JPH088640B2 - Image input device - Google Patents

Description

The present invention relates to a technique for improving the input characteristics of a halftone image in an image scanner used for desk top publishing or the like.

[Conventional technology]

As image sensors used in image input devices, various types of tubes and semiconductors are used, but none of them have a perfect one-to-one correspondence between the amount of received light and the sensor output, and the received light called by the name of gamma characteristic has been used in the past. There was a non-linear relationship between quantity and sensor output. This gamma characteristic has a slightly different property in each component even if it is the same kind of sensor or the same kind of sensor, and in the image input device composed of a plurality of image sensors which is the object of the present invention, the difference in gamma characteristics between the respective sensors. Exists. Due to the difference in gamma characteristics between multiple image sensors, even if each sensor output is set so that the same output is output at the reference white level, when a gray original that is a halftone image is input, A difference occurs in the output of each sensor, and the data corresponding to the same gray cannot be obtained. In order to correct the gamma characteristic, there is a method in which the gamma characteristic of each image sensor forming the image input device is first measured and then normalized by a corresponding correction curve so that the respective outputs are equalized.
According to this method, it is necessary to measure the characteristics of each image sensor before assembling the apparatus and individually manage the characteristics, resulting in an increase in manufacturing cost.

Image sensor technology relating to the present case includes, for example, Japanese Patent Application Laid-Open No. 61-161580.

[Problems to be Solved by the Invention]

The conventional technology has the above-mentioned problems. An object of the present invention is to improve the deterioration of the image quality which causes a difference in the output of each sensor when a uniform halftone image is input due to the difference in the gamma characteristic of each image sensor in the image input device composed of a plurality of image sensor elements. is there. In particular, when correcting the gamma characteristic, it is an object to perform automatic correction prior to the original document image input without actually reading a document with halftone density.

[Means for solving the problem]

As a method of correcting the gamma characteristic of an image sensor used in an image input device, the present invention provides a circuit and program for measuring the gamma characteristic of each of a plurality of image sensor elements used prior to the original image input of an original. Is prepared, and a correction curve corresponding to each image sensor is calculated and associated with these.

When inputting the image data of the actual form, the output of each image sensor is normalized through the correction curve, so that even when a halftone image is input, it can be input as uniform data.

For the measurement of gamma characteristics, it is general to read a white paper representing a white level that should originally serve as a reference and a gray paper representing each halftone, but in the present invention, the reference reflector is used as a reference scan cycle. The reference output corresponding to the white level is obtained by reading. In order to change the light amount corresponding to the halftone, the fact that the image sensor output corresponds to the received light amount × scan period (exposure time) is used, and instead of changing the received light amount, the scan period is changed. For example, a sensor output corresponding to giving a light amount of 1/2 is obtained by making the light amount the same and halving the scan cycle. By utilizing this phenomenon, the sensor output when the light amount is 1 / a can be obtained with a cycle of 1 / a. In this way, the sensor output corresponding to the reference white level and the sensor output corresponding to the halftone can be obtained, and the gamma correction curve is calculated for each image sensor element based on these data.

[Action]

The equivalent light quantity changing function by changing the scan cycle of the image sensor, which is a feature of the present invention, is composed of an integrated circuit and a simple software program. A counter circuit is used as the scan cycle to generate a cycle corresponding to the reference cycle and the 1 / a cycle. The counter is usually a digital quantity counter, and N / M (M and N are integers) is equivalent to 1 / a.
To achieve the value If N and M are set to large values, N / M can approach 1 / a without limit. By creating a scan cycle equivalent to 1 / a by selecting N and M, it means that the image sensor could be set to a light amount of 1 / a, and by converting the image sensor output to A / D, the light amount can be changed. The sensor output value corresponding to 1 / a is obtained. The value of a (actually M,
The software program determines the appropriate gamma characteristic of the corresponding sensor by taking several points.
A software program calculates a curve for correcting this gamma characteristic and prepares it in the memory circuit. By using this in-memory correction curve, the gamma characteristic of each image sensor element is corrected and all image sensor elements output the same output even when a halftone image is input.

〔Example〕

An embodiment of the present invention will be described below with reference to screens.

In FIG. 1, 1 is an image sensor consisting of a plurality of chips (contact type or reduction type is acceptable), 2 is an amplifier for amplifying the image sensor output, and 3 is an output of the amplifier 2.
A / D converter for A / D conversion, 4 is 1 of the image sensor 1
A line memory that stores the output obtained by A / D converting the scan output by the A / D converter 3 and a line memory address generator 5 that generates an address when the output of the A / D converter 3 is written to the line memory 4. , 6 is a processor (CPU) for calculating the contents of the line memory 4 and selecting a gamma correction curve, 7-1 to 7-N are latches for which the gamma correction curve number is set from the CPU 6, and 8 is a latch 7-. Read-only memory (RO) for gamma correction of the image sensor output by the output from 1 to 7-N
M) and 9 are setting the scan cycle of the image sensor 1, outputting the pixel clock to the line memory address generator 5, outputting the conversion clock to the A / D converter 3, and enabling the outputs to the latches 7-1 to 7-N. A scan timing generator that outputs a signal, and 10 is a binarization circuit that binarizes multivalued data that has been gamma-corrected by the ROM 8.

Next, the operation of this embodiment will be described with reference to FIGS.

First, as shown in FIG. 2, the reason why the read density changes for each chip due to the difference in the sensitivity characteristic (gamma characteristic) of each chip of the sensor 1 will be described. Fig. 2 (a)
Indicates the sensor output (amplifier output) when reading a white original. Normally, in this state, the gain of the amplifier 2 is changed for each chip and adjustment is performed so that the output levels of all the chips match, so that the output of the sensor 1 (output of the amplifier 2) becomes flat. FIG. 2B shows the output (amplifier 2 output) of the sensor 1 when a halftone (gray) original is read after such adjustment. Since each chip has different sensitivity characteristics, Causes a step. The occurrence of this step means that the read density differs for each sensor chip. Note that FIG. 2 is a diagram showing a state in which the outputs of a plurality of sensor chips are serially output and operated as if they were a one-chip sensor.

FIG. 3 is a diagram showing the relationship between scan synchronization and sensor output. FIG. 3 (a) shows the sensor output at the time of scan synchronization T _W , and FIG. 3 (b) shows the time at the time of T _W / 2. FIG. 3 (c) shows the sensor output, and the sensor output at T _W / 3. Since the image sensor output corresponds to (amount of received light) x (scan synchronization), if the amount of received light is constant, the sensor output changes by changing the scan cycle, and if scan synchronization is set to 1/2, 1/3 The sensor outputs are 1/2 and 1/3, respectively, as shown in FIGS. 3 (b) and 3 (c). The step generated at this time is due to the difference in the sensitivity characteristics of the sensor chips. In other words, FIGS. 3 (b) and 3 (c) show the same sensor output when the amount of received light is 1/2, 1/3 (when a halftone original is read), and It shows that the sensitivity characteristic of the sensor can be known by changing the scan synchronization without reading the original.

Next, the operation of the image input device shown in FIG. 1 will be described with reference to FIG. First, the scan timing generator 9 determines the scan cycle of the image sensor 1.
Set to T _G1 (T _G1 <T _W ), and write the data digitally converted by the A / D converter 3 to the line memory 4. Before the above operation, as explained in FIG. 2, the output level of the sensor (output level of the amplifier 2) is adjusted to the same level by the gain adjustment of the amplifier 2 during the scan cycle T _W. Be present. After that, the CPU 6 reads the contents of the line memory 4, samples a predetermined number of data for each sensor chip, and obtains the average of the sampling data for each chip to obtain the output level of each chip. Next, the scan timing generator 9 sets the scan cycle of the image sensor 1 to T
_G2 , T _G3 … T _GN (T _GN … <T _G2 <T _G1 <T _W ) is set and the same processing as above is performed, and the sensor output level for each scan timing is calculated, and the sensitivity characteristics for each sensor chip are calculated. . The setting of scan synchronization is performed by the control signal from the CPU 6. Thereafter, the CPU selects a curve for correcting this sensitivity characteristic from the curves shown in FIG. 4 based on this sensitivity characteristic and outputs the number of this curve to the latches 7-1 to 7-N in binary (1 to N corresponds to the sensor chip number.). The outputs of the latches 7-1 to 7-N are connected by wired OR to the upper address of the ROM 8 having the built-in sensitivity correction curve, and the output is the chip from the scan timing generator 9 shown in FIG. 2 (c). Select signals 7-1a, 7-2a ... 7-
Sequentially enabled by Na. The output of the A / D converter 3 is connected to the lower address of ROM8.
The data before sensitivity correction is input. As described above, the sensitivity correction is performed for each sensor chip, and the step of the sensor output level as shown in FIG. 2B can be eliminated at the time of reading the halftone original, and the read density is made the same for each chip. be able to.

The above is one embodiment of the present invention, but as another embodiment, a plurality of correction data are obtained by the above method, a correction curve is created by an interpolation algorithm under the program control in the CPU 6, and the correction curve is stored in a RAM. Stored in memory such as R,
If this RAM is used instead of the OM8, the sensor output can be corrected without preparing a correction curve in the ROM beforehand.

Further, in the above embodiment, the correction curve is switched for each sensor chip and correction is performed so that the sensor output level becomes the same level, and then the binarization circuit 10 binarizes the outputs of all the sensor chips at the same slice level 10a. However, instead of correcting the sensor output level to the contrary, by creating a correction curve of the slice level 10a in the same manner as the above embodiment, by switching the correction curve of the slice level 10a for each chip, It is possible to obtain the same effect as that of the above embodiment.

Further, instead of the image sensor 1, by incorporating the entire portion excluding the binarization circuit 10 in FIG. 1 as one image sensor, the above correction can be performed inside the image sensor, and the sensor can be read at the time of reading a halftone original. It is possible to make the output levels the same.

〔The invention's effect〕

According to the present invention, since the sensitivity characteristic of each image sensor can be corrected, the reading density of each sensor becomes the same at the time of reading a halftone original, and there is an effect of improving deterioration of image quality. Further, in correcting the sensor sensitivity characteristic, it is not necessary to actually read the halftone original, so that the operability is greatly improved.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing a sensor output at the time of reading a halftone original, FIG. 3 is a diagram showing a relationship between scan synchronization and sensor output, and FIG. FIG. 5 is a diagram showing a correction curve of the sensor sensitivity characteristic, and FIG. 5 is a diagram showing the relationship between the sensor output and the slice level. 1 ... Image sensor, 2 ... Amplifier, 3 ... A / D converter, 4 ... Line memory, 5 ... Line memory address generator, 6 ... CPU, 7-1 to 7-N ... Latch, 8 ...... RO
M, 9 …… Scan timing generator, 10 …… Binarization circuit

Claims (3)

[Claims] 1. An image input device having an image sensor composed of a plurality of chips, wherein a means for changing a scan cycle of the image sensor, and a sensor output corresponding to the cycle change under a constant light receiving amount are provided for each chip. An image input device comprising: means for calculating a gamma correction curve for reading the sensor output for each chip; and means for correcting the sensor output for each chip based on the correction curve. 2. The image input according to claim 1, wherein a plurality of sensor outputs for each chip are obtained by changing the scan cycle, and a correction curve is calculated using an interpolation algorithm. apparatus. 3. An image input device having an image sensor composed of a plurality of chips, wherein a means for changing a scan cycle of the image sensor, and a sensor output corresponding to the cycle change under a constant light receiving amount are provided for each chip. And a means for calculating a gamma correction curve for correcting the binary slice level of the sensor output for each chip, and a means for correcting the binary slice level of the sensor output for each chip based on the correction curve. An image input device comprising: