired to measure the ratio of an inked area to an uninked area, characterised by a correcting being carried out of the circumstance that the apparent ratio of inked area to uninked area differs from the actual ratio of inked area to uninked area, said correcting being carried out by slightly reducing the inked area measured to an extent corresponding to a correcting being carried out of the circumstance that part of the light is introduced under an inked area as a consequence of the diffusion in the material, said part of light therefore being unreflective unlike the light hitting the uninked area at a distance from the inked areas.

6. A method as claimed in Claim 5, characterised by the width of the inked area being corrected by means of a material-dependent constant 8.

7. A method as claimed in Claim 5 or 6, characterised by calculating a corrected ratio A of inked area to uninked area on the basis of the ratio A' measured of inked area to uninked area, said ratio A being calculated from the formula

provided the inked area amounts to at least less than 50% of the total area, and from the formula

provided the inked area exceeds 50% of the total area.

8. A method as claimed in Claim 6 or 7, characterised by the material-dependent constant 8 of square areas being fixed at about 0. 182.

9. A method as claimed in Claim 6 or 7, characterised by the material-dependent constant depending on the size of the area and being fixed at A A' - in case 6 otherwise should exceed -, the latter applying when inked area 2 2 exceeds 50%, and by the material-dependent constant S being fixed at

when the inked area exceeds 50% in case

S otherwise should become lower than -.

2

10. A graphic apparatus for measuring the ratio of inked area to uninked area at reflection, characterised by a correcting being carried out of the circumstance that the apparent ratio of inked area to uninked area differs from the actual ratio of inked area to uninked area, said correcting being carried out by slightly reducing the inked area measured to an extent corresponding to a correcting being carried out of the circumstance that part of the light is introduced under an inked area as a consequence of the diffusion in the material, said part of light therefore being unreflective unlike the light hitting the uninked area at a distance from the inked areas, the width of the inked area being corrected by means of a material-dependent constant 8.

11. A graphic apparatus as claimed in Claim 10, for use in connection with a densitometer directly communicating with a process-work camera in order to utilize the display, the calculating capacity etc. of the latter.

12. A graphic apparatus as claimed in Claim 10 for use in connection with a developing machine.

13. A graphic apparatus as claimed in Claim 10, for use in connection with a printing machine.

1 4. A graphic apparatus for reproduction substantially as described with reference to the drawings.

1 5. A method of determining the ratio of inked area to uninked area on a sheet produced by a graphic reproduction apparatus, substantially as hereinbefore described with reference to the drawings.