CA1221571A - Method of reproducing images with grey values - Google Patents
Method of reproducing images with grey valuesInfo
- Publication number
- CA1221571A CA1221571A CA000452132A CA452132A CA1221571A CA 1221571 A CA1221571 A CA 1221571A CA 000452132 A CA000452132 A CA 000452132A CA 452132 A CA452132 A CA 452132A CA 1221571 A CA1221571 A CA 1221571A
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- Canada
- Prior art keywords
- grey
- dot
- dots
- grey value
- value
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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- Facsimile Image Signal Circuits (AREA)
Abstract
METHOD OF REPRODUCING IMAGES
WITH GREY VALUES
Abstract The invention concerns a method of reproducing images with grey values,using picture elements (PELS) for the different grey values, which are represented by dot patterns with a different distribution and arrangement of the individual dots, characterized in that for each grey value there is a stock of quasi-equivalent grey value pels, and that for representing each grey value of an original to be reproduced, a pel corresponding to this grey value is selected from the associated stock of quasi-equivalent grey value patterns.
WITH GREY VALUES
Abstract The invention concerns a method of reproducing images with grey values,using picture elements (PELS) for the different grey values, which are represented by dot patterns with a different distribution and arrangement of the individual dots, characterized in that for each grey value there is a stock of quasi-equivalent grey value pels, and that for representing each grey value of an original to be reproduced, a pel corresponding to this grey value is selected from the associated stock of quasi-equivalent grey value patterns.
Description
~22157~
~ETHOD OF REPRODUCING I~AGES
WIT~ GREY VALUES
Field Of_The Invention This invention relates to a method of reproducing images with grey values using dot pattern picture ~ ;
elements.
Prior Art The invention concerns a method of reproducing images witll grey values using picture elements (PELS) for different grey values, which are represented by dot patterns with a different distribution and arrangement of the individual dots. For representing grey values, many different methods have become known which have proved more or less successful in simulating the continuously changing grey tones of a natural image.
For this purpose, different quality criteria are desirable, for example, a resolution which is such that the grey, above all the light grey, tones are satisfactorily reproduced, taking into account spatial frequencies, i.e., the lateral dot resolution, and that the uniformity and fidelity achieved are high.
A high resolution and uniformity are particularly desirable in areas with a constant or slowly changing grey tone. For the following reasons, photography is ideal both for the human eye ~and for optical scanning:
The grain, i.e., the dots, in addition to being stochastically distributed, have different sizes. The known grain structure of photographs has the advantage that the totally non-uniform size and the equally non-uniform distribution of the grains prevents the 122157~
1 occurrence of a m~ire pattern if the image is to be scanned or printed at a particular spatial resolution.
Such moire patterns result from raster and scanning frequencies being superimposed upon each other and from the natural frequencies of printers or image screens.
During the scanning of rastered halftone images, such as in newspaper printing, stripes are formed.
There are serious disadvantages of all sys-tems with constant dot addressing, such as those used in lithography or newspaper printing, as well as of simulation methods, such as supercircle, monocircule, and the like.
The most efficient system used for such purposes is MECCA (Multiple Error Correction Computation Algorithm). It is based on the fact that a complex algorithm uses the continuous siqnal Q (x, y), a weighted mean value of previously computed quantization errors, and a print-out reflecting the local image texture, in order to ensure that a dot is printed and displayed with a constant size. This is in contrast with photography or newspaper printing and with the variable dot size supercircle and monocircle methods simulating same.
As will be explained in detail below, both these methods have specific disadvantages. Simulation systems, for example, with a fixed pel size necessitate elaborate programming and storage means.
122~71 1 Summary of the Invention Therefore, it is the object of the invention to provide a method of the previously described kind which supplies a continuous or quasi-continuous grey value scale of almost white to black. In accordance with the invention, this is accomplished in that for each grey value there is a stock of quasi-equivalent grey value pels, and that for representing each grey value of an original to be reproduced, a pel corresponding to this grey value is selected from the associated stock of quasi-equivalent grey value patterns.
Further embodiments of the invention may be seen from the sub-claims.
One way of carrying out the invention wilL be described in detail below with reference to drawings which illustrate only one specific embodiment, in which:
Figs. la and lb show pels with only one of, for example, 16 dots;
Figs. 2a, 2b and 2c show different clusters or dot groups in pels;
Fig. 3 shows the grey stages for a pel with 16 dots;
Fig. 4 shows a pel with four adjacent dots as a cluster;
Fig. 4A shows the relevant grey scale;
'~
r- _ t ~2ZiS~71 l Fig. 5 shows another grey scale and Figs. 5a and 5b sho~ a pel ~lith 1/4 dot;
Figs. 6a - 6e show different pels with 4 dots eachi Figs. 7a and 7b show pels which are quasi-equivalent with respect to their grey value;
Fig. 8 is a diagram representing the dependence of the grey value on the respective pattern, the diameter of the clusters and the diameter of the dots, and Fig. 9 is a block diagram explaining the entire method.
The various disadvantages of the methods known so far will he described below.
According to Figs. la and lb, at a high resolution of, for example, 600 pels per inc~,`~ne such pel consists of a gridlike, preferably square, structure of dots with a spacing d which for 16 individual dots may be of the order of 42.8 ~m. Conceivable for this purpose are grids with 9 dots, 16 dots, 49 dots, 64 dots, etc. For simplicity's sake, it is assumed that there is a gr~d with 16 dots. If all these dots are used to reproduce a pel, a black image is obtained, and if none of the dots is used, the resultant image is white. This shows quite clearly that 16 grey levels can be obtained, ranging from 1 to 15 of 16 possible dots. The smallest--black area obtainable has a blackness of 1/16 = 6.2 %. If, for obtaining the lowest grey value, the individual dot is recurrently arranged at the same point of the grid, then stripe or moiré patterns occur which are highly undesirable.
If, according to Fig. 2, for example, 4, 6, 8, 10, 12 or 14 dots are used from directly adjacent positions arranged one below the other, clusters are formed which have a particular repetition frequency that will detrimentally affect the reproduced image. The grey levels obtained in this case are shown in Fig. 3~ ' . .
.... .
_ ._ lZ21~71 1 There are several possibilities of using these 16 grey levels. Assuming, for example, according to Figs. 4 and 4a, that a pel comprises 4 dots, then the smallest black area has 1/4 or about 25 6 blackness, i.e., at the lowest grey value, the blackness is not less than 25 ~.
If, according to Figs. 5, 5a and ~b, it is assumed that each pel comprises only 1/4 dot, then the smallest pel area is 1/64 of the blackness or 1.6 ~.
In this case, the maximum blackness is 25 ~. Thus, with 16 grey levels, the very light grey tones are quite satisfactorily reproduced, ~ut the blackness is only about 25 ~. This shows that both methods are sub-stantially unsuitable.
Assuming that there are square dots and a grid spacing d equalling the dot si~e with the edge length d, then a maximum of 16 grey levels is obtained in a 16-dot array. Figs. 6a to 6e show that several dot arrays may yield the same quasi-equivalent grey value. Four dots in an array may be arranged, for example, adjacent to each other at the edges or in the center. They may also be arranged diagonally or in rows or in cross form, etc. All these ~rays yield practically the same grey level.
, ,~ .
~owever, irrespective of this, spurious frequencies of the printer, the respective paper and the processing steps used will lead to greatly differing pri,nt results in practice. If, for example, as a result of the printer used, the fourth line always varies in the Y-direction, then only the pattern of Fig. 6d will be insusceptible to this variation. Thus, given the following paramete~s, a fixed size 16-dot array will yield a maximum number of 16 non-redundant grey levels.
1. If the edge length of the dots is less than or equal to the grid spacing, there will be 16 grey levels. If, on the other hand, the edge length of the Z~ts exceeds the grid spacing, then fewer than 16 grey levels will be obtained.
~ETHOD OF REPRODUCING I~AGES
WIT~ GREY VALUES
Field Of_The Invention This invention relates to a method of reproducing images with grey values using dot pattern picture ~ ;
elements.
Prior Art The invention concerns a method of reproducing images witll grey values using picture elements (PELS) for different grey values, which are represented by dot patterns with a different distribution and arrangement of the individual dots. For representing grey values, many different methods have become known which have proved more or less successful in simulating the continuously changing grey tones of a natural image.
For this purpose, different quality criteria are desirable, for example, a resolution which is such that the grey, above all the light grey, tones are satisfactorily reproduced, taking into account spatial frequencies, i.e., the lateral dot resolution, and that the uniformity and fidelity achieved are high.
A high resolution and uniformity are particularly desirable in areas with a constant or slowly changing grey tone. For the following reasons, photography is ideal both for the human eye ~and for optical scanning:
The grain, i.e., the dots, in addition to being stochastically distributed, have different sizes. The known grain structure of photographs has the advantage that the totally non-uniform size and the equally non-uniform distribution of the grains prevents the 122157~
1 occurrence of a m~ire pattern if the image is to be scanned or printed at a particular spatial resolution.
Such moire patterns result from raster and scanning frequencies being superimposed upon each other and from the natural frequencies of printers or image screens.
During the scanning of rastered halftone images, such as in newspaper printing, stripes are formed.
There are serious disadvantages of all sys-tems with constant dot addressing, such as those used in lithography or newspaper printing, as well as of simulation methods, such as supercircle, monocircule, and the like.
The most efficient system used for such purposes is MECCA (Multiple Error Correction Computation Algorithm). It is based on the fact that a complex algorithm uses the continuous siqnal Q (x, y), a weighted mean value of previously computed quantization errors, and a print-out reflecting the local image texture, in order to ensure that a dot is printed and displayed with a constant size. This is in contrast with photography or newspaper printing and with the variable dot size supercircle and monocircle methods simulating same.
As will be explained in detail below, both these methods have specific disadvantages. Simulation systems, for example, with a fixed pel size necessitate elaborate programming and storage means.
122~71 1 Summary of the Invention Therefore, it is the object of the invention to provide a method of the previously described kind which supplies a continuous or quasi-continuous grey value scale of almost white to black. In accordance with the invention, this is accomplished in that for each grey value there is a stock of quasi-equivalent grey value pels, and that for representing each grey value of an original to be reproduced, a pel corresponding to this grey value is selected from the associated stock of quasi-equivalent grey value patterns.
Further embodiments of the invention may be seen from the sub-claims.
One way of carrying out the invention wilL be described in detail below with reference to drawings which illustrate only one specific embodiment, in which:
Figs. la and lb show pels with only one of, for example, 16 dots;
Figs. 2a, 2b and 2c show different clusters or dot groups in pels;
Fig. 3 shows the grey stages for a pel with 16 dots;
Fig. 4 shows a pel with four adjacent dots as a cluster;
Fig. 4A shows the relevant grey scale;
'~
r- _ t ~2ZiS~71 l Fig. 5 shows another grey scale and Figs. 5a and 5b sho~ a pel ~lith 1/4 dot;
Figs. 6a - 6e show different pels with 4 dots eachi Figs. 7a and 7b show pels which are quasi-equivalent with respect to their grey value;
Fig. 8 is a diagram representing the dependence of the grey value on the respective pattern, the diameter of the clusters and the diameter of the dots, and Fig. 9 is a block diagram explaining the entire method.
The various disadvantages of the methods known so far will he described below.
According to Figs. la and lb, at a high resolution of, for example, 600 pels per inc~,`~ne such pel consists of a gridlike, preferably square, structure of dots with a spacing d which for 16 individual dots may be of the order of 42.8 ~m. Conceivable for this purpose are grids with 9 dots, 16 dots, 49 dots, 64 dots, etc. For simplicity's sake, it is assumed that there is a gr~d with 16 dots. If all these dots are used to reproduce a pel, a black image is obtained, and if none of the dots is used, the resultant image is white. This shows quite clearly that 16 grey levels can be obtained, ranging from 1 to 15 of 16 possible dots. The smallest--black area obtainable has a blackness of 1/16 = 6.2 %. If, for obtaining the lowest grey value, the individual dot is recurrently arranged at the same point of the grid, then stripe or moiré patterns occur which are highly undesirable.
If, according to Fig. 2, for example, 4, 6, 8, 10, 12 or 14 dots are used from directly adjacent positions arranged one below the other, clusters are formed which have a particular repetition frequency that will detrimentally affect the reproduced image. The grey levels obtained in this case are shown in Fig. 3~ ' . .
.... .
_ ._ lZ21~71 1 There are several possibilities of using these 16 grey levels. Assuming, for example, according to Figs. 4 and 4a, that a pel comprises 4 dots, then the smallest black area has 1/4 or about 25 6 blackness, i.e., at the lowest grey value, the blackness is not less than 25 ~.
If, according to Figs. 5, 5a and ~b, it is assumed that each pel comprises only 1/4 dot, then the smallest pel area is 1/64 of the blackness or 1.6 ~.
In this case, the maximum blackness is 25 ~. Thus, with 16 grey levels, the very light grey tones are quite satisfactorily reproduced, ~ut the blackness is only about 25 ~. This shows that both methods are sub-stantially unsuitable.
Assuming that there are square dots and a grid spacing d equalling the dot si~e with the edge length d, then a maximum of 16 grey levels is obtained in a 16-dot array. Figs. 6a to 6e show that several dot arrays may yield the same quasi-equivalent grey value. Four dots in an array may be arranged, for example, adjacent to each other at the edges or in the center. They may also be arranged diagonally or in rows or in cross form, etc. All these ~rays yield practically the same grey level.
, ,~ .
~owever, irrespective of this, spurious frequencies of the printer, the respective paper and the processing steps used will lead to greatly differing pri,nt results in practice. If, for example, as a result of the printer used, the fourth line always varies in the Y-direction, then only the pattern of Fig. 6d will be insusceptible to this variation. Thus, given the following paramete~s, a fixed size 16-dot array will yield a maximum number of 16 non-redundant grey levels.
1. If the edge length of the dots is less than or equal to the grid spacing, there will be 16 grey levels. If, on the other hand, the edge length of the Z~ts exceeds the grid spacing, then fewer than 16 grey levels will be obtained.
2. The lightest grey level is the lighter, the smaller the edge length of the dot is. But if the edge length of the dots is less than the grid spacing, ~he full b~ackness will not be obtained. This means . .
GE~-83-021 5 .~.
~i " v lZ2~7~
l that at a fixed dot size t~.e minimum and the maximum grey value and the number of non-redundant grey levels will be equally ixed.
Patterns with the same grey level may be selected SUC}I that the reproduced print is substantially free from defects.
If, for example, the size of the individual dots is varied from one array to another, while it is fixed for the dots in a 16-dot pel, then the advantages explained with reference to the example with 1 dot per pel, 4 dots per pel and 1/-1 dot per pel are obtained.
1. The grey value range can be increased in the afore-mentioned e:cample from 1.6 up to 100 ~ blackness.
2. The number of grey value stages can be increased almost arbitrarily after the desired dot sizes have been chosen.
GE~-83-021 5 .~.
~i " v lZ2~7~
l that at a fixed dot size t~.e minimum and the maximum grey value and the number of non-redundant grey levels will be equally ixed.
Patterns with the same grey level may be selected SUC}I that the reproduced print is substantially free from defects.
If, for example, the size of the individual dots is varied from one array to another, while it is fixed for the dots in a 16-dot pel, then the advantages explained with reference to the example with 1 dot per pel, 4 dots per pel and 1/-1 dot per pel are obtained.
1. The grey value range can be increased in the afore-mentioned e:cample from 1.6 up to 100 ~ blackness.
2. The number of grey value stages can be increased almost arbitrarily after the desired dot sizes have been chosen.
3. The number of suitable patterns for the same grey value is increased considerably.
-) For the purpose of the afore-mentioned examp1e providing for a blackness of25 ~, it is possible, according to Figs. 7a and 7b, to have 4 grid points with 1 dot each or 1 grid point with a cluster of four dots or 16 grid points with 1/4 dot each. If, in addition, patterns of the same grey value, which may be referred to as quasi-equivalent grey value patterns, are mixed in a random generator, the print result or the reproduced image will be largely free from random defects attributable to the printer or the paper. ~efects attributable to the system are largely eliminated by the choice of pattern. By varying the number of dots in the pel array and by varying the dot size from one array to another, the range of possible grey ~) values and their scaling can be increased almost arbitrarily and the susceptibility to defects at higher resolutions be reduced.
By storing the patterns and their associated dot sizes, a grey value entered into the printer can be processed and printed quasi-analogously.
~2~71 l This is the basic concept underlying the invention. By varying the number of the individual dots of a pel and/or their position and/or their cluster and/or their si~e, a vast number of pels with equivalent grey values may be represented. Thus, the invention offers the following substantial advantages:
1. There is an arbitrary number of grey tones for each pel, so that the resolution is subs~tantially higher than that previously obtainable with identical pel sizes.
2. As there is a plurality of patterns for each grey tone, the choice of the most favourable cluster and/or the most favourable dot size is controlled by microcode.
3. As a result, the patterns may be adapted to the characteristics and natural frequencies of the reproduction means used in the subsequent processing steps.
-) For the purpose of the afore-mentioned examp1e providing for a blackness of25 ~, it is possible, according to Figs. 7a and 7b, to have 4 grid points with 1 dot each or 1 grid point with a cluster of four dots or 16 grid points with 1/4 dot each. If, in addition, patterns of the same grey value, which may be referred to as quasi-equivalent grey value patterns, are mixed in a random generator, the print result or the reproduced image will be largely free from random defects attributable to the printer or the paper. ~efects attributable to the system are largely eliminated by the choice of pattern. By varying the number of dots in the pel array and by varying the dot size from one array to another, the range of possible grey ~) values and their scaling can be increased almost arbitrarily and the susceptibility to defects at higher resolutions be reduced.
By storing the patterns and their associated dot sizes, a grey value entered into the printer can be processed and printed quasi-analogously.
~2~71 l This is the basic concept underlying the invention. By varying the number of the individual dots of a pel and/or their position and/or their cluster and/or their si~e, a vast number of pels with equivalent grey values may be represented. Thus, the invention offers the following substantial advantages:
1. There is an arbitrary number of grey tones for each pel, so that the resolution is subs~tantially higher than that previously obtainable with identical pel sizes.
2. As there is a plurality of patterns for each grey tone, the choice of the most favourable cluster and/or the most favourable dot size is controlled by microcode.
3. As a result, the patterns may be adapted to the characteristics and natural frequencies of the reproduction means used in the subsequent processing steps.
4. The savings in software are enormous.
2~ , ~
2~ , ~
5. Detrimental paper and macLine frequencies are taken into account.
Fig. 8 is a diagram showing the dependence of the grey values of the patterns of Figs. 6a, c, d and e on the diameter of the individual dots from the smallest to the largest dot diameter and from the smallest to the largest cluster diameter. The diagram shows how the grey values of the various patterns depend on the dot and the cluster diameters, respectively.
For selecting the patterns for the individual pels, patterns susceptible to all sorts of disturbances have to be determined either empirically or by computation and be sampled out.
Fig. 9 is a block diagram of the new print or reproduction method for image information. Input 1 receives analogue signals of a dot grid from a video pick-up tube and the like. It is, of course, also possible for input 1 to be supplied with digital data. Input 1 is followed by ~l analog-to-, r .
"
{
~;~2157~
1 digital converter ~ whicn is controlled by a clock generator 3. It is essential with this analo~-to-digital converter that the quantization effected is relatively fine. Owing to the inertia of the human eye, a quantization comprising at least 3~ stages is expedient. It is not difficult, however, to have up to 256 quantization stages which, assuming there is an equal nu~ber of grey values, would lead to a grey value scale no longer recognizable by the human eye. This analogue-to-digital converter is followed by a processor, for exa~ple, a microprocessor 4 which is also clock-controlled by clock generator 3. This processor controls the reproduction unit which, in the present case, is an electroerosion printer.
Each grey value thus stored is associated with a grey value in microcode 5.
The microcode may optionally refer to a customer- or user-addressable control unit 6, by means of which the grey value scale stored in microcode 5 may be changed. In such a case, microcode 5 controls the table look-up in a storage 8 containing the dot patterns for the different grey values.
A storage 9 is addressed in a similar marner. This storage serves to accommodate the associated current and voltage values, as the different diameters or sizes of the dots of a pel are obtained by varying their current or voltage values. For selecting the dot patterns stored in storage 8, a-ran~om generator 7 is provided which is also controlled by clock generator 3. In this case, the two storages 8 and 9 control the driver stages 10 which effect the print process. It is assumed that the driver stages apply the associated currents to the electrodes for printing the pels, so ~hat the step in which printing is effected is designated as 11. The new method ensures grey values ranging, for example, from 1.6 to 100 % blackness and an arbitra;rily finely distributed grey scale. It is particularly advantageous that when the analogue signals received are quantized, the maximum amplitude values may be compressed. Similarly, quantization may be effected to a logarithmic scale. The new method improves an image which is coarse-grained per se to such an extent that its grains are no longer recognizable. The new method makes it possible for the first time to obtain image representations that are comparable to photographs taken on a fine-grained film by means of a high-precision lens.
Thus, the new method permits the production of images of photographic 3 J quality, using printing methods employed for transparent foils.
., " , . ~
GE9-83-021 8 i "
.:. 5
Fig. 8 is a diagram showing the dependence of the grey values of the patterns of Figs. 6a, c, d and e on the diameter of the individual dots from the smallest to the largest dot diameter and from the smallest to the largest cluster diameter. The diagram shows how the grey values of the various patterns depend on the dot and the cluster diameters, respectively.
For selecting the patterns for the individual pels, patterns susceptible to all sorts of disturbances have to be determined either empirically or by computation and be sampled out.
Fig. 9 is a block diagram of the new print or reproduction method for image information. Input 1 receives analogue signals of a dot grid from a video pick-up tube and the like. It is, of course, also possible for input 1 to be supplied with digital data. Input 1 is followed by ~l analog-to-, r .
"
{
~;~2157~
1 digital converter ~ whicn is controlled by a clock generator 3. It is essential with this analo~-to-digital converter that the quantization effected is relatively fine. Owing to the inertia of the human eye, a quantization comprising at least 3~ stages is expedient. It is not difficult, however, to have up to 256 quantization stages which, assuming there is an equal nu~ber of grey values, would lead to a grey value scale no longer recognizable by the human eye. This analogue-to-digital converter is followed by a processor, for exa~ple, a microprocessor 4 which is also clock-controlled by clock generator 3. This processor controls the reproduction unit which, in the present case, is an electroerosion printer.
Each grey value thus stored is associated with a grey value in microcode 5.
The microcode may optionally refer to a customer- or user-addressable control unit 6, by means of which the grey value scale stored in microcode 5 may be changed. In such a case, microcode 5 controls the table look-up in a storage 8 containing the dot patterns for the different grey values.
A storage 9 is addressed in a similar marner. This storage serves to accommodate the associated current and voltage values, as the different diameters or sizes of the dots of a pel are obtained by varying their current or voltage values. For selecting the dot patterns stored in storage 8, a-ran~om generator 7 is provided which is also controlled by clock generator 3. In this case, the two storages 8 and 9 control the driver stages 10 which effect the print process. It is assumed that the driver stages apply the associated currents to the electrodes for printing the pels, so ~hat the step in which printing is effected is designated as 11. The new method ensures grey values ranging, for example, from 1.6 to 100 % blackness and an arbitra;rily finely distributed grey scale. It is particularly advantageous that when the analogue signals received are quantized, the maximum amplitude values may be compressed. Similarly, quantization may be effected to a logarithmic scale. The new method improves an image which is coarse-grained per se to such an extent that its grains are no longer recognizable. The new method makes it possible for the first time to obtain image representations that are comparable to photographs taken on a fine-grained film by means of a high-precision lens.
Thus, the new method permits the production of images of photographic 3 J quality, using printing methods employed for transparent foils.
., " , . ~
GE9-83-021 8 i "
.:. 5
Claims (3)
1. A method of reproducing images using dots within an area to represent a grey value, said method comprising:
providing a stock of different dot structures for each desired grey value, each said structure being formed within an area representing a grey value, wherein each dot structure having a similar grey value has a unique dot structure, said unique dot structure being achieved by different arrangement of dots within each structure, and randomly selecting in accordance with a desired grey value a dot structure from said stock of different dot structures.
providing a stock of different dot structures for each desired grey value, each said structure being formed within an area representing a grey value, wherein each dot structure having a similar grey value has a unique dot structure, said unique dot structure being achieved by different arrangement of dots within each structure, and randomly selecting in accordance with a desired grey value a dot structure from said stock of different dot structures.
2. A method as defined in claim 1 wherein said unique dot structures are provided by changing the dot sizes in the different structures in such a manner that a similar percentage of the structure area is covered by the dots for each grey level.
3. A method as defined in claim 1 wherein said unique dot structures are provided by varying the location of the dots within an area while retaining a similar percentage of the total structure area covered by the dots for each grey level.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| EP83104301.3 | 1983-05-02 | ||
| EP83104801A EP0095643B1 (en) | 1982-05-29 | 1983-05-16 | Feeding and tensioning device for a strap to be tensioned around a package |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1221571A true CA1221571A (en) | 1987-05-12 |
Family
ID=8190467
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000452132A Expired CA1221571A (en) | 1983-05-02 | 1984-04-16 | Method of reproducing images with grey values |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1221571A (en) |
-
1984
- 1984-04-16 CA CA000452132A patent/CA1221571A/en not_active Expired
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