CA1286910E - Colour reproduction process - Google Patents

Abstract

ABSTRACT THIS INVENTION

A method of printing on a sheet member a realistic image of an original, uses two different superimposed impressions with two different colouring media, A first printing plate is created by interposing at least two filters between the original and the film or photoconductive surface, and a second printing plate is created by interposing at least one filter between the original and the film or photoconductive surface. Then, the two printing plates are used to print the different impressions with two different colouring media.

Description

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IMPROVED COLOUR REPRODU_ r_ ON PRO ES,S

This invention relates generally to the printing industry, and has to do particularly with a process for the generation of the plates necessary to permit colour printing, Even more particularly, the present invent:ion sets forth a method of reducing the number of individual plates which need to be made to satisfactorily reproduce a given coloured picture, painting, transparency or the like, , BACKGROUND OF THIS INVENTION

Currently, a process known as the four-colour separation process lS very widely used in the printed reproduction of coloured pictures, transparencies and the like. The four-colour separation proeess is generally responsible for all of the high-quality coloured reproductions in magazines and books, and is also used for some newspaper work as well, ~ -In diseussing the four-eoIour separation proeess, prior art textbooks have often used impreeise and sometimes eonflieting terminology in describing the colours of proeess eomponents. For example, Donald E.

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Cooke in his book "Dramatic Colour by Overprinting", first published in 1955, second revised edition 1974, the autllor speaks of process or lemon yellow, process red or magenta, and process blue. In t1escribin~ an example colour reproduction at pa~e 74H, the two-colour reproduction is described as using magenta and process blue on yellow base, but in the text below the reproduction is said to be using only two colours, magenta and blue, printed on a yel10w base, For an accurate description of the colours involved in -the process of colour separation and colour printing reference is given to John E.~ Cogoli's book "Photo-offset Fundamentals", published~1973 by MacKnight Publishing Company, where a full explanation of colour reproduction~is given in Chapter 10, Accordingly, there are three additlve primary colours blue, red and green, Each of the additive primary colours has its complemen~tary colours; yellow is complementary to blue, cyan is complementary to red and magenta is ;20 complementary to green. Because of their appearance, cyan and magenta have often inaccurately been termed process blue and process re~d; even more inaccurately cyan has been~simply termed blue. It xhould be noted that process red and process blue refer -to two ; ~ .

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~2~369~0 transparent printing inks among the ~our process inks utilized in the colour printing process, i In the most common version Oe the four-colollr sepàration process, the original colour print or transparency is photographed through difEerent filters or scanned by an automatic scanrler as illustrated on page l90 of the textbook by Cogoli above mentioned; to produce di~ferent individual filrns which correspond to the basic colours of the four-colour separation process:
yellow~ ma~enta or process red, cyan or process blue and black. Because the films produced are separation negatives, the filters utilized to draw out these colours from the original havé tints which are the complementary colours of the cDlours being drawn out.

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rhus, a green filter is used to pick out the magenta or process red. a red filter is used to pick out the cyan or process blue, and a blue filter is used to pick out the yellow. A combination of all filters is ideally utilized to pick out the skeleton black, although in some processes t~he black film is made by photographing .
the original in black-and-white film, without any filter.

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:, ~81~9~() Some "fine tuning" or adjustment of the in~ensities of the various colours in the process is made by selecting exposure times and development times. Also, in some instances the final inks used to print the fina]
reproduction can be varied and selected to atta:in certain effects.

From the four pieces of film produced through th:is process, printing plates are ~lade, these bein~
subsequently attached to plate cylinder in a typical printing machine, which is then able to print thé
reproduction.

Generally speaking, the printing industry is of the view that proper reproduction of any photograph or the like requires a our-colour separation process of the kind just described, However, in certain branches of the printing industry t par:iculsrly in newspapers, shopping bags, the YelIow Pages and advertising flyers, the full four-colour separation process represents a considerable expense, sinee it requires the material to be passed through four;printing stations, in order to receive the * Trade Mark : :

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~8~ii9~0 ~our colou~-s. This in turn requires the production of four plates, and the time required to mount thern, adjnst the cooponents, etc, All of this represents a substantial cost factor which, for obvious reasons, it would be o~ advantage to reduce.

There is a two-ink process Eorming part of the prior art, known as duotone. In one version of this process, often called "Fake" duotone, a black and white original (for example a photograph) is first photographed on "Ortho" film through a contact screen to give a screen negative. "Ortho" film is a high contrast film which is not sensitive to the red region of the spectrumO Then, the same screen is rotated through 30 and another screen negative is taken, substantially identical to the first, also on "Ortho" film. The two films are developed to different densities, then are used ~to make plates which are run in tao colours, for example, red and black.

In another version of duotone, often called "Real"
duotone, the original art is already ïn two colours, for example, red and black. The first step is to shoot '~ ~

~6sln "Ortho" film throu~h a grey contac-t screen without any filter. Both the red and the black will be seen by the film, and the result will be a film in which the red and the black are both picked up as black for printing in red. Then, a panchromatic film is e.~posed through a red filter and a grey contact screen. In this arrangement, the film sees only black for printing in black.

The two films, which are negatives, are then used - to make plates which print red and black, respectively.

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It is also known, particularly, in the food advertising area where blue colours are rare, to do a three-colour separation using the standard filters to obtain yellow, magenta or process red and cyan or process blue, and then to print the image using yellow lS ink, red ink and black ink. In other words, the plate mad2 from the cyan or process "blue" film prints in black ink.
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It is further known to mix various colours to produce various other colours, For example, it is known to print a dot matrix of black superimposed on a dot , : : : :
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12869~0 green. It is also known that rnagenta or process red and yellow will combine in the same way to produce orange.
It is further known that yellow and cyan or process blue - will combine to produce various shades of green.

I have now discovered and developed a process for production of separation negatives and printing pla-tes by which to attain strikingly realistic reproduc~ions of an original utilizing only two printing plates inked ~ with only two different non-process colours. Ilowever, ; ~ 10 the process of making these plates does not involve simply one of the known parts of the standard four-colour separation.
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~;~ By way of explaining this, it should be understood ~- that, if a four-colour separation were made to produce ~ 15 four plates intended to print yellow, magenta or process '-- red, cyan or process blue and black, and then if only ~ the yellow and magenta or process red were printed, or .- ,~ .
only the yellow~ ~cyan process blue and black, or an - other combination which was not the full combination of four colours, the resulting prlnt wouid be clearly and definitely unbalanced, and anyone viewing the print ~` would immediately see -the unbalanced nature of the .., ~' ' - : . . .... ~ : . , : , . . , . ~ . , , ~ :
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colours. The print would appear "too reddisll" or "too far into the blue region", or blotchy. The aim of the process which I have developed is to remove the unbalanced nature of a printed reproduction ma~e with only two impressions, and thus two inks, '' GENERAL DESCRIPTION OF TIII.S_INV_NTION

Simply stated, the improvement which I have developed consists in utilizing, for at least one of the two plates~ a combination of two or more of the standard filters utilized in a typical four-colour process. As is ~ell kno~n in the prior art, for example by reference to the above mentioned book by Cogoli, combining two of the standard filters, when performed on a scanner, is accomplished electronically by computin~ from colour information obtained by scanning -the original image aND
analyzing its colour content using the same standard filters. Such computation is similar to that performed ~- for purposes of colour correction as mentioned by Cogoli ; on page 189.
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More particularly, this invention provides a method of printing on a sheet member a realistic image of an :
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~z~9~o original, utilizing two di~ferent superimposed impressions with two different colouring media. The method includes creating a first prin~ing plate by the interposition of at least two filters between the ori~inal and means for recording a first optical image, then creating a second printing plate by the interposition of at least one filter between the origi.nal and means for recording a second optical image.
Then, the first and second plates are used to print the different impressions with two different colouring media.

ln a preferred embodiment, the means for recording the first and second optical images are pieces of photographic film, and t:le colouring media are non-process printing inks.

In another embodiment, the invention provides amethod of preparing a colour separation negative film, for exposing a printing plate for printing a partial printed image of a colour bearing original image with a predeter~ined non-process ink, comprising the steps of:
(a) creating on said separation negative film a first image exhibit~ng a first range of~densities - : .
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~L~86~10 -- I o corresponding to a predetermined sin~;le colour component in said original image; and (b) crea-tin~ on said separation negative film a second irnage exhibiting a second range of densities corresponding to another single colour component in said original image, whereby two such printing plates, when used to print two superposed impressions with two non~process inks of different colour, print an improved printed image, In still another embodiment, the inven-tion provi.des a method of printing on a sheet member a printed image o:E a colour bearing original image, utilizing two different superposed partial printed images each printed with one or two predetermined non-process ink, comprising: (a~ creating a first printing plate bearing printing information corresponding to at least two colour components in said original image; (b) creating a second printing plate bearing printing information corresponding to at least one other colour component in said original image; and (c) using the first and second printing plates to print the superposed partial printed images each with a different one of the two predetermined non~process inks.

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DETAILED D~scRlprrlo~-oF THIS I~VE~TION

This invention will first be described as it relates to the printing 1ndustry, and subsequently as :it relates to the copying industry.

In one embodiment, when used in the photographic reproduction area, the method of this invention involves making two films by exposure to the originalj at least one of the films being made by the interposition of a~
least two filters between the original and the film during exposure. The filters are used sequentially, rather than together at the same time, Tlle second film may be made in the normal way to select out another , colour, utilizing o~nly a single filter. In a more -~ complex version, the second film may also be the result of utilizing two filters sequentially, As an example, consider the problem of printing~a picture of a baby;'s face with blue eyes against a light ; blue background.~

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. , : , ~ 369~0 Let us assume ~hat the first film to be made will be that for the plate intended to print red ink. In order to pick out the red tints, a green filter i.5 first utilized, and this produces a first exposure on the film. Then, in accordance with this invention, a second filter would be utilized. In this example, I would typically utilize a blue fllter to draw out some of the blue~ for example the blue eyes of the baby, by excluding some of the red that is to be printed by this first plate from the eyes of the baby. This would also pick up some of the blue background~ i.e. less red will be printed there as well. However, for this filter I
would adjust the exposures so that the film contained more of the red than the blue (meaning that in the negative, exposure through the green filter is longer and as a result the range of densities reaches high values), in order to clean out the red tone in the blue eyes, while still leaving enough to enhance the contrast.

The second film would be -that intended to make a plate for printing blue ink. In this example, the "blue" film would be exposed only through a red fiIter, :~ . .

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~l2~3691~) red being complementary to cyan ( which is a combinatior o~ blue and green), so that not on]y blue irl the original but also green, if any, would be printed as blue.

Suppose now that the same picture of the baby against a blue background were to be printed on yello~
stock, for example as a telephone advertisement in the Yellow Pages. In this case, one o~ the two inlcs must be black, since the normal "word" advertisements are printed in black. Because the baby's face is predominantely pink or flesh tone, the coloured ink would be non-process red. However, instead oF merely using a green filter, one would use first a green filter to draw out the red tones, and then a blue filter to "fill in" the blue regions, for example the baby's eyes and the back~round by printin~ less red thereat. The blue contribution would be considerably less than the red. Nonethele6s, there would be some ink printed where the original showed blue (the eyes and the background), ~; 20 and therefore the final printed image would be one in which all major components were present. The second ,.
film (lntended to pr~nt black) ~ould be exposed throogh . .
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a r~d ~llter~ to plc~ up the hlue~ ,lnd the ~)lue eyes an(l back~[)und~ so that the addition of black dn~,s ~o the blue areils will ,,lve ~t ihe detall and Lesolu~ion required~

l'his can be compa~ed to an atteml)t to print the sa~.-.e pictuJe of d blue-eyed ~ by against a blue back~round usino only the black and proce~s led or mac,enta films fro~n a stanllald Fonr-colour sepafation, In this lnstaYIce~ the result would be a Elat picl.ure with 1nsufficiellt contrast, In regard to the copyino industry~ -it is well understood that the copying process involves the esTablishment of a latent electrostatic inage on a dru,l:
or plate constituting a photocondllctive sulfclce, following which a coloured "toner'` lS applied to the i~.age-containing poltions of ti-e photoconductive sur~ace~ the electrical attract1on causing the toner to renlain in certain areas alld he relTloved from others, following which the photoconductive surface with the : 20 coner is ~pplled agains-t a sheet of paper which picks up : the toner as an image. Copiers are known which are capable oF colour reproduction. I'hese copiers wnrk on a principle si~ilar to that util~zed in the four--co]our ' .
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3J,() -~epara~ lon pr ocess df~scribed ear l:ier. I~ ne Lv l h.lt I hf' photocollducti~e surtace is l~po~s~d t. h ~ f' e t l. r.' e S
se4ue(ltial1y to lh~ Ori~.Lrl J I, each t i :!1 e thro~,h .
differellt coloured filter. F`ollow~ L eacll exposllre to t~s~,ll)l-ish the elec-rost.ltic image, a colonrell to~le~ Is applied to the surface, ~In(~ the sheet is prl~ted with that p,-lrticular colour, Therl the sllrface l~ c]ec-rled, e~posed agL~ to the next filter, thell the next toner is applied, and the same sheet is agaln prLnte{l with the new colour, This colltinues for all three colours.

It ~ill be evident that the essence of this invention can be applied to the copying industry, by arrangin~ to have the photoconductive surface e~posed through not olle but two (or nlore) filters. I'hese filters ideally would be used sequentially to build up an electrostatic image which is a composite of tile images which would normally be obtained throllgh the two difierent coloured filters. Then this connposite electrostatic image is contacted by the appropriate coloured toner, and the same is printed on the paper sheet.

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~l2~3~910 -- I r) Whl le one t~mbo(l-imellt ot I hi s invellt iOI~ has b~ erl describe(l ~3bovr ~ i t w:i I 1 be evl.derlt to tho:j~ ski I le(l i"
(h~ art thclt chan~es all(l nlc)d:ilicatiol1s may t~c m~ade therelrl withollt depdrtinj~, trom the es~jence oî this invention, as set torth in the appen~lt~cl c:Laims.

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Claims (28)

1. A method of printing on a sheet member a realistic image of an original, utilizing two different superimposed impressions with two different colouring media, comprising:

creating a first printing plate by the interposition of at least two filters between the original and means for recording a first optical image, creating a second printing plate by the interposition of at least one filter between the original and means for recording a second optical image, and using said first and second plates to print the said different impressions with two different colouring media.

2. The method claimed in claim 1, in which each printing plate is a photoconductive surface in a reproduction system using electrostatic images and one or more toners.

3. The method claimed in claim 2 in which the same photoconductive surface is used sequentially to provide the two printing plates.

4. The method claimed in claim 1, in which the two means for recording the first and second optical images are two pieces of negative photographic film exposed through the said filters to the original, and in which the colouring media are non-process printing inks.

5. The method claimed in claim 4, in which the filters are chosen from among the colours: blue, green and red.

6. The method claimed in claim 5, in which the sheet member is white.

7. The method claimed in claim 5, in which the sheet member is coloured.

8. The method claimed in claim 5, in which the sheet member is yellow.

9. The method claimed in claims 4 or 5, in which there are at least two filters interposed, one at a time, between the original and the means for recording the second optical image.

10. The method claimed in claims 6, 7 or 8, in which the film constituting the means for recording the first optical image is first exposed to the original with one of the said two filters interposed, and then exposed to the original with the other of said two filters interposed.

11. The method claimed in claims 1, 4 or 5, in which there are at least two filters interposed, one beside the other, between the original and the means for recording the second optical image.

12. The method claimed in claims 6, 7 or 8, in which the film constituting the means for recording the first optical image is exposed to the original through the two filters indirectly, excluding an arrangement whereby the two filters are arranged one in front of the other.

13. A method of preparing a colour separation negative film, for exposing a printing plate for printing a partial printed image of a colour bearing original image with a predetermined non-process ink, comprising the steps of:

(a) creating on said separation negative film a first image exhibiting a first range of densities corresponding to a predetermined single colour component in said original image; and (b) creating on said separation negative film a second image exhibiting a second range of densities corresponding to another single colour component in said original image, whereby two such printing plates, when used to print two superposed impressions with two non-process inks of different colour, print an improved printed image.

14. The method as defined in claim 13, said first range of densities exhibiting significantly higher densities than said second range of densities.

15. The method as defined in claim 14, said predetermined single colour component selected from the group comprising red and green.

16. The method as defined in claim 13, said another single colour component being blue.

17. The method as defined in claims 13, 14 or 15, wherein steps (a) and (b) are carried out by means of a combined exposure of said separation negative film.

18. The method as defined as claims 13, 14 or 15, wherein steps (a) and (b) are carried out by superposing said first and second images and then exposing said separation negative film.

19. The method as defined in claim 13, said predetermined non-process ink being red, said predetermined single colour component being green, and said another single colour component being blue.

20. The method as defined in claim 13, said predetermined non-process ink being black, said predetermined single colour component being red, and said another single colour component being blue.

21. The method as defined in claims 19 or 20, said two printing plates, when used, print two superposed impressions, a predetermined one in red and the other in black on yellow paper.

22. A method of printing on a sheet member a printed image of a colour bearing original image, utilizing two different superposed partial printed images each printed with one or two predetermined non-process ink, comprising:

(a) creating a first printing plate bearing printing information corresponding to at least two colour components in said original image;

(b) creating a second printing plate bearing printing information corresponding to at least one other colour component in said original image; and (c) using the first and second printing plates to print the superposed partial printed images each with a different one of the two predetermined non-process inks.

23. The method as claimed in claim 20, said at least two colour components being green and blue, and said first printing plate printing non-process red ink.

24. The method as defined in claims 22, or 23, said at Least one other colour component being red, and said printing plate printing non-process black ink.

25. A method of printing on a sheet member a realistic image of an original utilizing two different superimposed impressions with two different colouring media, the method including the steps of creating a first printing plate by the interposition of filter means between the original and a means for recording a first optical image, creating a second printing plate by the interposition of filter means between the original and means for recording a second optical image, and using the first and second plates to print the different impression with two different colouring media, the first printing plate being created by the interposition or at least two different filters between the original and the said means for recording a first optical image, said different filters being adapted to filter out different colours or combinations of colours, characterised in that the contribution to said first optical image obtained utilizing one of said at least two different filters is considerably less than the contribution to said first optical image obtained utilizing the other of said at least two different filters.

26. The method claimed in claim 25, in which the two means for recording the first and second optical images are two pieces of photographic film exposed through the said filters to the original, and in which the colouring media are printing inks.

27. The method claimed in claim 26, in which the film constituting the means for recording the first optical image is first exposed to the original with one of said two filters interposed, and then exposed to the original with the other of said two filters interposed.

28. A method according to claim 25, in which said first plate is used for printing red ink. said other of said at least two filters is green and said one thereof is adapted to draw out some of the blue from the original, and wherein said second printing plate is used for printing with blue ink and said filter means used for recording said second optical image consists of a single filter,