JPS61285868A - Data compressing system for variable density picture - Google Patents

Abstract

PURPOSE:To obtain the high compressing ratio by separating the information to show whether the picture element is colored or uncolored and the information to show the density, compressing the former with the coding method and compressing the latter by removing the meaningless uncolored information. CONSTITUTION:A picture scanning device 1 decomposes the picture into the picture element, and converts variable density to an analog electric signal (a). A digital signal (b) converted by an A/D converting device 2 is '0' when the picture element is white by four bits and when it is black, obtains the value of 1-F according to the density. A binary circuit 3 generates a binary picture signal (c) which is '0' when a digital signal (b) is '0', and is '1' when the signal is 1-F. A coding circuit 4 codes the binary picture signal (c) to the compressing code and generates compressed data (d). A memory circuit 5 stores the value of a digital signal (b) only when the binary picture signal (c) is '1'. The value written in the memory circuit 5 shows the density of the picture element. A selecting circuit 6, first, selects the compressed data (d), sends to a data bus (f), next, selects density data (e) and sends to the data bus (f).

Description

[Detailed description of the invention] Industrial applications The present invention relates to a data compression method for one image, and particularly to a data compression method for one image.

The present invention relates to a data compression method for a grayscale image in which the pixels constituting the image have a plurality of different densities.

Conventional technology Conventionally, as data compression methods for this purpose, there are two methods: one in which the density of one pixel is expressed as a sub-matrix containing a certain number of pixels, and then it is compressed. well known.

Problems to be Solved by the Invention However, among the conventional data compression methods mentioned above,
The former can only handle pixels with multiple densities1.
Since much of the information regarding the density of the pixel is lost because it is expressed using pixels, there is a problem with image reproducibility.
The disadvantage is that the compression rate decreases in proportion to the number of pixel gradations.

The present invention has been made in view of the above-mentioned conventional circumstances, and
SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a new data compression method capable of overcoming the above-mentioned drawbacks inherent in the prior art.

Means for Solving the Problems In order to achieve the above object, the data compression method according to the present invention uses "θ" as If at least l bits are "θ", "a λ value conversion circuit that generates In, an encoding circuit that compresses and encodes the output signal of the λ value conversion circuit, and an output signal of the λ value conversion circuit is 1". The device is configured to include a writable/readable memory circuit capable of storing the value of the n-bit digital signal for at least one scanning line of pixels only when .

Embodiment Next, a preferred embodiment of the present invention will be specifically explained with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention. In FIG. 1, an image scanning device 1 decomposes an image into pixels and converts the shading of the pixels into an analog electrical signal aK by photoelectric conversion. The A/D converter converts the analog electrical signal a into a digital signal. In this embodiment, the number of density gradations is assumed to be l.

Then, the digital signal will be 0 (hexadecimal) if the pixel is white in Hirobit, and if it is black, it will be 0 (hexadecimal number), and if it is black, it will be 0 (hexadecimal number), and if it is black, it will be 0 (hexadecimal number), and if it is black, it will be 0 (hexadecimal number).
It takes a value in hexadecimal). λ value conversion circuit? is a digital signal, but if O (/A base), @, s (binary), /-
F(la) If it is a binary number, it generates a λ value image signal C which is @/''' (binary number).The encoding circuit DA generates a λ value image signal C
is encoded into a compression code such as a modified Huffman code to generate compressed data d. The memory circuit 3 is a writable/readable memory having a storage capacity equal to at least twice the number of pixels for one scanning line, and the λ value image signal C is @
The value of the digital signal is stored only in the case of l# (-base number). Since the value written in the memory circuit 3 represents the density of the pixel, it will be referred to as density data. The selection circuit 6 first selects the compressed data d for each scan of the image scanning device l.
is selected and the compressed code for one scanning line is sent to the data bus f to the storage device 7, and then the density data e is selected and the density data for one scanning line is sent to the data bus f to the storage device 7. Send. The storage device 7 stores data generated on the data bus f.

Next, the signals in FIG. 7 will be explained using FIGS. ω to (e). FIG. 2(a) is a diagram showing an example of an image.

- Scanning is for empty pixels, and there are black pixels around /Lt pixel and C pixel. FIG. 1(b) shows the digital signals for each pixel at this time arranged at the scanning head. The λ value converting circuit 3 converts the digital signal o(tt, base number)
If it is °O'' (binary number), if t-F (/l, base number), -, n (binary number) will be generated, but the value image damage signal C will be generated. FIG. 1(c) shows the digital signal C converted into an A-value image signal C. The encoding circuit encodes the A-value image signal C into a compression code, and here a modified Huffman code is used. FIG. 2(d) represents compressed data d obtained by 1,000-day human encoding of the λ-value image signal C in FIG. 2(C). In Fig. 1(e), the value of the digital signal S in Fig. 2(b) is selected by the λ value image signal C of the Fig. U signal (c). This is the density data e stored in the storage circuit 3.The density data in FIG. 2(e) includes 0, which serves as an identification code indicating the end of the density data for one scanning line. .

In this embodiment, the memory circuit for storing the density data is pixel-scanning line segment, but if a memory circuit for one image/page is provided, after storing the compressed data for the image in the memory device/
An example of storing density data for an image in a storage device is also conceivable.

2. Since the individual blocks in this embodiment are generally well known, detailed explanation will be omitted.

As described in detail, according to the present invention, information representing whether a pixel is colored or colorless is separated from information representing density, and the former is encoded using a well-known encoding method. The latter is compressed by removing meaningless colorless information, resulting in the effect that a higher compression rate than before can be obtained without losing any density information of the original image.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIGS. 2(a) to 2(e) are diagrams showing specific examples of the signals shown in FIG. 7.

Claims (1)

[Claims] In an image input device such as a facsimile or scanner that can convert a plurality of different densities of pixels constituting an image into an n-bit digital signal, the n-bit digital signal is used as an input signal and the n-bit digital signal is all "0". If so, “0”; if at least 1 bit is not “0”, “
a binarization circuit that generates "1", an encoding circuit that compresses and encodes the output signal of the binarization circuit, and the n-bit digital signal when the output signal of the binarization circuit is "1". 1. A data compression method for a grayscale image, comprising a writeable/readable memory circuit capable of storing values of at least one scanning line of pixels.