Life expiration detector for light source of image processing apparatus

An image forming apparatus includes a detector for detecting light intensities of light from a light source, and a discrimination unit for obtaining the relative ratio of chroma signals of light with two or more wavelengths at the light intensities of the light source detected by the detector, to thereby discriminate life expiration of the light source. Data of the relative ratio of chroma signals of light with two or more wavelengths at a time of life expiration of the light source is obtained in advance. Thereafter, the light intensity of the light source is detected to obtain the actual relative ratio of the chroma signals of light with two or more wavelengths. Based on these data, the life expiration of the light source is discriminated.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an image forming apparatus such as a 
thermal copying machine equipped with a scanner to irradiate light from an 
illumination lamp onto an original and read out image data from the 
reflected light. 
2. Description of the Related Art 
In a thermal color copying machine which uses a thermal ink ribbon with 
plural types of colors to make a color copy, for example, light is 
irradiated onto an original from an illumination lamp (light source), 
image data of the original is optically read out from the reflected light, 
and this image data is converted into color data corresponding to the 
individual inks of the thermal ink ribbon. In accordance with the color 
data, ink of the associated ink portion of the thermal ink ribbon is 
melted by a thermal head (heat-sensitive head) and transferred onto a 
sheet of paper (image-forming medium). in this manner, different colors 
are sequentially transferred onto the paper to make a color copy. 
In some of the above type thermal color copying machines, the life 
expiration of the lamp is checked on the basis of the intensity of light 
from the lamp. In other words, the lamp's life expiration is checked on 
the basis of reduction in intensity of light. If the required intensity of 
light cannot be provided from a lamp in use any more, this lamp needs 
replacement. 
Even if there is a sufficient intensity of light to scan a monochromatic 
original (two-colored (black and white) original), however, the ratio of 
chroma signals of light (relative ratio of red (R), green (G) and blue 
(B)) may actually vary due to reduction in color temperature of light 
which is caused by deterioration of the lamp. In this case, the color 
copying machine of the aforementioned type which checks the life 
expiration of the lamp based only on the intensity of light, cannot 
discriminate color imbalance caused by deterioration of the lamp. When a 
user uses a lamp whose life expiration has already been reached, without 
being aware of a change in ratio of R, G and B, therefore, the color tone 
of a color original cannot be reproduced with a high fidelity. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of this invention to provide an image forming 
apparatus which can accurately check a change in color balance due to 
deterioration of a light source to thereby enhance color reproducibility. 
The image forming apparatus of the present invention comprises means for 
detecting the intensity of light from a light source and means for 
discriminating the life expiration of the light source by obtaining a 
relative ratio of chroma signals of light with two or more types of 
wavelengths in the intensity of light of the light source detected by the 
detecting means. 
According to the present invention, data about the relative ratio of chroma 
signals of light with two or more types of wavelengths at the expected end 
of the life expiration of the light source is obtained in advance. 
Thereafter, the intensity of light from the light source is detected to 
acquire the actual relative ratio of chroma signals of light with two or 
mote types of wavelengths for discrimination of the life expiration of the 
light source.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A preferred embodiment of this invention will no be described referring to 
the accompanying drawings. 
FIGS. 5 and 6 illustrates a thermal color copying machine as one example of 
an image forming apparatus. An image data scanner 2 is detachably mounted 
on the top portion of a main body 1. This scanner 2 is provided with an 
openable original cover 3. Below the cover 3 lies an original stand 4 made 
of transparent glass. The scanner 2 causes its exposure optical system to 
reciprocate along the bottom surface of the original stand 4 to optically 
scan an original placed on the original stand and photoelectrically 
converts the attained optical data into an electric signal. The data 
converted by the scanner 2 is supplied to an image forming unit 5 
detachably mounted on the right side of the main body 1. The image forming 
unit 5 forms an image on a sheet of paper as an image-forming medium in 
accordance with the converted data. 
A manipulation panel 6 is provided on the top front of the image forming 
unit 5. A guide section 11 used for manual paper feeding is openably 
provided on the front of the image forming unit 5, and a paper receiving 
tray 12 for receiving a sheet of paper having an image transferred thereon 
is provided on the top of the unit 5. Further, a paper feeding cassette 13 
capable of holding plural sheets of paper P is loadably provided in the 
main body 1 lying under the image forming unit 5. Reference numeral 8 
denotes a door through which a thermal ink ribbon (to be described later) 
as a transfer agent is set or detached. 
As shown in FIGS. 6 to 8, for example, the image data scanner 2 comprises a 
first carriage 22 having an illumination lamp 23 as a light source, etc. 
mounted thereon, a second carriage 24 for deflecting an optical path by 
means of a mirror, a zoom lens 21, a mirror section 26 for guiding the 
reflected light from an original O to a photoelectric converter 25 and 
compensating the length of the optical path when magnification is changed, 
the photoelectric converter 25 for receiving the reflected light from the 
original O, and a driving system (not shown) for altering the positions of 
these individual elements. 
As shown in FIG. 7, the first carriage 22 is mounted with the illumination 
lamp 2 for irradiating light onto the original O, a reflector 27 for 
converging light from the lamp 23 onto the surface of the original O, a 
mirror 28 for guiding the reflected light from the original O toward the 
second carriage 24, a filter section 29 and a photosensor (detecting 
means) 30. The filter section 29 has a red (R) filter, a green (G) filter 
and a blue (B) filter, and also has a mechanism (see FIG. 7A) for 
selectively inserting the R, G and B filters onto the light-receiving 
portion of the photosensor 30. In checking the life expiration of the 
illumination lamp 23, for example, this mechanism sets the R, G and B 
filters one by one on the photosensor 30 to separate the reflected light 
from a white original (reference original) into light components with 
different wavelengths associated with R, G and B and supplies the light 
components with the three types of wavelengths to the photosensor 30. The 
R, G and B primary-color filters in the filter section 29 may be replaced 
with C (cyan), G (green) and Y (yellow) color filters. 
The second carriage 24 is mounted with mirrors 24a and 24b for guiding the 
light led by the mirror 28 to the zoom lens 21. As shown in FIG. 8, the 
first and second carriages 22 and 24 are connected together by a timing 
belt 31 so that the second carriage 24 moves in the same direction at half 
the speed of the first carriage 22. This permits scanning in such a way 
that the optical path to the zoom lens 21 is constant. 
The zoom lens 21 has a fixed focus distance and is therefore moved along 
the optical axis when magnification is change. 
As shown in FIG. 7, the mirror section 26 comprises two mirrors 26a and 26b 
whose positions change in accordance with a change in length of the 
optical path associated with the selected magnification. Light from the 
zoom lens 21 is deflected by the two mirrors 26a and 26b to guide it the 
photoelectric converter 25. 
The photoelectric converter 25 performs photoelectric conversion of the 
reflected light from the original O to separate image data of the original 
O into C, G and Y (or R, G and B) chroma signals and output them. This 
converter 25 is mainly constituted by a CCD type line image sensor. In 
this case, one pixel of the original O corresponds to three consecutive 
elements (C, G and Y) of the CCD sensor. The output of the photoelectric 
converter 25 is supplied to an A/D converter 91 which will be described 
later. 
The first carriage 22, second carriage 24, zoom lens 21 and mirror section 
26 are each moved by a stepping motor (not shown). 
As shown in FIG. 8, the first and second carriages 22 and 24 are moved in 
accordance with the movement of the timing belt 35 stretching between a 
drive pulley 32 coupled to the rotational shaft of the stepping motor and 
idle pulleys 33 and 34. 
The mirror section 26 and zoom lens 21 are moved by separate stepping 
motors (not shown). The zoom lens 1 has its spiral shaft (not shown) 
rotated by the associated stepping motor and moves along the optical shaft 
by the movement of this shaft. 
Both of the mirror section 26 and photoelectric converter 25 may arranged 
in one bracket so that the mirrors 26a, 26b and the photoelectric 
converter 25 are moved integrally. 
The image forming unit 5 has a platen 50 disposed at approximately the 
center portion and a thermal head 51 serving as a recording head 
(heat-sensitive head disposed in front of the platen 50 (on the left in 
FIG. 6) so that the head 51 can come into contact with or move away from 
the platen (see FIG. 6). 
Further, the thermal head 51 is accommodated in the space within a ribbon 
cassette Rc with a thermal ink ribbon (thermal ribbon) 52 coming between 
the head 51 and the platen 50. With the ink 52 in this position, when 
paper (image-forming medium) is pressed against the platen 50 and heating 
elements (not shown) of the thermal head 51 formed in line dots is heated 
in accordance with color data, ink on the ink ribbon 52 is heated and 
melted onto the paper. 
A paper feeding roller 53 is provided obliquely below the platen 50 in the 
main body 1 to feed out sheets of paper P from the paper feeding cassette 
13 one by one. The fed-out paper P is guided, passing through a paper 
guiding path 54, to a resist roller 55 located obliquely above the paper 
feeding roller 53, and has its fore edge aligned by this roller 55. The 
paper P is then fed to the platen 50 and wound around it by pressing 
rollers 56 and 57. In this manner, the paper P can be accurately fed to 
the platen 50. 
A manual feeding detecting switch 69 constituted by, for example, a 
photocoupler, which detects paper manually fed, is provided in the guide 
section 11. A pair of rollers 66, which is operated in accordance with the 
detection by this switch 69 to supply the manually-fed paper, are also 
provided in the guide section 11. The paper supplied by the roller pair 66 
is guided to the resist roller 55 through a guide path 68 and a switch 67 
constituted by a microswitch, for example, and is accurately supplied to 
the platen 50 to be wound therearound, as described above. 
The switch 67 is normally ON and is turned OFF when paper passes 
therethrough. The guide section 11 is provided with manual-feeding guides 
(not shown) which are set in accordance with the width of paper when the 
paper is supplied. Data of the mutual distance between the manual-feeding 
guides is supplied to a main controller (to be described later). 
The thermal head 51 presses the paper P against the platen 50 through the 
thermal ink ribbon 52, and transfers ink 60.sub.1 onto the paper P by 
melting ink 60 on the ink ribbon 52 with heat, as shown in FIG. 9. 
The thermal ink ribbon 52 has Y, M and C ink sections 60a, 60b and 60c 
arranged in substantially the same size as the paper P as indicated by the 
range "a" in FIG. 10 or Y, M, C and BL (black) ink sections 60a, 60b, 60c 
and 60d as indicated by the range "b." The paper P is returned to the 
ink-transfer start position for each color so that the colors are 
accurately and sequentially placed one on another. 
Those side edge portions of the thermal ink ribbon 52 which correspond to 
the respective ink portions 60a-60d are provided with bar codes BC 
necessary for discriminating the ink portions 60a-60d and align the fore 
end of each of the ink portions 60a-60d with the fore end of the paper P. 
The bar codes BC are read out by a bar code detector (not shown). 
When the black ink portion 60d is provided on the thermal ink ribbon 52, 
this ink portion is used to make black clearer. Even without the black ink 
portion 60d, black can substantially be made by putting the three colors 
(60a-60c) one on another. 
The paper P is reciprocated by the number of colors by the rotation of the 
platen 50, and the path of the paper P is led onto first and second guides 
61 and 62 sequentially provided along the bottom surface of the paper 
receiving tray 12. 
Ink transfer will now be described referring to FIGS. 11A-11D. First, paper 
P fed out from the paper feeding cassette 13 passes through a section 
where the resist roller 55 and a first separate gate 63 are located and is 
wound around the platen 50 (see FIG. 11A). 
Then, the platen 50 is rotated by a pulse motor as a drive source (not 
shown) to feed the paper P at a given speed, and the heating elements (not 
shown) of the thermal head 51 formed in line dots along the shaft of the 
platen 50 are heated in accordance with color data, whereby the ink 60 on 
the ink ribbon 52 is transferred onto the paper P. 
The fore end of the paper P passing the platen 50 is sent over the first 
guide 61 provided along the bottom surface of the paper receiving tray 12 
by a second separate gate 64 (see FIG. 11B). 
The paper P having one color ink 60 transferred thereon in this manner is 
sent back by the reverse rotation of the platen 50 and is sent over the 
second guide 62 provided along the bottom surface of the first guide 61 by 
a change in rotation of the first separate gate 63 (see FIG. 11C). 
A plurality of colors can be transferred onto the paper P by reciprocally 
moving the paper P in the above manner. 
Finally, the paper P having all the required colors transferred thereon is 
guided to a pair of paper discharging rollers 65 by the second separate 
gate 64, and is discharged onto the paper receiving tray 12 (see FIG. 
11D). 
With paper manually fed, although not illustrated, the paper is supplied to 
the position of the resist roller 55 by the roller pair 66 and is then 
subjected to ink transfer as described above. 
FIG. 12 illustrates the aforementioned manipulation panel 6. This panel 6 
is provided with a print key 41 for instructing the start of printing 
(image formation), ten keys 42 for specifying the number of prints, a 
clear/stop key 43 for instructing to clear the print number specified and 
instructing to stop printing, a number indicator 44 for displaying the 
number of prints, etc., a magnification setting section 45 for setting a 
magnification (magnifying ratio) of an image to be formed, a display 48 
for displaying various data, an original mode key 49.sub.1 for selecting a 
mode in accordance with the quality of the original, a display 49.sub.2 
for displaying the selected mode, a density specifying key 47.sub.1 for 
selectively setting the printing density in five levels, a display 
47.sub.2 for displaying the set density, and a check mode specifying key 
46 operable in checking the life expiration of the illumination lamp 23. 
The display 48 comprises a jam indicator 48.sub.1 which is lit when paper 
jamming occurs in the main body 1, a ribbon indicator 48.sub.2 for 
indicating various statuses such as no more available ribbon in the ribbon 
cassette Rc mounted in the main body 1 and not cassette mounted, a paper 
indicator 48.sub.3 for indicating the loading status of the paper feeding 
cassette 13 or presence/absence of paper, a print disable indicator 
48.sub.4 and a print enable indicator 48.sub.5 for indicating the status 
of the main body 1, a size indicator 48.sub.6 for indicating the size of 
paper in the loaded paper feeding cassette 13, and a lamp life expiration 
indicator 48.sub.7 for indicating the life expiration of the illumination 
lamp in check mode. 
FIG. 1 schematically illustrates the general control system which comprises 
a main controller 81, a first sub-controller 82 and a second 
sub-controller 82. The main controller 81 is coupled to the manipulation 
panel 6, a correction circuit 84, a luminance/color-difference separator 
85, a picture quality enhancer, a chroma signal converter 87, a digitizer 
88, the first sub-controller 82 and the second sub-controller 83, and 
controls the operation of all the mentioned units. 
The first sub-controller 82 is coupled to a light source controller 89, a 
motor driver 90, the photoelectric converter 25, the A/D converter 91 and 
a resolution converter 92, and controls the operation of these units. The 
light source controller 89 comprises, for example, a lamp driver 71 for 
controlling the activation of the illumination lamp 23 and the intensity 
light therefrom, a light intensity detector 72 for detecting the intensity 
of light from the lamp 23 from the output of the photosensor 30, and an 
A/D converter 73 for subjecting the output of the detector 72 to A/D 
conversion. The motor driver 90 drives a scanning motor (stepping motor) 
80 which moves the first and second carriage 22 and 24, for example. 
The second sub-controller 83 is coupled to a thermal head temperature 
controller 93, the thermal head 51, various detection switches 94 and a 
driver 95, and controls the operation of these units. The driver 95 is 
coupled to a driving mechanism 96 such as a motor and solenoid for driving 
the zoom lens 21, mirror section 26, platen 50, etc. 
The correction circuit 84 executes normalization (shading correction or 
correction of variation in the photoelectric converter 25) based on the 
image data (after resolution conversion) attained by A/D conversion of the 
reflected light from the original and the reference data. 
FIG. 2 is presented for a further description of the chroma signal 
converter 87. This chroma signal converter 87 outputs to the digitizer 88 
a signal x which is attained by selecting one of Y, M, C and B.sub.L 
chroma signals from a luminance signal (I), a color-difference signal 1 
(Cl) and a color difference signal 2 (C2) from the picture quality 
enhancer 86. The selection of Y, M, C, or B.sub.L chroma signal is done by 
the main controller 81. More specifically, the main controller 81 selects 
one of the Y, M, C and B.sub.L chroma signals sent to the digitizer by a 
combination of signals a and b, as indicated in the following Table 1. The 
chroma signals are automatically selected one by one by a command from the 
main controller 81 (e.g., in the sequence of 
Y.fwdarw.M.fwdarw.C.fwdarw.B.sub.L). 
TABLE 1 
______________________________________ 
a b x 
______________________________________ 
0 0 Y 
0 1 M 
1 0 C 
1 1 B.sub.L 
______________________________________ 
The digitizer 88 has a memory 88A (FIG. 2A) for storing four (Y, M, C and 
B.sub.L) chroma signals from the chroma signal converter 87 as data of 
positions on the original for each color. In accordance with a command 
from the main controller 81, a pseudo gradation is given, by a dither 88B, 
to the chroma signal of each position stored in the memory 88A and the 
resultant signal is digitized by a digitizer 88C. Four digital chroma 
signals each having a pseudo gradation are then selectively output. 
A description will now be given of the normal copying operation with the 
above arrangement. Assume now that a user has specified the copying 
conditions such as a copying magnification using the manipulation panel 6 
(FIG. 12), placed an original on the original stand 4, then pressed the 
print key 41 on the panel 6. Then, the main controller 81 (FIG. 1) 
controls the driving mechanism 96 through the second sub-controller 83 and 
driver 95 to move the zoom lens 21, etc. in accordance with the specified 
magnification. The main controller 81 also controls the first 
sub-controller 8 and the lamp driver 71 of the light source controller 89 
to turn on the illumination lamp 23 and drives the scanning motor 80 
through the first sub-controller 82 and motor driver 90 to move the first 
and second carriages 22 and 24. As a result, light from the illumination 
lamp 23 (see FIG. 6) is irradiated onto the original through the original 
stand 4. 
The reflected light from the original is led to the photoelectric converter 
25 sequentially through the mirrors 28, 24a and 24b, zoom lens 21 and 
mirrors 26a and 26b (see FIG. 7). The photoelectric converter 25 (such as 
a CCD linear image sensor with color filters) separates the reflected 
light into analog C, G and Y chroma signals, which are then sent to the 
A/D converter 91. 
The A/D converter 91 converts each analog chroma signal into a digital 
signal. The signals from the A/D converter 91 associated with the original 
are sent out the resolution converter 92. 
The resolution converter 92 (FIG. 1) performs resolution conversion to make 
the resolution of the photoelectric converter 25 (e.g., 400 dots per inch) 
coincide with that of the thermal head 51 (e.g., 200 dots per inch), and 
the conversion result is sent to the correction circuit 84. 
The correction circuit 84 normalizes the individual C, G and Y chroma 
signals from the resolution converter 92 using reference data and executes 
a process for correcting a variation in the photoelectric converter 25 
(shading correction). The result of the correction is sent to the 
luminance/color-difference separator 85. 
The separator 85 subjects the C, G and Y chroma signals from the correction 
circuit 84 to various arithmetic operations to separate them into a 
luminance signal (I), a color difference signal 1 (C1) and a color 
difference signal 2 (C2), where are in turn sent to the picture quality 
enhancer 86. 
The picture quality enhancer 86 analyzes the received signals and performs 
a picture quality enhancing process such as edge emphasis. The resultant 
signals are sent to the chroma signal converter 87. 
The converter 87 performs color conversion based on the luminance signal 
and color difference signals 1 and 2 undergone the picture quality 
enhancement to convert them into one (a signal corresponding to densities) 
of Y, M, C and B.sub.L chroma signals (primary colors (Y, M and C) at the 
time of printing pulse black (B.sub.L)). This signal is sent to the 
digitizer 88. 
The digitizer 88 (FIG. 2A) executes surface gradation conversion (88B) 
using a dither method and digitalization on the chroma signal (one of Y, 
M, C and B.sub.L) from the chroma signal converter 87. The digital signal 
is sent to the thermal head temperature controller 93. 
Based on the digital signal from the digitizer 88 and position data from 
the second sub-controller 83 (FIG. 1), this controller 93 a print signal 
(color data) to the thermal head 51. 
Meantime, the driving mechanism 96 is controlled through the second sub 
controller 83 and driver 95 by a command given from the main controller 81 
in response to the pressing of the print key 41 on the manipulation panel 
6 (FIG. 12), so that the paper feeding roller 53, resist roller 55 and 
platen 50 are driven. As shown in FIG. 11A, a sheet of paper P in the 
paper feeding cassette 13 is fed out by the roller 53 and this paper P is 
fed through the paper guide path 54 by the roller 55. The paper P is 
guided via the pressing roller 56 to the platen 50 and is wound 
therearound. 
Under the above situation, when the paper P is supplied to the printing 
position of the thermal head 51 by the rotation of the platen 50, the head 
51 melts color ink 60 (e.g., 60.sub.1) of the thermal ink ribbon 52, which 
is associated with a print signal, to execute printing (image forming) on 
the paper P wound around the platen 50, as shown in FIG. 9. 
When multi-color printing by superimposing one color on another or 
monochromatic printing is completed, the main controller 81 controls the 
first sub-controller 82 and the lamp driver 71 of the light source 
controller 89 to turn off the illumination lamp 23. The driving mechanism 
96 is controlled through the second sub-controller 83 and driver 95 so 
that the paper P around the platen 50 is discharged on the tray 12, as 
shown in FIG. 11B, for example, thus completing the copying operation. 
If paper is manually fed from the guide section 11 (FIG. 6), the copying 
operation is executed in the same manner as described above. 
A description will now be given of the case where the check mode specifying 
key 46 on the manipulation panel 6 (FIG. 12) is operated. 
Upon pressing the key 46, the red, green and blue filters of the filter 
section 29 in FIG. 7A are inserted over the light receiving portion of the 
photosensor 30 one by one by driving means (not shown). 
When a white original, for example, is placed on the original stand 4 (FIG. 
6) and the print key 41 on the manipulation panel 6 is pressed, the main 
controller 81 (FIG. 1) controls the light source controller 89 and motor 
driver 90 through the first sub-controller 82. As a result, the 
illumination lamp 23 is turned ON by the lamp driver 71 of the controller 
89 and the scanning motor 80 is driven by the motor driver 90. 
Consequently, light from the illumination lamp 23 is irradiated onto the 
white original through the original stand 4, and the reflected light from 
this original enters the photosensor 30 through the filter section 29. In 
this case, the photosensor 30 receives light passing each filter by 
inserting the individual filters of the filter section 29 onto the light 
receiving portion of the photosensor 30 with the scanning of the white 
original. 
Upon completion of scanning the white original, the main controller 81 
causes the first sub-controller 82 to control the lamp driver 71 of the 
light source controller 81 to thereby turn the illumination lamp OFF. 
Further, the motor driver 90 is controlled to drive the scanning motor 80 
to thereby set the first carriage 22 at a predetermined position. 
The output of the photosensor 30 (FIG. 1) is supplied to the light 
intensity detector 72 of the light source controller 89. The detector 72 
detects the light intensity of each of R, G and B components from the 
outputs of the photosensor 30 attained by executing color separation by 
the filter section 29 (FIG. 7A). The detection result of the detector 72 
is sent to the A/D converter 73 where it is subjected to A/D conversion. 
The resultant signal is supplied through the first sub-controller 82 to 
the main controller 81. 
Based on data of the light intensities of the R, G and B components 
supplied from the A/D converter 73, the main controller 81 acquires a 
ratio of these components and checks whether or not the life of the 
illumination lamp 23 has expired (whether or not the lamp should be 
replaced with a new one) from, for example, a change in ratio of the R, G 
and B components (change in balance). If it is discriminated that the life 
expiration of the lamp 23 has reached, the main controller 81 turns on the 
lamp life expiration indicator 48.sub.7 of the display 48 on the 
manipulation panel 6 to inform a user of the event. 
The relation between the life expiration of the lamp 23 and chroma signals 
(R, G, B) of light will be described below. 
Assume that the illumination lamp 23 (FIG. 7) is constituted by a 
fluorescent lamp which irradiates white light using a plurality of 
fluorescent members. Even if one of the fluorescent members is 
deteriorated, the balance between the R, G and B components of the white 
light would be changed. With such a lamp 23 in use, a reproduced (printed) 
image of a color original or the like is influenced by such a change in 
white balance, thus deteriorating the color reproducibility. 
FIG. 3A illustrates that the R, G, B components of white light are in ideal 
state. In this case, provided that the distribution of the intensities of 
the R, G and B color components are given by functions R(x), G(x) and 
B(x), respectively, the individual components can be expressed as follows: 
##EQU1## 
where x is a wavelength, +a denotes the range of integration for red, +b 
denotes the range of integration for green, and +c denotes the range of 
integration for blue. 
If the lamp 23 is deteriorated to cause a change in R, G and B components 
as shown in FIG. 3B, the functions R(x), G(x) and B(x) are varied. 
Accordingly, the R, B and B color components do not represent an accurate 
white balance. Further, resolution in A/D conversion for the color 
components whose intensities are decreased due to deterioration of the 
lamp is also reduced, thus resulting in probable color deterioration or 
reproduction of the wrong color. 
If the illumination lamp 23 is constituted by a halogen lamp, the light 
intensity of the R component (FIG. 4A), which is originally very large, 
becomes even greater (i.e., the function R(x) significantly varies (see 
FIG. 4B)). Therefore, the function R(x) cannot be corrected by the shading 
correction alone, thus adversely influencing color reproduction (i.e., 
breading the white balance). 
In view of the above, the main controller 81 discriminates the life 
expiration of the illumination lamp 23 from the ratio (balance; for 
example, .intg.Rdx/.intg.Gdx, .intg.Bdx/.intg.Gdx) of the light 
intensities of the R, G and B components attained when a white original is 
scanned. In other words, using a change in R, G and B components which 
influences color reproduction, the ratio (.intg.Rds/.intg.Gds, etc.) of 
the R, G, B components at the threshold (life expiration of the lamp 23) 
of that change in R, G and B components which does not influence color 
reproduction much, is compared with check level data (e.g., 0.6) as a 
reference point. This discrimination is executed by, for example, a 
processor 132 shown in FIG. 13 and the check level data is stored in 
advance in a memory 133. 
The life expiration of the lamp may be checked by the hardware arrangement 
as shown in FIG. 13. 
A white reference plate REF for determining reference white is placed on 
the original stand 4 in FIG. 7 and light is irradiated onto this white 
reference plate REF from the lamp 23 whose life expiration is to be 
checked. The reflected light from the white reference plate REF is input 
to the photosensor 30 through the RGB filter 29. 
The photosensor 30 sends the three primary color analog signals a30R, a30G 
and a30B subjected to color separation by the RGB filter 29, to an A/D 
converter 130. The A/D converter 130 subjects these analog signals to, for 
example, 8-bit A/D conversion and writes 8-bit digital signals d131R, 
d131G, d131B having 256 gradation levels into RAMs 131R, 131G and 131B, 
respectively. 
-bit digital signals e131R, e131G, e131B read out from the RAMs 131R, 131G 
and 131B are input to an arithmetic processor 132 where the following 
arithmetic operations are executed: 
##EQU2## 
where Rh represents the average of the digital signal e131R (red component 
with respect to the reference white) for specific or non-specific N pixels 
read out from the RAM 131R, Gh represents the average of the digital 
signal e131G (green component with respect to the reference white) for 
specific or non-specific N pixels read out from the RAM 131G, and Bh 
represents the aver age of the digital signal e131B (blue component with 
respect to the reference white) for specific or nonspecific N pixels read 
out from the RAM 131B. The computed average data is stored in the memory 
133. 
Similarly, a black reference plate REF for determining reference black is 
placed on the original stand 4 and light is irradiated onto this black 
reference plate REF from the lamp 23 whose life expiration is to be 
checked. The reflected light from the black reference plate RE is input to 
the photosensor 30 through the RGB filter 29. 
Incidentally, the black reference plate can be omitted if the lamp 23 is 
turned-off when data of the black reference is to be obtained. The output 
of photosensor 30 obtained when the lamp 23 is OFF can be used as the 
black reference data. 
The three primary color signals a30R, a30G and a30B are digitized through 
the A/D converter 130 and written in the RAMs 131R, 131G and 131B, 
respectively. Digital signals e131R, e131G, e131B read out from the RAMs 
131R, 131G and 131B are input to an arithmetic processor 132 where the 
following arithmetic operations are executed: 
##EQU3## 
where Rb represents the average of the digital signal e131R (red component 
with respect to the reference black) for specific or non-specific N pixels 
read out from the RAM 131R, Gb represents the average of the digital 
signal e131G (green component with respect to the reference black) for 
specific or non-specific N pixels read out from the RAM 131G, and Bb 
represents the average of the digital signal e131B (blue component with 
respect to the reference black) for specific or non-specific N pixels read 
out from the RAM 131B. The computed averages are stored in the memory 133. 
Substituting Rh, Gh, Bh, Rb, Gb and Bb obtained from the equations (2) and 
(3) into the following equation (4) yields lamp life expiration check data 
NR, NG and NB. 
##EQU4## 
If any of the data NR, NG and NB obtained by the equation (4) is reduced 
below, for example, 0.6, it is discriminated that the life expiration of 
the lamp 23 has reached. The denominator "256" in the equation (4) 
indicates the number of gradation levels of the data Rh, Rb, Gh, Gb, Bh 
and Bb. 
Upon reception of the result of the discrimination, the main controller 81, 
flickers a predetermined display element (e.g., 48.sub.7 in FIG. 12) on 
the manipulation panel 6 to inform a user that the lamp need replacement. 
FIG. 14 illustrates software that the arithmetic processor (CPU) 132 in 
FIG. 13 executes. 
First, R, G and B digital data d131R, d131G and d131B having 256 gradation 
levels are detected from the reflected light from the black reference 
plate REF (ST10), and the detected R, G and B data are respectively 
written in the RAMs 131R, 131G and 131B. Upon completion of the data 
writing (YES in ST12), the operation enters a data read mode (ST14). 
In data read mode, a target RAM for data readout, e.g., RAM 131R for R 
data, is selected (ST16). When the read RAM is selected, a number N for 
specifying the pixel to be read out is set to 1 (ST18). As a result, the 
value (equal to or greater than 0 but less than 256) corresponding to the 
first pixel (N=1) in the RAM 131R is read out (ST20) and the read-out R 
data value is accumulated in a register (accumulator) in the arithmetic 
processor 132 (ST22). 
Then, the number N is incremented by 1 (ST24). If the resulting value of N 
is equal to or less than 17, the sequence of the processes of ST20-ST24 is 
repeated while incrementing N by 1. 
If N exceeds 17 (YES in ST26), the average of the R data for 17 pixels 
accumulated in the register in the arithmetic processor 132 is computed 
using the equation (3) (ST28), and the computed average R data (Rb) is 
stored in the memory 133 (ST29). 
The same process as done for the R data in ST16-ST29 will be executed for G 
data and B data (NO in ST30). 
When computation of all the averages of the R, G and B data with respect to 
the black reference plate is completed (YES in ST30), R, G and B digital 
data d131R, d131G and d131B having 256 gradation levels are detected from 
the reflected light from the white reference plate REF (ST31), and the 
detected R, G and B data are respectively written in the RAMs 131R, 131G 
and 131B. Upon completion of the data writing (YES in ST32), the operation 
enters a data read mode (ST34). 
In data read mode, a target RAM for data readout, e.g., RAM 131R for R 
data, is selected (ST36). When the read RAM is selected, a number N for 
specifying the pixel to be read out is set to 1 (ST38). As a result, the 
value (equal to or greater than 0 but less than 256) corresponding to the 
first pixel (N=1) in the RAM 131R is read out (ST40) and the read-out R 
data value is accumulated in the register (accumulator) in the arithmetic 
processor 132 (ST42). 
Then, the number N is incremented by 1 (ST44). If the resulting value of N 
is equal to or less than 17, the sequence of the processes of ST40-ST44 is 
repeated while incrementing N by 1. 
If N exceeds 17 (YES in ST46), the average R data for the black reference 
stored in the memory 133 is read out first (ST48). Then, the average value 
of the R data for 17 pixels the white reference accumulated in the 
register in the arithmetic processor 132 is computed using the equation 
(2), and the computed average value (Rh) of the R data for white reference 
is compared with the average value (Rb) of the R data for the black 
reference read out from the memory 133 (ST50). This comparison is 
performed based on the equation (4) and the result is stored as data NR in 
the memory 133. 
The same process as done for the R data in ST36-ST50 will be executed for G 
data and B data (NO in ST51), and the comparison results are stored 
respectively as data NG and data NB in the memory 133. 
Upon completion of data comparison (equation (4)) for all the R, G and B 
data (YES in ST51), the data NR, NG and NB stored in the memory 133 are 
evaluated by the arithmetic processor 132. When the arithmetic processor 
132 finds that even one of the data NR, NG and NB is smaller than a 
predetermined value (e.g., 0.6), it discriminates that the life expiration 
of the lamp 23 has reached. 
When the arithmetic processor 132 discriminates that such is the case, it 
sends an error signal to the main controller 81 (ST52). Upon reception of 
the error signal, the main controller 81 sends, for example, a flicker 
signal to the display element (48.sub.7) on the manipulation panel 6 
(ST54), thereby flickering this element. Flickering the display element 
informs a user that the life expiration of the lamp has reached (ST56). 
The software illustrated in FIG. 14 discriminates the life expiration of 
the lamp in use with a high accuracy when the sensor 30 in FIG. 13 detects 
two or more pixel data. 
If the sensor 30 is a simple photosensor having a resolution for one pixel, 
the software run by the arithmetic processor (CPU) 132 in FIG. 13 may be 
simplified as shown in FIG. 15. 
First, R, G and B data are obtained using the black reference plate (ST60), 
and the attained R, G and B data are respectively written in the RAMs 
131R, 131G and 131B. Upon completion of data writing (YES in ST62), the 
operation enters a RAM read mode (ST64). In RAM read mode, it is 
determined from which one of the R, G and B RAMs data should be read out 
(ST66). In accordance with the decision, data of the individual color 
components for the black reference (corresponding to Rb, Gb and Bb in the 
equation (4)) are read out in the sequence of R, G and B, for example 
(ST68). 
Similarly, R, G and B data are obtained using the white reference plate 
(ST70), and the attained R, G and B data are respectively written in the 
RAMs 131R, 131G and 131B. Upon completion of data writing (YES in ST72), 
the operation enters a RAM read mode (ST74). In RAM read mode, it is 
determined from which one of the R, G and B RAMs data should be read out 
(ST76). In accordance with the decision, data of the individual color 
components for the black reference (corresponding to Rb, Gb and Bb in the 
equation (4)) are read out in the sequence of R, G and B, for example 
(ST78). 
When the R, G or B data for the black reference (Rb, Gb or Bb) and R, G or 
B data for the white reference (Rh, Gh or Bh) are read out, these data are 
compared with each other using the equation (4) (ST80). 
Upon completion of the data comparison for all the R, G and B data (YES in 
ST82), if it is found that even one of the data NR, NG and NB (equation 
(4)) is smaller than a predetermined value (e.g., 0.6), an error signal 
informing the expiration of the lamp's life is sent to the main controller 
81 from the arithmetic processor 132 (ST84). Upon reception of the error 
signal, the main controller 81 sends a flicker signal to the display 
element (48.sub.7) on the manipulation panel 6 (ST86). This flickers this 
element to thereby inform a user that the life expiration of the lamp has 
reached (ST88). 
The foregoing description has been given with reference to a case where 
light obtained using the white and black reference plates is separated 
into three primary color components R, G and B (or C, M and Y in 
complementary color relation with R, G and B). 
According to the present invention, however, the life expiration of the 
lamp can be discriminated using a luminance signal (I or J) obtained by 
combining the three primary color data. In other words, the luminance 
signal (I) obtained from the R, G and B data using the relation given in 
the following equation (5) or the luminance signal (J) obtained from the 
C, M and Y data using the relation given in the following equation (6) are 
actually measured with respect to the white reference plate. 
##EQU5## 
where K1-K3 are matrix coefficients for the RGB system while K4-K6 are 
matrix coefficients for the CMY system. 
When the luminance signal (I or J) is quantized by 8 bits, the life 
expiration check data NI or NJ is given by the following equations. 
EQU NI=I/256 (7 ) or 
EQU NJ=J/256 (8) 
If NI in the equation (7) or NJ in the equation (8) falls below a 
predetermined value (e.g., 0.6), it is discriminated that the life 
expiration of the lamp has reached. 
FIG. 16 illustrates the basic operations of the main controller 81 and 
sub-controllers 82 and 83 as shown in FIG. 1. 
When the apparatus shown in FIG. 1 is activated (ST100), initialization 
(ST102) for the main controller 81, initialization (ST202) for the 
sub-controller 82 and initialization (ST302) for the sub-controller 83 
start. 
Upon completion of these initializations, various initial statuses are set 
to the main controller 81 through the manipulation panel 6 in FIG. 12 
(ST104). Predetermined parameters for image processing are set in 
accordance with the set initial statuses (ST106). 
In parallel to this processing (ST102-ST106) of the main controller 81, the 
sub-controller 83 after the initialization (ST202) confirms the initial 
statuses of various switches on the manipulation panel 6 (ST204). 
Predetermined initial setting is executed to the printer section (93-96; 
51) in accordance with the confirmed initial statuses (ST206) and setting 
of the printer section is then completed (ST208). 
In parallel to this processing (ST102-ST106) of the main controller 81, the 
sub-controller 82 after the initialization (ST302) executes predetermined 
initial setting of the manuscript reader (80, 90, 25, 91, 92) (ST304) and 
setting of the manuscript reader is then completed (ST306). 
Upon completion of setting of the parameters for image processing (ST106), 
setting of the printer section (ST208) and setting of the manuscript 
reader (ST306), the main controller 81 confirms checks if the setting 
operations by the sub-controllers 82 and 83 have been accurately done 
(ST108), and then waits for the copy start key to be pressed by the user 
(ST110). 
As described above, the life expiration of the lamp 23 can accurately 
discriminated by reading a change in the ratio of the R, G and B 
components due to the usage and deterioration of the lamp 23. This always 
permits the use of the illumination lamp 23 having the ideal balance 
between the R, G and B components, thus ensuring a stable color 
reproducibility. 
The means for detecting the R, G and B components of light from the 
illumination lamp 23 is not restricted to a simple photosensor 30, but may 
be a CCD line image sensor or a two-dimensional CCD image sensor. The 
filter section 29 may be disposed on such portion of the optical path of 
the photoelectric converter 25 for reading the image of an original as to 
avoid interference with the image reading, so that the life expiration of 
the lamp 23 can be discriminated using the output of the photoelectric 
converter 25. 
The filters for separating color components of light from the illumination 
lamp 23 are not restricted to R, G and B types but may be C, M and Y 
filters as well. 
Although the life expiration of the lamp is discriminated by computation 
(software) conducted by the main controller 81, the discrimination is in 
no way limited to this particular type. For instance, a change in white 
balance due to deterioration of the lamp may be discriminated by hardware 
such as a gate array or an analog circuit which executes the processing 
corresponding to the mentioned computation. 
Although the foregoing description has been given with reference to a 
thermal color copying machine as an example of an image forming apparatus, 
the present invention can apply to an electronic copying machine, a 
facsimile and a video printer as well. The present invention may also 
apply to other apparatuses, such as an ink jet printer, a laser printer, a 
bubble jet printer, a dot impact printer and a silver-salt photographic 
apparatus. 
Further, a buzzer may be provided on the main body of the apparatus to 
inform a user of the expiration of the lamp's life. 
The present invention may be modified in various manners without departing 
from the scope of the invention. 
As described above, the present invention can provide an image forming 
apparatus which can accurately discriminate the life expiration of a light 
source to thereby improve color reproducibility. 
While the invention has been described in connection with what is presently 
considered to be the most practical and preferred embodiment, it is to be 
understood that the invention is not limited to the disclosed embodiment, 
but, on the contrary, is intended to cover various modifications and 
equivalent arrangements included within the scope of the appended claims, 
which scope is to be accorded the broadest interpretation so as to 
encompass all such modifications and equivalent arrangements.