US3700329A

US3700329A - Radiographic reduction system

Info

Publication number: US3700329A
Application number: US168116A
Authority: US
Inventors: Robert P Mason
Original assignee: Logetronics Inc
Current assignee: AFP ACQUISITION Corp; LOG ETRONICS Inc
Priority date: 1971-08-02
Filing date: 1971-08-02
Publication date: 1972-10-24
Anticipated expiration: 1989-10-24
Also published as: CH556557A; NL149012B; JPS4825523A; JPS5126263B2; BE779564A; GB1354044A; NL7203260A; CA972206A; DE2236863A1; DE2236863B2

Abstract

The density range existing in a reduced-size copy of a radiographic film is linearly compressed by a system employing a combination of electronic unsharp masking cooperating with a dual-gradient record film. Image densities in the original radiograph between a range of 0 and approximately 2.0 are recorded on the higher contrast gradient portion of the record film characteristic, and are subjected to unsharp masking over the range of said higher gradient portion. Image densities in the radiograph in excess of about 2.0 are recorded, without masking, on the lower contrast gradient portion of said record film.

Description

United States Patent Mason Oct. 24, 1972 [54] RADIOGRAPIIIC REDUCTION SYSTEM 3,545,860 12/1970 Hutchins .355/91 72 inventor: Robert P. Mason Alexandria, Va. 1 Primary Examiner-Samuel S. Matthews A ig 8 Eilollics pringfield, Va. Assistant Examiner-Richard L. Moses [22] Filed Aug 2 1971 Attorney-William D. Hall et a1.

[21] Appl. No.: 168,116 [57] ABSTRACT The density range existing in a reduced-size copy of a [52] US. Cl ..355/81, 355/20 ad g p film is linearly compressed y a y m [51] Int. Cl. ..G03b 27/78 p y g a combination of electronic unsharp mask- [58] Field of Search ..355/81 A, 80, 20, 91, 8; s cooperating with a dual-gradient reeerd 96/27 E 44 Image densities in the original radiograph between a range of 0 and approximately 2.0 are recorded on the [56] References Cited higher contrast gradient portion of the record film characteristic, and are subjected to unsharp masking UNITED STATES PATENTS over the range of said higher gradient portion. Image densities in the radiograph in excess of about 2.0 are 3,177,764 4/1965 Akima "325/30 recorded, without masking, on the lower contrast 3,036,497 5/ 1962 False ..3 5/ gradient portion of Sal-d record film 3,340,360 9/1967 Ceho et a] ..'.355/81 X 3,183,766 5/1965 Takasaka et a] ..355/20 8 Clainm, 2 Drawing Figures Va cu u m \4 15 Platen 14W Record Film Light Detector Unsnarp Masking Control Control 4 Circuit To Deflection Ckt.

(Velocity Modulation) Or To Electron Gun(lntensity Modulation) Patented Oct. 24, 1972 3,100,329

Vacuum 4 FIG. i. fi Ll I ka Record Film Light Detector Unsharp Masking 70 Control Control,

Circuit To Deflection Ckt. (Velocity Modulation) Or To Electron Gun(lntensity Modulation) Electronic Printer e 4 idealized 0 Transfer Characteristic 4.0 Original Radioqraph b Densit u w 30 y 20 I l 0%Unsharp Mask Film Base O 2: [00% And Fog /3l Density 1 l 3 I l Exposure Level Oi Relative LoqE' i Intermediate Film Resulting Densities in intermediate Film 20- ti cira c t e r i siic Relative Lag E idealized Record (intermediate) INVENTOR Robert P. Mason ATTORNEY 2 Film Characteristic ,1 RADIOGRAPHIC REDUCTION SYSTEM BACKGROUND OF THE INVENTION Medical and industrial radiographs are presently produced in ever-increasing quantities. Their huge volume has resulted in a number of significant problems at hospitals and other installations generating such radiographs. More particularly, the radiographs are large and heavy, must be filed per patient examination, several to an envelope, and require considerable space for long-term storage and reference. Such storage facilities, e..g., in hospitals, are extremely expensive and, in addition, involve the commitment of major quantities of silver as part of the film emulsions. Access, originating e. g., from patient history number or name, is a time-consuming process; and when an envelope containing radiographs is actually retrieved, the contents are often randomly scrambled, requiring that a. large number of radiographs be examined and carefully evaluated by highly skilled personnel before any desired radiograph can be utilized.

The foregoing problems would be obviated, of course, if a system could be devised capable of economically reducing an original radiograph to a more easily stored form for latter retrieval and examination by a radiologist, particularly if the reduced form were to lend itself to automatic storage and retrieval techniques. However, any such .solution must simultaneously assure that the reduced radiograph possesses sufficient quality and similarity to the original, for each radiograph which may have to be stored, to permit an accurate radiological diagnosis to be made from the stored record; and this vital consideration imposes major problems which have not been solved heretofore.

More particularly, a typical radiographic (X-ray) film normally employs a double emulsion, coated respectively on opposing sides of a transparent film base, to record two superimposed images which, in their composite, can have a density range up to 4.0, Le, a light transmission ratio of 10,000zl. On the other hand, a typical document recording film, e.g., 35 mm. film, which has been used in other environments to store records for rapid access, is normally provided with only a single emulsion coatinghaving a limited brightness acceptance range, such as 100:1. In theory, in order to faithfully reproduce a radiographic image on a conventional single emulsion film, without loss of vital information, for use in a rapid access storage and retrieval system, the 10,000 to 1 brightness range of the original radiograph has to be linearly reduced, or compressed, to a range of about 100 to 1. In other environments (and sometimes even in radiographic environments, see Mooney US. Pat. No. 3,411,905) image contrast has been controlled by the use of so-called unsharp masks and masking techniques. However, these conventional techniques, per se, do not provide a practical solution to the problems described above since it is inconvenient, and would clearly be uneconomical, to make a separate mask for each radiograph, re-registering it with the original to produce an image of controlled contrast, for storage.

In an attempt to achieve some practical technique to reduce radiographs for storage, the prior art has adopted various approaches, none of which has been entirely satisfactory. In one approach suggested heretofore, the so-called negative-positive process," original radiographs have been optically reduced to an intermediate (negative) form using a uniform light source to illuminate the X-ray. Long scale films such as Panatomic-X and Microfile Radiographic films have been employed; and contact positives have been made on duplicating-type films. However, such positives have shown a severely shortened tonal scale, with lack of detail in both high and low density areas. Accordingly, processes of this type find utility, if at all, only with respect to carefully selected radiographic films of limited contrast range, and do not have the general applicability which is necessary for a truly practical system.

Another approach suggested heretofore has involved the so-called direct reversal process. Original radiographs are optically reduced, in accordance with the negative-positive technique described above, onto direct reversal materials which yield a positive as a result of a single exposure step. This technique is, however, subject to the same loss of informational content already described and again, therefore, has only limited applicability.

Various combinations of silver halide, photochromic and phosphor quenching techniques have also been tried. They are generally too complex, in the case of silver halide; too limited in range, in the case of photochromic materials; or too slow, in the case of phosphor quenching, to make them truly practical and economical.

The problems discussed above are compounded by characteristics of the optical systems which are required to produce the reduced intermediate record. Such optical systems typically employ multi-elements which inherently tend to exhibit some light scattering properties even when of the highest quality. Such light scattering tends to degrade the tonal separation of the intermediate image, particularly in those portions of the record corresponding to the most dense (black) portions of the original radiograph. If the reproduction system contemplates, moreover, that the image in the intermediate record is later to be remagnified, either for purposes of obtaining a copy or for projection viewing, additional light scattering and flare problems tend to further degrade the final image with resultant loss of vital information.

' The present invention, recognizing these problems of the prior art, is concerned with the provision of a new radiographic reduction system, capable of producing a faithful reproduction of an original radiograph at reducedsize (e.g., 4 inches by 5 inches, or in a 35 mm format) which lends itself to more convenient storage and automated rapid access techniques; and is particularly directed to the production of such a reduced intermediate image which retains all vital information present in the original radiograph.

SUMMARY OF THE INVENTION The present invention produces the desirable results described above in a radiographic reduction system which combines the characteristics of known unsharp masking apparatuses with the contrast characteristics of special, commercially available, film employed heretofore for other purposes. The record film employed is selected to exhibit, when properly processed,

a dual-gradient contrast characteristic having a relatively low contrast gradient portion and a relatively higher contrast gradient portion. One such film, presently commercially available, is known as Kodak Gravure Copy film, processed under carefully controlled conditions, e.g., for 7 minutes at 680 F. in Kodak D-76 developer. Films of this type, so processed, exhibit a relatively low contrast gradient portion having a gamma slope of approximately 0.5, or ranging from approximately 0.35 to 0.7, and a relatively higher contrast gradient portion having a gamma slope in the range of approximately 1 to 2.

- The special film discussed above is employed, in the present invention, in conjunction with an unsharp masking apparatus which may correspond to one, or combinations, of the systems described in US. Pat. Nos. 2,842,025, 3,036,497 and 3,115,807. More particularly, the unsharp masking apparatus employed may be of the so-called intensity modulation type, as typified by Craig et al US. Pat. No. 3,115,807 for Electronic Masking, or it may be of the so-called velocity modulation type, as typified by Folse US. Pat. No. 3,036,497.

In accordance with the novel approach used in the present invention, a sheet of radiographic film, having an image therein (which, of course, depending upon the nature of the film and the type of image recorded may have a density range varying from up to a value substantially in excess of 2.0, e.g., 3.5 or 4.0) is positioned closely adjacent the face of the light generating means (e.g., a cathode ray tube) forming a portion of the unsharp masking apparatus. Light, preferably in the form of a scanning spot, passes through successive incremental portions of the image in the radiograph and is then transmitted, through an optical system of suitable resolving quality, onto a supported photosensitive record film having the dual-gradient contrast characteristic described previously. The light passing through the radiographic image is monitored by control circuits forming a portion of the aforementioned unsharp masking apparatus; and said control circuits in turn control either the intensity of the light spot or its scanning velocity, to effect unsharp masking of the image over a selected range of image densities which is closely coordinated with the slope of the relatively higher contrast gradient portion of the record film characteristic.

Any image densities in excess of approximately 2.0 in said radiographic film are recorded, unmasked, on the lower contrast gradient portion of the record film characteristic. Any image densities in the radiographic film in the partial range between 0 and approximately 2.0 are recorded, with unsharp marking, on the higher contrast gradient portion of the record film characteristic. In effecting this recording on the higher contrast gradient portion, in conjunction with the unsharp masking effect which has been achieved, the gross contrast gradient of the overall system is linearized to a composite transfer characteristic having a gamma slope corresponding to the slope of the lower contrast gradient portion in said record film. As a result, the total density range in the original film, ranging from 0 to as much as 4.0, is now linearly compressed and recorded on the record film over a total density range of 0 to 2.0.

It must be understood that in making specific reference to densities such as 0, 2.0, 4.0, etc., in the foregoing description, and in the subsequent description and appended claims, the numbers selected are employed as illustrative only, rather than limitative.

The use of these numbers hereinafter, therefore, should be construed in light of the particular characteristics of the radiographic and intermediate record films employed and they are subject to variation as long as the masking percentage employed in the unsharp masking apparatus is properly coordinated to the record film contrast characteristic.

In addition to linearly compressing the gross contrast information in the original radiograph, the system of the present invention can enhance detail over those portions of the density range in which the unsharp masking apparatus is operative. The reasons for this are explained in Craig, US. Pat. No. 2,969,723; and this feature of the invention enables the ratio of detail contrast versus gross contrast existing in the original radiograph to be adjusted with respect to the characteristics of both the intermediate record film and any subsequent reproduction material. Further, by reducing the original image brightness range from as much as 10,000 to l to about l00 to l, the system enables the optical portions thereof to transfer image information without the addition of significant amounts of nonimage forming lens flare" which, of course, has been one of the major problems characterizing prior attempts to record images of such wide dynamic brightness range. In short, the present invention not only achieves the desired reduction and reproduction of information but, in many cases, actually makes it easier for a radiologist or other skilled person to interpret various portions of the image, particularly the very dense portions thereof, by eliminating the need to so-cal1ed hot light such portions during evaluation and/or diagnosis.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an illustrative diagram of a radiographic reduction system constructed in accordance with the present invention; and

FIG. 2 is a graphical representation of the transfer characteristics of the masking system and related record film, illustrating their cooperative effect.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring initially to FIG. 1, a radiographic reduction system constructed in accordance with the present invention comprises, as described earlier, the combination of an unsharp masking system and an intermediate record film having particular contrast characteristics. The unsharp masking system may take various forms, including those of the prior patents identified earlier; but it must be understood that variations may be made in this respect, e.g., rather than employing cathode ray tube light sources, alternative scannable light sources such as lasers could be employed. In the cathode ray tube embodiment illustrated in FIG. 1, a cathode ray tube 10 provides a source of exposure illumination in the form of a scanning spot of light which is directed through a radiograph 11 mounted closely adjacent to the face of the cathode ray tube. Light passing through the radiograph is depicted by broken lines 12 and is imaged, via an optical system 13 of suitable resolution characteristics, on record film 14 having the dual gradient characteristic described previously (and to be described subsequently in reference to FIG. 2).

Record film 14 is preferably retained in place by a vacuum platen 15 which operates to positively position all portions of the record film 14 at points of sharp focus relative to optics 13 and radiograph 11. The record film 14 may take the form of cut sheets which are fed, by an appropriate mechanism (not shown), from a stack of unexposed film located to one side of the platen 15 onto said platen and then transferred to another stack of exposed sheets. Alternatively, the record film 14 may take the form of a supply roll mounted at one side of the platen and operative to feed a length of record film past the platen 15 to a take-up roll. The platen 15 may be stationary or, alternatively, may be mounted for indexing movement in X and/or Y directions if it is desired to record a number of images in side by side relation to one another on a given area of record film 14.

The unsharp masking system, as described in the various patents identified earlier, includes a light detector 16 which is adapted to monitor the light passing through radiograph 11. Light detector 16 is illustrated in FIG. 1 as a photocell, but in normal course can take the form of a photomultiplier tube or other photo detector associated with appropriate fiber optics to permit the light detector 16 to be placed at any convenient location in the entire equipment. The output of light detector 16 operates a control circuit 17 which may take a variety of forms such as have been described in the previously identified patents; and control circuit 17 operates in turn, in dependence upon the amount of light detected at 16, to control the operation of cathode ray tube so as to achieve unsharp masking. More particularly, the output of control circuit 17 can be connected to the electron gun of tube 10 to achieve intensity modulation (see Craig et a], U.S. Pat. No. 3,115,807) or the output of circuit 17 can be used to control the deflection circuits of the cathode ray tube to achieve velocity modulation (as described in Folse U.S. Pat. No. 3,036,497).

For reasons which will appear hereinafter, it is desirable that the control circuit 17 include provision for adjusting the percentage of unsharp masking which is achieved by the overall system. Craig et al, U.S. Pat. No. 3,1 15,807 describes one circuit for achieving this type of adjustment in conjunction with an intensity modulation unsharp masking apparatus. If a velocity modulation apparatus of the type contemplated by Folse U.S. Pat. No. 3,036,497 is employed, control of the percentage of unsharp masking can be achieved by modifying the circuit shown in the Folse patent to include provision for adjusting the input signal supplied to the horizontal (fast) deflection yoke illustrated in that patent. Adjustments of these general types have been diagrammatically illustrated in FIG. 1 at 18. In addition, as will also become apparent from the discussion of FIG. 2, it is important that the film base plus fog density existing in the original radiograph 11 be exposed at a point corresponding to a density of approximately 2.0 on the higher contrast portion of the contrast characteristic of record film 14; and this consideration is achieved by appropriately calibrating the equipment when it is originally set up. It should further be understood that, in referring to various prior patents as typifying the types of unsharp masking apparatus which can be employed, the actual disclosures of those prior patents include numerous features which may not be necessary in the practice of the present invention; and therefore the unsharp masking equipment actually employed herein can, in many cases, be much simpler than has actually been described in said prior patents, i.e., many features which have been described in those earlier patents can be eliminated in the present system.

The unsharp masking apparatus diagrammatically illustrated in FIG. 1, in the particular application illustrated in FIG. 2, is depicted as operating, in cooperation with the higher contrast gradient portion of record film 14, over a density range of 2.0 to 1.0. In this particular range, the transfer characteristic of the unsharp masking apparatus 10, l618 cooperates with the transfer characteristic of the higher contrast gradient portion of the record film 14 to produce a net transfer characteristic which has a new slope that is effectively a linear extension of the lower contrast portion of the record film gradient. This will become more readily apparent by reference to FIG. 2.

In FIG. 2, four curves are illustrated to depict various different characteristics of different portions of the overall system. Curve 20 illustrates a range of densities which can be found in original radiograph 1 1. The term idealized radiograph has been employed in FIG. 2 since, as will be appreciated by those skilled in the art, curve 20 (and curve 40 to be described) do not include the shoulder and toe portions which are characteristic of all photographic materials. A point 21 on curve 20 (designated by the intersection of broken line e with said curve 20) is intended to represent the inherent density which is always present in the radiographic material, reflecting the film base as well as the fog density resulting, for example, from processing of the film; and all image densities which are present in the radiograph are superimposed on this minimum density value, between point 21 and a density value which may be as high as 3.5 or 4.0. Curve 20 is depicted as substantially linear; and, for the reasons already described, it is necessary, in order to avoid loss of vital image information, to preserve substantial linearity in any intermediate record, copy, or projected image made from the radiograph 1 1.

FIG. 2 further includes a curve 30 which depicts the transfer characteristic of an electronic printer (or unsharp masking apparatus) of one of the types described earlier. As shown by curve 30, the electronic printer is capable of achieving unsharp masking over a range of densities between 0.0 and about 2.0 in the original radiograph. In this particular range, and by ad justment of control 18, the actual percentage of unsharp masking can be varied between 0 percent (depicted at 31) and values approaching percent (depicted at 32). Actually, the percentage of unsharp masking should be adjusted to some value intermediate 0 percent and 100 percent, with the actual adjustment being dependent upon the gamma slope of the higher contrast portion of the record film l4 characteristic. In the particular embodiment illustrated in FIG. 2, it has been assumed that the percentage of unsharp masking has been adjusted to 50 percent as designated at 33.

For density values in excess of about 2.0 in the original radiograph (designated by the intersection of curve 30 with

curves

21, 32 and 33) the unsharp maskin g apparatus merely acts as a conventional light source operating to transmit a fixed and predetermined amount of light through the radiograph in the density range 2.0 to 4.0. This is characteristic of the cathode ray tube unsharp masking systems described in the prior patents identified earlier, and is highly desirable for the present application. It must be understood that, in other systems where this particular characteristic may not occur, e.g., in laser systems where the contrast of the light source may be much greater than in practical cathode ray tube systems, some provision should be included to establish an appropriate break point at which unsharp masking is to commence, e.g., at a density of approximately 2.0 in the original radiograph.

Curve 40 in FIG. 2 depicts the idealized dualgradient contrast characteristic of record film 14. One possible film exhibiting such a contrast characteristic has already been identified. Characteristic curve 40 includes a lower portion which exhibits a relatively low contrast gradient having a gamma slope of approximately 0.5 (as depicted in FIG. 2) and an upper portion having a higher contrast gradient which may have a gamma slope of 1.0 to 2.0. The actual slopes of these different portions of the characteristic curve depend upon the film selected and the processing conditions to which it is later subjected; and in practical embodiments of the present invention which have been successfully employed, the lower portion of the curve has exhibited slopes ranging from 0.35 to 0.7, whereas the upper portion of the curve has exhibited slopes of ap proximately 1.0 and higher, e.g., slopes in the range of 1.0 to 2.0.

FIG. 2 includes a fourth curve, designated 50, which depicts the resultant densities achieved in the intermediate film 14 due to the net transfer characteristic produced by the combined effects of the dual-gradient material 14 and the unsharp masking effect achieved by the electronic exposing apparatus. As will be seen, curve 50 is substantially linear and has a gamma slope of approximately 0.5 throughout. The lower portion of curve 50, between record film densities of 0.0 and 1.0, corresponds to the slope of the relatively low contrast gradient portion of intermediate film l4, and the upper portion of curve 50, between record film densities of 1.0 and 2.0, represents the net or composite effect achieved by the higher contrast gradient portion of the intermediate film 14 when modified by the addition of unsharp masking.

In order that the foregoing may be more fully understood, a number of broken lines a-e, inclusive, have been included in FIG. 2, extending between corresponding points on

curves

20, 30, 40, and 50. Broken lines a, b, and correspond respectively to densities of 4.0, 3.0 and 2.0 in the original radiograph and, as illustrated by the intersection of these three lines a-c with curve 30, images having densities in the range 2.0 to 4.0 in the original radiograph are not subject to any unsharp masking and are exposed on the relatively low contrast gradient portion of intermediate or record film 14 in the density range of approximately 0 to 1.0 in said record film. Broken lines a, b, 0, when traced successively between

curves

20, 30, 40 and 50 indicate, in effect, that image densities in the original radiograph,

between the values 2.0 and 4.0, are recorded on the record film 14 in the range of densities between 0.0 and 1.0, and this, in effect, achieves a linear compression of this portion of the density range in the original radiograph due simply to the characteristic of the lower contrast gradient portion of record film 14 (when suitably processed).

Broken line d is intended to depict any typical density in the range between point 21 (identified earlier) and a density of approximately 2.0 in the original radiograph. lmages having densities in this range are subjected to unsharp masking and, in addition, are recorded on the higher contrast gradient portion of the record film characteristic. More particularly, if line d is traced from curve 20 to curve 33 (representing the assumed transfer characteristic of an electronic printer adjusted to achieve 50 percent unsharp masking), and then downwardly to curve 40, it will be seen that densities corresponding to broken line d are subject to both unsharp masking and to the effect of the higher contrast gradient portion of the record film 14. This achieves enhancement of image detail versus gross contrast within this range and, moreover, as illustrated when broken line d is traced from curve 40 to curve 50, causes the gross contrast information to be recorded along a portion of the net transfer characteristic which constitutes a substantially linear extension of the lower portion of curve 40. In FIG. 2, line at illustrates, in effect, that an assumed density of 1.0 in the original radiograph is recorded in the intermediate film 14 at a density somewhere between 1.0 and 2.0. Similarly, any image densities in the radiograph between the partial range of approximately 0 and 2.0 are recorded on the higher contrast gradient portion of the record film characteristic and manifest themselves, in a net transfer characteristic, as recorded densities between L0 and 2.0 (see curve 50).

Broken line e, as mentioned earlier, represents the minimum density 21 which is always present in the radiograph due to the density of the film base and development fog. The exposure of densities at this minimum level 21 (broken line e) should be so adjusted, by calibration of the electronic printer control circuit 17, that they are recorded at a density of approximately 2.0 on the higher contrast gradient portion of the record film 14. This determines the maximum density which will exist in the record film 14 and assures that no radiographic information will be lost due to underexposure of record film 14.

It must be understood, of course, that the image produced in the record film is of reverse polarity to that in radiograph 11, i.e., it is what has sometimes been termed a black-bones image. Such images are not acceptable to many radiologists for viewing; and therefore the record film 14 is actually an intermediate" film which is used to produce a final copy or other reproduction which is of acceptable polarity. Nevertheless, the intermediate film can be used for purposes of storing the radiograph in reduced form, and for obtaining rapid access thereto; and such films are less likely to be removed from the files since they are themselves of unacceptable image polarity. Copies, of acceptable polarity, can be made from the intermediate film on any film or paper of suitable brightness acceptance range; and paper copies, in particular, may be made rapidly and inexpensively for relatively wide scale distribution if desired, e.g., as a teaching adjunct or for use by a plurality of facilities that may have cognizance of a particular patient.

While I have thus described the preferred embodiment of the present invention, many variations will be suggested to those skilled in the art. Some of these variations have already been described, but others will become apparent from the foregoing description. For example, while the specification refers to radiographs as exposed X-ray films, the present invention is equally applicable to other imaging situations wherein it may be necessary or desirable to linearly compress a relatively wide total image density range to a narrower image density range; and terms such as radiograph" appearing in the specification and claims are intended to be generic to all such situations. It must therefore be understood that the foregoing description is intended to be illustrative only and not limitative of the present invention; and all such variations as are in accord with the principles described are meant to fall within the scope of the appended claims.

Having thus described my invention, 1 claim:

1. A radiographic reduction system comprising means for supporting a photosensitive record film having a dual-gradient contrast characteristic exhibiting a relatively low contrast gradient portion and a relatively higher contrast gradient portion, an unsharp masking apparatus comprising means for generating a moving spot of light, a sheet of radiographic film having an image thereon the density range of which may be as great as 0.0 to 4.0, said radiographic film sheet being supported between said light generating means and said record film, optical means disposed in the light transmission path between said sheet of radiographic film and said record film for producing, at said record film, a reduced size image of the image in said radiographic film as said moving spot passes successively through all incremental portions of said radiographic film image, said unsharp masking apparatus being calibrated to record the film base plus fog density, in said radiographic film sheet, on said record film at a density of approximately 2.0, any image densities in said radiographic film between the partial range of about 0 to approximately 2.0 being recorded on the higher contrast gradient portion said record film characteristic, control means for monitoring the amount of light which has passed through said radiographic film and including means operative to control said moving spot of light to effect unsharp masking of said radiographic film image over said partial range, any image densities in excess of approximately 2.0. in said radiographic film being recorded on the lower contrast gradient portion of said record film characteristic.

2. The system of claim 1 wherein the relatively low contrast gradient portion of said record film has a gamma slope of approximately 0.5, said relatively higher contrast gradient portion having a gamma slope of approximately 1.0.

3. The system of claim 1 wherein the relatively low contrast gradient portion of said record film has a gamma slope in the range of approximately 0.35 to 0.7, said relatively higher contrast gradient portion having a ing means comprises a cathode ray tube including means for scanning an electron beam over the face thereof.

5. The system of claim 4 wherein said control'means comprises means operative to vary the intensity of said electron beam.

6. The system of claim 4 wherein said control means comprises means operative to vary the scanning velocity of said electron beam.

7. The system of claim 1 wherein said means for supporting said record film comprises a vacuum platen.

8. The system of claim 1 wherein said unsharp masking apparatus includes means for adjusting the percentage of masking effected thereby.

Claims

1. A radiographic reduction system comprising means for supporting a photosensitive record film having a dual-gradient contrast characteristic exhibiting a relatively low contrast gradient portion and a relatively higher contrast gradient portion, an unsharp masking apparatus comprising means for generating a moving spot of light, a sheet of radiographic film having an image thereon the density range of which may be as great as 0.0 to 4.0, said radiographic film sheet being supported between said light generating means and said record film, optical means disposed in the light transmission path between said sheet of radiographic film and said record film for producing, at said record film, a reduced size image of the image in said radiographic film as said moving spot passes successively through all incremental portions of said radiographic film image, said unsharp masking apparatus being calibrated to record the film base plus fog density, in said radiographic film sheet, on said record film at a density of approximately 2.0, any image densities in said radiographic film between the partial range of about 0 to approximately 2.0 being recorded on the higher contrast gradient portion said record film characteristic, control means for monitoring the amount of light which has passed through said radiographic film and including means operative to control said moving spot of light to effect unsharp masking of said radiographic film image over said partial range, any image densities in excess of approximately 2.0 in said radiographic film being recorded on the lower contrast gradient portion of said record film characteristic.

3. The system of claim 1 wherein the relatively low contrast gradient portion of said record film has a gamma slope in the range of approximately 0.35 to 0.7, said relatively higher contrast gradient portion having a gamma slope in the range of approximately 1.0 to 2.0.

4. The system of claim 1 wherein said light generating means comprises a cathode ray tube including means for scanning an electron beam over the face thereof.

5. The system of claim 4 wherein said control means comprises means operative to vary the intensity of said electron beam.