Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2002-08-02
2004-02-24
Nguyen, Thinh (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S015000
Reexamination Certificate
active
06695434
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an image processing apparatus, an image printing apparatus, a control method of these apparatuses, a printer driver, and a storage medium and, more particularly, to an image processing apparatus, an image printing apparatus, a control method of these apparatuses, a printer driver, and a storage medium by which, in an image printing apparatus for processing color images, the volume of image data can be reduced by determining the number of gray levels of each color from the possible memory capacity and the data amount to be transferred, and, for a compressible color, by compressing image data to be transferred beforehand by a printing processor.
BACKGROUND OF THE INVENTION
For example, when a printer such as an inkjet printer by which the number of gray levels which can be output is extremely limited is to be used, the number of gray levels of image data is converted into the number of gray levels expressible by the printer by quantization performed by a printer driver on a host computer. After that, the image data is transferred from the host computer to the printer.
However, along with a recent increase in resolution of printers, the amount of image data to be transferred increases, and this increases the time required to transfer image data from a host computer to a printer. This may lead to a decrease in printing throughput.
To solve this problem, a density pattern method is used. That is, a printer driver on a host computer sends only tone information of the density pattern to a printer. The printer converts the received density pattern tone information into a dot pattern.
In this method, the host computer does not directly transfer binary data to the printer but transfers only tone information of the density pattern. This reduces the data amount to be transferred.
For example, assuming that the resolution of a printer is 1,200 dpi and the density pattern is formed every four dots, i.e., two in each of vertical and horizontal directions, which are output from the printer, five gray levels can be expressed as shown in FIG.
6
.
That is, the printer driver performs 5-valued quantization for 600-dpi pixel information. For quantization errors generated by this quantization, dot area modulation represented by error diffusion is performed.
The printer driver performs this processing before sending binary data directly to the printer, and transmits only the quantized tone in formation to the printer. By this processing alone, a continuous-tone image can be output to the printer in a pseudo manner. This reduces the data amount transferred from the host computer to the printer, and makes it possible to express a continuous-tone image without deteriorating the image quality.
To transfer image data from the host computer to the printer by using the density pattern method described above, the above-mentioned 5-valued quantized data is expressed by a quantized code having a predetermined bit length. This quantized code is then packed and transferred.
In connection with this packing process, the bit length of the quantized code is, e.g., two bits, four bits, or eight bits (since the data transfer unit is eight bits or sixteen bits). For 5-valued quantized data, a 4-bit quantized code is used.
In the case of 5-valued quantized data, therefore, tone information containing only five of sixteen values as a maximum number of gray levels expressible by four bits is used (the eleven remaining values are unused). This results in very redundant information.
Even this highly redundant information which expresses five gray levels by four bits poses no problem, if a somewhat low data transfer rate is permissible or if the printer has a large memory capacity. However, if the printer is to print data with high resolution at high speed or if the memory capacity of the printer must be reduced in order to reduce the cost of the printer, the data transfer rate or the data amount storable by the printer is important.
That is, it is very inefficient to transfer to the printer highly redundant information which expresses five gray levels by four bits.
To avoid this problem without changing the unit density pattern, it is possible to reduce the number of gray levels from five to four, thereby reducing the number of bits of the quantized code to two. However, reducing the number of gray levels causes discontinuous gray levels, forms pseudo contours, or increases graininess, thereby undesirably lowering the quality of the output image.
To solve the above problem, the prevent inventors disclosed another technique in Japanese Patent Laid-Open No. 2001-69358. This disclosure is related to a compression process which packs 12-bit data formed by gathering 5-valued, 4-bit data of three pixels into eight bits. This compression process can reduce the redundancy of an information amount without deteriorating the image quality.
Unfortunately, a problem sometimes arises when the above compression process is applied to a 6-color ink system which is used in recent high-quality inkjet printers to achieve high image quality.
That is, in this 6-color ink system aiming at high image quality, each ink color must be processed with an optimum number of gray levels.
This will be explained with reference to
FIGS. 7A
to
7
C. The 6-color ink system for achieving high image quality uses inks of four colors, i.e., yellow, magenta, cyan, and black, and, in order to increase the number of gray levels, uses inks of two other colors, i.e., light cyan and light magenta lighter than cyan and magenta, respectively. Yellow, magenta, cyan, black, light cyan, and light magenta will be respectively referred to as Y, M, C, K, LC, and LM hereinafter. Also, light cyan and light magenta will be generally called light inks, and cyan ink and magenta ink darker than light cyan and light magenta will be generally called dark inks.
FIG. 7A
shows an example of the relationship between the input signal and the ink discharge amount in a tone generating system using both light ink (LC or LM) and dark ink (C or M).
FIG. 7A
also shows an example of the relationship between the input signal and the ink discharge amount when only light ink (LC or LM) is used.
As shown in
FIG. 7A
, assuming that the ink discharge amount when one dot is formed at a resolution of 1,200 dpi is 100%, the following discharge amount characteristic is used. That is, as shown by a light ink discharge amount characteristic
1
indicated by the dotted line, the light ink alone is used until 100%. As shown by a dark ink discharge amount characteristic
1
indicated by the alternate long and short dashed line, the dark ink begins to be discharged when the light ink reaches 100%. The discharge amounts of the light ink and dark ink are gradually reduced and increased, respectively, and finally the dark ink reaches 100%.
Assume that ink discharge amounts of 80 to 100, 60 to 80, 40 to 60, 20 to 40, and 0 to 20% of the light ink or dark ink explained above correspond to 4 dots, 3 dots, 2 dots, 1 dot, and 0 dot, respectively, shown in
FIG. 6
, and that the dark ink density is twice the light ink density. In this case, nine gray levels from 0 to 8 shown in
FIG. 7B
can be expressed by controlling the discharge amounts of the light ink and dark ink as represented by the light ink discharge amount characteristic
1
and the dark ink discharge amount characteristic
1
shown in FIG.
7
A.
Note that this example shown in
FIG. 7A
is merely an example, so the characteristics can also be nonlinear ones rather than linear ones as shown in FIG.
7
A. Also, the characteristics can change in accordance with hue. Furthermore, the ratio of the dark ink density to the light ink density need not be twice and can be appropriately changed.
No problem arises when the density balance between the dark ink density and the light ink density is satisfactory (in the above example, when the dark ink density is accurately controlled to be twice the light ink density), and so the start of dark ink discharge is inconspicuous. However, if the light ink is much l
Kawatoko Norihiro
Konno Yuji
Masuyama Atsuhiko
Ogasahara Takayuki
Tajika Hiroshi
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