The present invention relates to an image input apparatus connected to another apparatus via a bus, and particularly to an image input apparatus which reads a manuscript image to transfer it to another apparatus.
The image input apparatus such as an image scanner is connected via a bus to other apparatus such as a higher-level apparatus of a computer, and reads a manuscript image such as a picture, a photograph and a document to transfer the read image data to the other apparatus. The transfer of the image data is performed by use of a parallel interface such as Centronics-conformable interface and SCSI (Small Computer System Interface) or a serial interface such as RS-232C and RS-422.
In the communication systems using these interfaces, the asynchronous communication is performed. When the communication is performed with another peripheral equipment connected to these interfaces, the image scanner makes the mediation for securing the right to use the bus each time it transmits or receives data. After acquiring the right to use, an output of a command and like and a response of a computer thereto are performed.
FIG. 11 is a timing chart of an image transfer in an image scanner using a conventional communication system.
First, the computer transfers to the image scanner the setting data for the reading conditions such as the size of the manuscript image and the reading resolution. The image scanner sends OK to the computer after receiving the setting data and finishing the setting of the units. Upon receiving it, the computer outputs a reading-start command to the image scanner. When receiving this reading-start command, the image scanner sends OK to the computer and starts to read the image.
The image scanner reads each line of the manuscript image by use of a reading unit, and stores it in a memory one by one. At this time, in the case of the image scanner using an automatic draft feeder (ADF), it is very difficult to halfway stop the sheet which is being automatically fed. Also, in the case of a flat head (FB) type image scanner, halfway stopping the reading operation will cause a shift in that part of the sheet, so that the read image has stripes. Therefore, once the manuscript image starts to be read, the reading operation cannot be stopped until one sheet of manuscript image is finished to read.
The computer requests the image scanner to transfer the read image data. The image scanner responds to this request to transfer the image data, which is stored in the memory, to the computer via the interface. When the image data is transferred to the computer, it is necessary to secure the right to use the bus each time the computer sends to the transfer request, and thus the image data cannot be transferred with a constant period.
Therefore, when the image scanner cannot secure the right to use the bus for the image data transfer, it takes time for the image data to be completely transferred. As a result, the image scanner needs a memory having a capacity capable of at least storing image data of one-sheet image. Thus, it is a neck to provide this memory when we consider reducing the cost of the image scanner (the first problem).
In addition, when the sheets of manuscript image are automatically fed by the ADF, command data indicating the end of reading each manuscript sheet is transferred to the computer each time one sheet of manuscript image is read out. Then, the image data is again transferred in response to the transfer request from the computer. At this time, since time is necessary to secure the right to use the bus if the bus is busy, the next sheet of manuscript image cannot be started to read.
When a plurality of sheets of manuscript are continuously fed and read, it is necessary to shorten the intervals at which the sheets are read, in order to speed up the processing. If one of the sheets cannot be started to read when the bus is busy, the processing speed cannot be increased. Moreover, if a large memory is provided enough to store the image data of all sheets of manuscript, all image data can transferred at a time. However, the larger the number of sheets is read, the larger the memory capacity becomes (the second problem).
In addition, when the image scanner cannot secure the right to use the bus for data transfer, time is taken for the image data to be completely transferred. Moreover, error checking is performed when the transferred image data is transmitted and received. If error is caused, the image data is again transferred. In other words, since the reading process is not intermitted even when the image data is again transmitted, the read image data is accumulated on the image scanner side.
The result is that the image scanner is required to include a memory having a capacity capable of storing the image data corresponding to at least one sheet of manuscript. Therefore, it is again a neck to provide this memory when we consider reducing the cost of the image scanner (the third problem).