GB1566263A

GB1566263A - Measuring optical characteristic

Info

Publication number: GB1566263A
Application number: GB38956/76A
Authority: GB
Original assignee: Toppan Printing Co Ltd
Current assignee: Toppan Inc
Priority date: 1975-09-22
Filing date: 1976-09-20
Publication date: 1980-04-30
Also published as: DE2642647C2; DE2642647A1

Description

(54) IMPROVEMENTS IN OR RELATING TO MEASURING OPTICAL CHARACTERISTIC (71) We, TOPPAN PRINTING CO.

LTD, a company of Japan, of 5-1, Taito 1-chome, Taito-ku, Tokyo, Japan, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to a measuring device for, and to a method of, measuring an optical characteristic of an object and is particularly applicable for colour plate-making.

When a graduated colour image such as a colour picture is printed, it is necessary to measure the optical densities of colour components such as yellows (Y), magenta (M), cyan (C) and black (Bl) of the original picture and especially the optical densities in highlight and shadow portions must be accurately measured in order to determine the working conditions for the colour separation in platemaking.

Even though the measurement of the optical density in a white highlight portion with the conventional densitometer is relatively easy, when the original picture has no white highlight portion, the setting of highlight level in plate-making is somewhat difficult. Furthermore, when the maximum and minimum densities are measured according to the conventional method, it is necessary that several highlight and shadow portions in an original picture are checked with the naked eye, all the densities of such portions measured and the resultant values of densities compared together so as to determine the maximum and minimum values. This procedure takes much labour and is troublesome.

According to a first aspect of the present invention there is provided a measuring device for measuring an optical characteristic of an object, which measuring device comprises scanning means for scanning an object to produce an optical characteristic signal relating to an optical characteristic of the scanned object, display means responsive to the optical characteristic signal for displaying the optical characteristic signal in graphic form and marker signal generating means responsive to the scanning means and independent of the optical characteristic signal for generating a signal to produce on the display means a plurality of calibration markers indicative of values of the optical characteristic to be measured and in a predetermined relationship to the optical characteristic signal so that the measurement of the displayed optical characteristic signal can be read directly from the display means by visually determining the relative position of the, or part of the, optical characteristic signal in relation to the calibration markers.

According to a second aspect of the present invention there is provided a measuring device for measuring an optical characteristic of a subsection of an object, which measuring device comprises scanning means for scanning an object to produce an optical characteristic signal relating to an optical characteristic of the scanned object, identification signal deriving means responsive to the scanning means for deriving an identification signal to identify a subsection to be measured of the object, display means responsive to the optical characteristic signal for displaying at least a portion of the optical characteristic signal in graphic form, marker signal generating means responsive to the scanning means and independent of the optical characteristic signal for generating a signal to produce on the display means a plurality of calibration markers indicative of values of the optical characteristic to be measured and in a predetermined relationship to the optical characteristic signal and gate means responsive to the optical characteristic signal and rendered effective by the identification signal for enabling the display means to display only that portion of the optical characteristic signal corresponding to the optical characteristic of the subsection of the object identified by the identification signal so that the measurement of the optical characteristic of the identified subsection can be read directly from the display means by visually determining the relative position of the, or part of the, optical characteristic signal in relation to the calibration markers.

According to a third aspect of the present invention there is provided a method of measuring an optical characteristic of an object, which method comprises scanning an object to produce an optical characteristic signal relating to an optical characteristic of the scanned object, generating a signal for producing a plurality of calibration markers indicative of values of the optical characteristic to be measured and displaying in graphic form on display means the optical characteristic signal and the plurality of calibration markers, the plurality of calibration markers being displayed in a predetermined relationship with respect to the optical characteristic signal so that the measurement of the displayed optical characteristic signal can be read directly from the display means by visually determining the relative position of the, or part of the, optical characteristic signal in relation to the calibration markers.

A preferred embodiment of the present invention provides an improved density measuring device, with which the maximum and minimum densities can be easily and quickly measured and, in addition, the density of a desired portion can also be measured or compared with the densities of other portions.

A preferred embodiment of the present invention can enable the provision of a measuring device which indicates directly the data of optical densities, as well as a measuring device which can be applied to or incorporates a colour proof or proof viewing apparatus.

A preferred embodiment of a measuring device according to the present invention is used so that an original picture to be measured is scanned by the scanning means such as a television camera to obtain electrical signals of the original picture, the signals are then converted into secondary electrical signals corresponding to the optical density of the original picture by means of a logarithmic converting circuit, the calibration signals generated by the marker signal generating means are added to the secondary electric signals, and the thusobtained combined signal is displayed on the display means which is a wave-form monitor, such as an oscilloscope. The combination of a flying spot scanner and a photo-electric transducer, or optical scanning device with multicolour separating means, may also be used as the scanning means. Further, electrical signals obtained by scanning with a colour proof apparatus can be electronically processed using an embodiment measuring device in accordance with the present invention. If desired the optical density of a desired portion in an original picture can be measured using an embodiment of a measuring device of the present invention.

Advantageously, in the device of the first aspect the optical characteristic signal produced in use, by the scanning means includes a retrace blanking interval, the marker signal generating means generates, in use, the signal for producing calibration markers during the retrace blanking interval and includes means for adding the signal for producing calibration markers to the optical characteristic signal to produce a combined signal and the display means is responsive to the combined signal to display the combined signal in graphic form on the display means. Advantageously, in the device of the second aspect the optical characteristic signal produced, in use, by the scanning means includes a retrace blanking interval, the marker signal generating means generates, in use, the signal for producing calibration markers during the retrace blanking interval and includes means for adding the signal for producing calibration markers to the optical characteristic signal to produce a combined signal and the gate means is responsive to the combined signal so that the calibration markers and the portion of the optical characteristic signal enabled to be displayed by the gate means are displayed, in use, on the display means.

For a better understanding of the present invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 shows a block diagram of a densitometer of the prior art, Figure 2 shows a block diagram of a first embodiment of density measuring device in accordance with the present invention, Figures 3A and 3B show explanatory drawings of wave-forms in the density measuring device of Figure 2, Figure 4 shows an explanatory view of density calibration signals in another embodiment of the present invention, Figure 5 shows a block diagram of a second embodiment of density measuring device in accordance with the present invention, in which a flying spot scanner is used as a scanning device, Figure 6 shows a block diagram of a third embodiment of density measuring device in accordance with the present invention, in which three colour separation is carried out in the scanning step, Figure 7 shows a block diagram of a fourth embodiment of a density measuring device in accordance with the present invention as applied to a colour proofing apparatus, and Figures 8A and 8B show schematic views of images of a colour monitor and of a wave-form monitor as shown in Figure 7.

For the better understanding of the present invention, a densitometer of the conventional art will be firstly described with reference to Figure 1. In the block diagram shown in Figure 1, there are represented a light source 11, an original colour picture 12 to be measured, a colour filter 13, an aperture 14, a photoelectro transducer 15, a logarithmic converting circuit 16 and a meter 17.

In the measurement of an optical density of the original picture 12, it is firstly lit by turning on the light source 11 and the light beams transmitted through the original picture 12 are then filtered by the colour separation filter 13 so as to obtain one primary colour light through the filter 13. The thus-obtained primary colour light to be measured is introduced into the photo-electro transducer 15 by way of the aperture 14 and the light is converted into electrical signals by the transducer 15. Incidentally, the relation between a rate of trans mission (transmissibility) T and an optical den sity D is represented by the following equation: D=log10 (1/T) The photoelectrically-obtained signal is then subjected to logarithmic conversion by the logarithmic converting circuit 16 and it is then indicated on the meter 17.

When an original colour picture 12 has white highlight portions, the setting of the highlight level can be carried out relatively easily since the optical density of one of such portions can be taken as the standard for obtaining separation films in plate-making. However, in the case that the original colour picture has no white highlight portion, the highlight level is set by measuring the optical density of the colour complementary to the lightest colour in the original picture. Unfortunately, several difficulties and troubles occur.

Furthermore, when the highest optical density is measured with regard to an original picture comprising various optical density portions, some points of the high density portions on the picture must be checked with the naked eye and they are moved below the aperture 14 so as to obtain the value of the highest density, which is also applied to the measurement of the lowest density. Therefore, it has been difficult with the prior art to measure the optical densities in original colour pictures and much labour has been required for such measurement, which is also troublesome.

Figure 2 shows a block diagram of a first embodiment of density measuring device in accordance with the present invention, in which a television camera 23 (hereinafter referred to as "TV camera"), a wave-form monitor 25 such as an oscilloscope and a calibration signal generator 26 are shown.

Other numerals indicate the same means as those in the above-mentioned Figure 1, respectively.

In the measurement of the optical density of the original picture 12, the light source 11 is turned on to light up the original picture 12 and the image of transmitted light passes through the filter 13 and then to the TV camera 23 in which the image is scanned with electron beams so as to convert it into electrical signals. These photoelectrically converted signals are further converted into other electrical signals that correspond to the density by using the logarithmic converting circuit 16.

Meanwhile, calibration signals are produced by the calibration signal generator 26 and the signals are added in the retrace blanking interval of the former electrical signals in such manner that the maximum level of the electrical signals coincide with the zero value of the calibration signals. Thus, combined signals are then displayed on the wave-form monitor 25.

In the density measuring device shown by the block diagram of Figure 2, the transmitted light through the original transparent picture 12 is measured; however, when the reflected light from an original reflection picture is measured, the picture 12 may be lit by a light source 11 placed on the opposite side compared with the side shown in Figure 2, and the reflected light is caught by the TV camera 23.

After that, the same measures as in the above case can be taken so as to produce the waveform image on the wave-form monitor 25.

Figures 3A and 3B show explanatory illustrations of wave-forms obtained with the device shown in Figure 2 in which the selected scanning line 32, the obtained electrical signal 33, the electrical signals 34 and 37 after the logarithmic conversion and optical density calibration signals 35 are shown.

In Figure 3A, the electrical signal 33 is obtained by scanning an original picture 12 with a selected single scanning line 32. According to the intensity of transmitted light through the original picture 12, the value of the electrical signal 33 is varied, that is, the electrical signal 33 corresponding to highlight portions is high, on the other hand, the electrical signal in shadow portion is low. The relation between a rate of transmission T and an optical density D is represented by the following equation: D=log10 (1/T) Therefore, the electrical signal 33 is then subjected to logarithmic conversion in accord dance with the above equation to obtain the electrical signal 34 after the logarithmic conversion. In this example, the calibration signals 35 to be indicated on the wave-form monitor 25 are arranged at regular intervals and in correspondence with the densities. The calibration signals 35 such as stepped waves are combined with the vertical or horizontal retrace blanking interval of the above electrical signals 34 and they are simultaneously displayed on the wave-form monitor 25. With these calibration signals 35, the optical densities in several portions at the scanning line 32 on the original picture 12 can be directly read out. In Figure 3A, the displayed pattern shows the state of a selected single scanning line 32. When the original picture 12 is totally scanned by the TV camera 23 with a plurality of scanning lines and the obtained electrical signals are logarithmically converted, the resultant signals 37 after the conversion can be represented by an area having widths (optical density ranges) as shown in Figure 3B. Therefore, by using this embodiment density measuring device of the present invention, the maximum and minimum optical densities of the original picture as well as the optical density of every portion of the original picture 12 can be quite easily measured.

As disclosed above, the density calibration signals 35 are arranged at regular intervals from the maximum density of 3.0 to the minimum density of 0 in the above embodiment as shown in Figures 3A and 3B. However, it is important to measure the optical density of each primary colour in the highlight portion as accurately as possible in practical plate-making. Accordingly, in the embodiment shown in Figure 4, the density calibration signals 38 in the low density range are further subdivided. In this embodiment, the density calibration signals 38 are indicated at intervals of 0.1 in the range from 0 to 1.0 and 0.5 in the range from 1.0 to 3.0.

In the above-disclosed two embodiments, the density calibration signals 35 and 38 are displayed in horizontal lines; however, they can be arranged in step-like forms, if desired.

A second embodiment of the density measuring device in accordance with the present invention is shown in Figure 5, in which the numeral 39 denotes a flying spot scanner and other numerals represent the same as those shown in Figures 1 and 2.

In the flying spot scanner, a moving spot of light controlled mechanically or electrically scans the image field and the light reflected from or transmitted through the image field is picked up by a photo-electro transducer to generate electric signals. In this embodiment, the original picture 12 is scanned by the optical beam from the flying spot scanner 39, and the transmitted light passes through the filter 13 to the photo-electro transducer 15 to be transduced into electrical signals. The procedure after this is the same as that of the above embodiment shown in Figure 2.

In Figure 6, there is shown a third embodiment of the density measuring device in accordance with the present invention, in which a three-colour optical separation system 44, TV cameras 45 to 47, exclusive for R (red), G (green) and B (blue), respectively, adders 48, 49 and 50 and a parallel-series converter 51 are shown. Other numerals represent the same as those in Figures 1 and 2.

In operation, the original picture 12 is lit by turning on the light source 11 and the transmitted light through the original picture 12 is then separated into R (red), G (green) and B (blue) by the three-colour optical separation system 44. The thus-obtained threecolour separated images are formed in the TV cameras 45 to 47 of R, G and B and, at the same time, the images are converted into electrical signals by scanning with electron beams. In order to convert the rates of transmission into optical densities, the electrical signals are led to the respective logarithmic converting circuits 1 6R, 1 6G and 16B. The calibration signals generated by the calibration signal generator 26 are then added to the electrical signals after the logarithmic conversion, by using the respective adders 48, 49 and 50, and the thus-obtained electrical signals are fed to the parallel-series converter 5 1. In the parallel-series converter 5 1, the three parallel electrical signals which are gated at every field are converted into series triple signals such as R, G, B, R, G, B, and they are displayed on the wave-form monitor 25. Thus, the densities of the separated colours of the original picture 12 can be simultaneously measured. Though three-colour separation is exemplified in this embodiment, it will be easily understood by those skilled in the art that the present invention is not restricted to the three-colour separation but similarly applicable to four-colour separation.

Further, in place of the three-colour separation system 44 and three TV cameras 45 to 47 shown in Figure 6, a set of R, G and B field sequential filters, one TV camera 23 and a video recording apparatus can be used, in which the image of an original colour picture is converted into R, G and B electrical video signals and they are recorded in the video recording apparatus, and then the recorded electrical signals are simultaneously taken out.

Furthermore, the density measuring device shown in Figure 6 can be applied to a colour proof or proof viewing apparatus such as the apparatus disclosed in Japanese Laid-open Publication No. 40819 of 1974, "Method for displaying colour images" (Dainippon Screen Mfg. Co. Ltd.). As schematically shown in Figure 7, the image of original picture 12 is taken by a colour TV camera 62 of the colour proof apparatus 61 to obtain three-colour video signals of R, G and B, and the obtained signals are displayed on a colour monitor 64 having a colour picture tube, after passing the video signals through a tone correcting circuit 63. By observing the image on the colour monitor 64, the tone correcting circuit 63 is manipulated until the image on the colour monitor 64 becomes satisfactory. Thus, the conditions for colour separation in platemaking can be obtained from the values of correction in the tone correcting circuit 63.

When the input signals for the logarithmic converting circuit 16 of Figure 6 are taken from the TV camera 62 of the colour proof apparatus 61, the optical densities of the original colour picture 12 can be measured and the conditions for the colour separation process can be obtained more accurately and easily.

Another exemplary application of the density measuring device of the present invention will be described in the following with reference to Figure 7. In this embodiment, the portion to be measured on the original colour picture 12 is indicated on the colour monitor 64 of the colour proof apparatus 61, and the optical density of such portion is indicated on the wave-form monitor 25.

The electrical signal obtained by the TV camera 62, for example R (red) signal, is displayed on the wave-form monitor 25 through the above-described logarithmic converting circuit 16R, the adder 48, the parallel-series converter 51 and the gate circuit 71. While a slit signal generator 73 is supplied with horizontal drive signals (HD), vertical drive signals (VD) and spot position shifting signals obtained from a phase controlling circuit 72, the positioning signals of a square spot (respectively two vertical and horizontal lines) are produced by the slit signal generator 73 triggered with the HD and VD signals. These positioning signals are supplied to the colour monitor 64 and are mixed to video signals.

Thus, as shown in Figure 8A, a square spot 81 and the image of the original picture 12 are simultaneously displayed on the colour monitor 64.

The positioning signals generated by the slit signal generator 73 are supplied to the abovementioned gate circuit 71 by way of gate generator 74 so as to cut out the electric signals other than the square spot and retrace blanking interval by the gate circuit 71, and thereby displaying only the electric signals 37 within the square spot and calibration signals 38 on the wave-form monitor 25. Of course, the position of the square spot 81 can be freely moved by the phase controlling circuit 72 and, by observing the image on the colour monitor 64, the position of the square spot 81 can be shifted so as to measure the optical density of desired portions on the original colour picture 12.

Since the functions of the logarithmic converting circuit 16, the adder 48, the parallelseries converter 51 and the calibration signal generator 26 are the same as those of the foregoing embodiments, a detailed explanation thereof are omitted here.

As described above in respect of the illustrated embodiment, the optical densities of the whole portions of an original colour picture as well as of monochromatic picture can be indicated, and the range of optical densities, the maximum density, the minimum density and the density of a certain portion can be easily measured; in addition, the comparison of densities in several points can also be achieved.

Therefore, these embodiments of measuring devices in accordance with the present invention are quite useful for the density measurement in colour plate-making.

WHAT WE CLAIM IS: 1. A measuring device for measuring an optical characteristic of an object, which measuring device comprises scanning means for scanning an object to produce an optical characteristic signal relating to an optical characteristic of the scanned object, display means responsive to the optical characteristic signal for displaying the optical characteristic signal in graphic form and marker signal generating means responsive to the scanning means and independent of the optical characteristic signal for generating a signal to produce on the display means a plurality of calibration markers indicative of values of the optical characteristic to be measured and in a predetermined relationship to the optical characteristic signal so that the measurement of the displayed optical characteristic signal can be read directly from the display means by visually determining the relative position of the, or part of the, optical characteristic signal in relation to the calibration markers.

2. A measuring device according to Claim 1, wherein the optical characteristic signal produced, in use, by the scanning means includes a retrace blanking interval, wherein the marker signal generating means generates, in use, the signal for producing calibration markers during the retrace blanking interval and includes means for adding the signal for producing calibration markers to the optical characteristic signal to produce a combined signal and wherein the display means is responsive to the combined signal to display the combined signal in graphic form on the display means.

3. A measuring device for measuring an optical characteristic of a subsection of an object, which measuring device comprises scanning means for scanning an object to produce an optical characteristic signal relating to an optical characteristic of the scanned object, identification signal deriving means responsive to the scanning means for deriving an identification signal to identify a subsection to be measured of the object, display means responsive to the optical characteristic signal for displaying at least a portion of the optical characteristic signal in graphic form, marker signal generating means responsive to the scanning means and independent of the optical

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. video signals through a tone correcting circuit 63. By observing the image on the colour monitor 64, the tone correcting circuit 63 is manipulated until the image on the colour monitor 64 becomes satisfactory. Thus, the conditions for colour separation in platemaking can be obtained from the values of correction in the tone correcting circuit 63. When the input signals for the logarithmic converting circuit 16 of Figure 6 are taken from the TV camera 62 of the colour proof apparatus 61, the optical densities of the original colour picture 12 can be measured and the conditions for the colour separation process can be obtained more accurately and easily. Another exemplary application of the density measuring device of the present invention will be described in the following with reference to Figure 7. In this embodiment, the portion to be measured on the original colour picture 12 is indicated on the colour monitor 64 of the colour proof apparatus 61, and the optical density of such portion is indicated on the wave-form monitor 25. The electrical signal obtained by the TV camera 62, for example R (red) signal, is displayed on the wave-form monitor 25 through the above-described logarithmic converting circuit 16R, the adder 48, the parallel-series converter 51 and the gate circuit 71. While a slit signal generator 73 is supplied with horizontal drive signals (HD), vertical drive signals (VD) and spot position shifting signals obtained from a phase controlling circuit 72, the positioning signals of a square spot (respectively two vertical and horizontal lines) are produced by the slit signal generator 73 triggered with the HD and VD signals. These positioning signals are supplied to the colour monitor 64 and are mixed to video signals. Thus, as shown in Figure 8A, a square spot 81 and the image of the original picture 12 are simultaneously displayed on the colour monitor 64. The positioning signals generated by the slit signal generator 73 are supplied to the abovementioned gate circuit 71 by way of gate generator 74 so as to cut out the electric signals other than the square spot and retrace blanking interval by the gate circuit 71, and thereby displaying only the electric signals 37 within the square spot and calibration signals 38 on the wave-form monitor 25. Of course, the position of the square spot 81 can be freely moved by the phase controlling circuit 72 and, by observing the image on the colour monitor 64, the position of the square spot 81 can be shifted so as to measure the optical density of desired portions on the original colour picture 12. Since the functions of the logarithmic converting circuit 16, the adder 48, the parallelseries converter 51 and the calibration signal generator 26 are the same as those of the foregoing embodiments, a detailed explanation thereof are omitted here. As described above in respect of the illustrated embodiment, the optical densities of the whole portions of an original colour picture as well as of monochromatic picture can be indicated, and the range of optical densities, the maximum density, the minimum density and the density of a certain portion can be easily measured; in addition, the comparison of densities in several points can also be achieved. Therefore, these embodiments of measuring devices in accordance with the present invention are quite useful for the density measurement in colour plate-making. WHAT WE CLAIM IS:

1. A measuring device for measuring an optical characteristic of an object, which measuring device comprises scanning means for scanning an object to produce an optical characteristic signal relating to an optical characteristic of the scanned object, display means responsive to the optical characteristic signal for displaying the optical characteristic signal in graphic form and marker signal generating means responsive to the scanning means and independent of the optical characteristic signal for generating a signal to produce on the display means a plurality of calibration markers indicative of values of the optical characteristic to be measured and in a predetermined relationship to the optical characteristic signal so that the measurement of the displayed optical characteristic signal can be read directly from the display means by visually determining the relative position of the, or part of the, optical characteristic signal in relation to the calibration markers.

characteristic signal for generating a signal to produce on the display means a plurality of calibration markers indicative of values of the optical characteristic to be measured and in a predetermined relationship to be optical characteristic signal and gate means responsive to the optical characteristic signal and rendered effective by the identification signal for enabling the display means to display only that portion of the optical characteristic signal corresponding to the optical characteristic of the subsection of the object identified by the identification signal so that the measurement of the optical characteristic of the identified subsection can be read directly from the display means by visually determining the relative position of the, or part of the, optical characteristic signal in relation to the calibration markers.

4. A measuring device according to Claim 3, wherein the optical characteristic signal produced, in use, by the scanning means includes a retrace blanking interval, wherein the marker signal generating means generates, in use, the signal for producing calibration markers during the retrace blanking interval and includes means for adding the signal for producing calibration markers to the optical characteristic signal to produce a combined signal and wherein the gate means is responsive to the combined signal so that the calibration markers and the portion of the optical characteristic signal enabled to be displayed by the gate means are displayed, in use, on the display means.

5. A measuring device according to Claim 3 or 4, which further comprises object display means for displaying an image of the object scanned by the scanning means and wherein the object display means is responsive to the identification signal for identifying the subsection to be measured of the object on the object display means.

6. A measuring device according to Claim 3, 4 or 5, wherein the identification deriving means comprises a signal generator for generating first and second positioning signals, the first positioning signal identifying, in use, the horizontal position of the subsection to be measured and the second positioning signal identifying, in use, the vertical position of the subsection to be measured.

7. A measuring device according to Claim 6, wherein the object display means is responsive to the first and second positioning signals for displaying a marker on the image displayed on the object display means corresponding to the subsection to be measured.

8. A measuring device according to Claim 1 or 2, wherein the scanning means comprises a flying spot scanner and a photo-electric transducer.

9. A measuring device according to any one of Claims 1 to 7, wherein the scanning means comprises a television camera.

10. A measuring device according to any one of the preceding claims, for measuring an optical characteristic of an object having a plurality of colours, wherein the scanning means includes multi colour separation means for separating the optical characteristic signal into a plurality of colour signals, each of the colour signals corresponding to the optical characteristic of one of the colours of the scanned object and wherein the display means is responsive to each of the colour signals for displaying separately on the display means the colour signals in graphic form.

11. A measuring device according to any one of the preceding claims, wherein the marker signal generating means comprises means for generating a signal to produce first and second pluralities of calibration markers on the display means, the first plurality of calibration markers having a scale which is more finely divided than the scale of the second plurality of calibration markers.

12. A method of measuring an optical characteristic of an object, which method comprises scanning an object to produce an optical characteristic signal relating to an optical characteristic of the scanned object, generating a signal for producing a plurality of calibration markers indicative of values of the optical characteristic to be measured and displaying in graphic form on display means the optical characteristic signal and the plurality of calibration markers, the plurality of calibration markers being displayed in a predetermined relationship with respect to the optical characteristic signal so that the measurement of the displayed optical characteristic signal can be read directly from the display means by visually determining the relative position of the, or part of the, optical characteristic signal in relation to the calibration markers.

13. A measuring device for measuring an optical characteristic of an object, substantially as hereinbefore described with reference to, and as shown in, Figures 2, 3A and 3B of the accompanying drawings.

14. A measuring device for measuring an optical characteristic of an object, substantially as hereinbefore described with reference to, and as shown in, Figures 9, 3A and 3B modified by Figure 4 of the accompanying drawings.

15. A measuring device for measuring an optical characteristic of an object, substantially as hereinbefore described with reference to, and as shown in, Figure 5 of the accompanying drawings.

16. A measuring device for measuring an optical characteristic of an object, substantially as hereinbefore described with reference to, and as shown in, Figure 6 of the accompanying drawings.

17. A measuring device for measuring an optical characteristic of an object, substantially as hereinbefore described with reference to, and as shown in, Figures 7, 8A and 8B of the accompanying drawings.

18. A method of measuring an optical characteristic of an object, substantially as hereinbefore described with reference to Figures 2 and 3A of the accompanying drawings.

19. A method of measuring an optical characteristic of an object, substantially as hereinbefore described with reference to Figures 2 and 3A modified by Figure 3B of the accompanying drawings.

20. A method of measuring an optical characteristic of an object, substantially as hereinbefore described with reference to Figures 2 and 3A modified by Figure 4 of the accompanying drawings.

21. A method of measuring an optical cliaracteristic of an object, substantially as hereinbefore described with reference to Figure 5 of the accompanying drawings.

22. A method of measuring an optical characteristic of an object, substantially as hereinbefore described with reference to Figure 6 of the accompanying drawings.

23. A method of measuring an optical characteristic of an object, substantially as hereinbefore described with reference to Figures 7, 8A and 8B of the accompanying drawings.