JPH0126591B2 - - Google Patents
Info
- Publication number
- JPH0126591B2 JPH0126591B2 JP58182134A JP18213483A JPH0126591B2 JP H0126591 B2 JPH0126591 B2 JP H0126591B2 JP 58182134 A JP58182134 A JP 58182134A JP 18213483 A JP18213483 A JP 18213483A JP H0126591 B2 JPH0126591 B2 JP H0126591B2
- Authority
- JP
- Japan
- Prior art keywords
- pixel
- luminance signal
- value
- brightness
- read
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 238000000034 method Methods 0.000 claims description 10
- 238000013139 quantization Methods 0.000 claims description 8
- 230000006866 deterioration Effects 0.000 description 6
- 238000010586 diagram Methods 0.000 description 4
- 230000005540 biological transmission Effects 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 1
- 239000002131 composite material Substances 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 230000000007 visual effect Effects 0.000 description 1
Landscapes
- Facsimile Image Signal Circuits (AREA)
Description
産業上の利用分野
本発明は多値画像情報の符号化方法に関するも
のである。
従来例の構成とその問題点
中間調画像を走査読取りにより、画素に分割
し、この画素の振幅(輝度)を量子化し、かつ符
号数を減少させる際に、画素の読取り輝度範囲を
等間隔のレベルで分割し、各レベルにはそのレベ
ル範囲内を代表するレベル値を与える。そして当
該画素の読取り輝度値に前に処理された画素の残
余輝度信号を加算した合計値が、上記レベルのど
のレベルにあるかを判定し、当該画素の値をその
レベルを代表する値で表わし、上記合計値と代表
値との差を、当該画素より後に処理する画素に加
算することで、多値画像を量子化したときの符号
数を減ずる方法が従来よりある。
しかしこの方法では、レベルの分割が等間隔で
あるために、輝度の高い画像の部分と低い画像の
部分とで、画質劣化の程度が視覚的に同一でな
く、暗い部分において劣化が著しいという欠点を
有する。
発明の目的
本発明は、多値画像の輝度情報の符号化に際
し、1画素当りのビツト数を画質劣化を殆んど伴
わずに減少させることができ、また画質劣化の程
度は輝度の高い画像減も低い画像域も視覚的に殆
んど同一であるような多値画像情報の量子化方法
を提供するものである。
発明の構成
本発明は、画素がとりうる読取り輝度信号の範
囲を少なくとも2つの範囲が等しくないn個の区
域に分け、その区域にそれぞれの区域を代表する
区域代表値を設定し、輝度値を量子化しようとす
る画素(当該画素と呼ぶ)の読取り輝度値に、既
に量子化を終えた画素の残余輝度信号を加えた輝
度信号がどの区域内にあるかを判定し、当該画素
の量子化値をその区域の代表値とし、代表値と輝
度信号の差を、当該画素より後に処理する1個又
は複数個の画素の読取り輝度値に加算し、前述し
た区域を代表する代表値は、量子化した符号によ
つて表現することにより、上記目的を達するもの
である。また上述した間隔が等しくないn個の区
域の分割の仕方としては、輝度の少い部分では間
隔を細かく、輝度の高い部分では間隔を大きくす
ると、さらには間隔がおおよそその輝度区間の区
間代表値に比例すると、少い符号数で視覚的に自
然感の失われ方の少ない画像が得られる。
実施例の説明
以下に図面を用いて本発明の一実施例について
説明する。
第1図は本発明を用いたシステムのブロツク図
である。
上記の残余輝度信号の加算処理について以下に
具体的に説明する。
画面の水平方向に連続する4画素a,b,c,
dの輝度信号値を“135”とし、さらに輝度信号
の区域を下記表aのように設定した場合、
INDUSTRIAL APPLICATION FIELD The present invention relates to a method for encoding multivalued image information. Configuration of conventional example and its problems When dividing a halftone image into pixels by scanning reading, quantizing the amplitude (brightness) of these pixels, and reducing the number of codes, the reading brightness range of pixels is divided into pixels at equal intervals. Divide by level, and give each level a level value that represents the level range. Then, it is determined which of the above levels the total value of the read luminance value of the pixel and the residual luminance signal of the previously processed pixel is at, and the value of the pixel is expressed as a value representative of that level. There is a conventional method of reducing the number of codes when a multivalued image is quantized by adding the difference between the total value and the representative value to a pixel to be processed after the pixel in question. However, this method has the disadvantage that because the levels are divided at equal intervals, the degree of image quality deterioration is not visually the same between high-brightness image parts and low-brightness image parts, and the deterioration is significant in dark parts. has. Purpose of the Invention The present invention makes it possible to reduce the number of bits per pixel with almost no deterioration in image quality when encoding brightness information of multivalued images, and the degree of deterioration in image quality can be reduced when encoding brightness information of multilevel images. The object of the present invention is to provide a method for quantizing multivalued image information such that both image regions and low image regions are visually almost the same. Structure of the Invention The present invention divides the range of the read luminance signal that a pixel can take into n regions, at least two of which are unequal, sets a region representative value representing each region in each region, and sets the luminance value. Determine in which area the brightness signal obtained by adding the residual brightness signal of the pixel that has already been quantized to the read brightness value of the pixel to be quantized (referred to as the relevant pixel) is located, and then quantize the relevant pixel. value as a representative value of the area, and the difference between the representative value and the luminance signal is added to the read luminance value of one or more pixels processed after the pixel in question, and the representative value representative of the area mentioned above is determined by the quantum The above objective is achieved by expressing the information using converted codes. Furthermore, as a method of dividing the above-mentioned n areas with unequal intervals, the intervals can be made finer in areas with low brightness, and the intervals can be increased in areas with high brightness. When it is proportional to , an image with less loss of visual naturalness can be obtained with a small number of codes. DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a system using the present invention. The above-mentioned addition process of the residual luminance signal will be specifically explained below. Four consecutive pixels a, b, c, in the horizontal direction of the screen
When the luminance signal value of d is set to "135" and the luminance signal area is set as shown in Table a below,
【表】
何の処理も施さなければ、これらの4画素の輝
度信号は、代表値“128”で符号化され、4画素
全て“7”だけ実際より輝度の低い画像として画
像が劣化してしまう。[Table] If no processing is performed, the luminance signals of these four pixels will be encoded with a representative value of "128", and the image will deteriorate as the luminance of all four pixels is "7" lower than the actual image. .
【表】
そこで本発明においては、表bに示すように画
素aの輝度信号値と代表値の差分(残余輝度信
号)=“7”を画素bの輝度信号“135”に加算す
る。その結果、画表bは輝度信号値“142”とし
て区分けが行われる。画素cについても同様に画
素bの残余輝度信号=“14”が加算され、加算処
理後の輝度信号は“149”となり、その代表値は
“144”として符号化が行われる。
以上のように輝度信号値と代表値の差分である
残余輝度信号を近接する画素の輝度信号値に加算
することで、4画素の輝度信号値が“135”の画
像に対して、平均輝度信号値が“132”の画像と
して符号化される。すなわち上述の説明において
は、4画素の輝度信号値を全て“128”で代表す
るものに対して、画素cの輝度を“144”の区分
で代表する点で本例は異なる。人間の視覚によれ
ば隣接する画素の輝度は平均化して認識されるた
めに、差分を加算する本願の処理を施すことで、
より原画に近い劣化のない画像を実現できる。
1は走査読取装置で、これで読取つた画像のア
ナログ輝度信号を、後で詳細する量子化装置2で
量子化する。量子化装置2が本発明に係るブロツ
クである。3は磁気デイスクなどの記憶装置で、
量子化装置2で量子化された画像信号は、ここに
蓄えられ、必要に応じて読出される。4はデジタ
ルアナログ変換装置で、読出した量子化画像信号
をアナログ信号に変換し、記録装置5にて印画
し、原画を復元する。
なお、記憶装置5はフアクシミリの伝送線に置
き換えることもできる。この場合、走査読取装置
1及び量子化装置2は送信端末、デジタルアナロ
グ変換装置4及び記録装置5は受信端末となる。
次に第2図を参照して、本発明の一実施例にお
ける量子化方法について説明する。
第2図は、第1図に示した量子化装置2の詳細
なブロツク構成図である。
走査による読取輝度信号は線20を経て、加算
回路21に入力される。記憶回路22は、当該画
素より前に処理された画素からの残余信号のうち
当該画素に割りふられ、当該画素に加算すべき量
を記憶しておき、当該画素が必要とするときに、
その量を線23上に出力する。そこで加算回路2
1は、線20、線23の信号を加算して、輝度信
号を作り、線24上に出力する。判定回路25
は、輝度信号値が、どの区域にあるかを判定し、
判定結果を線26に区域代表値として線29に量
子化値として出力する。差分回路27は、線26
上の区域代表値と線24上の輝度信号値との差を
求め、これを線28を経由して記憶回路22へ送
る。そして前述したように記憶回路22は、当該
画素の残余輝度信号を、当該画素より後に処理さ
れる、1個又は複数個の画素に割り振る。割り振
る画素が1個のとき、当該画素の次に処理する画
素に、割り振る画素が2個のときは、当該画素の
次に処置する画素と、1走査線後で、当該画素と
同じ位置の画素に、ほぼ残余輝度の1/2ずつを割
り振るのは好ましい1例である。そして判定回路
25より線29に出力される量子化値は、第1図
の記憶装置3に送られる。
上述の処理を全画素に対して順次行なうことに
より、画素の読取り輝度信号がとりうる範囲を間
隔が等しくないn個の区域に分割し、そして前記
画素の読取り輝度信号に前に処理された画素の残
余輝度信号を加算して輝度信号となし、前記輝度
信号が前記区域のどれに入るかで量子化し、前記
区域の代表値と輝度信号の差である残余輝度信号
を、当該画素より後に処理される画素の読取り輝
度信号に加算することができる。
次に表を参照しながら、本発明の一実施例にお
ける量子化方法をさらに詳細に説明する。
第1表、第2表は区域の数がn=8の場合につ
いて、区域の分割例を説明したものである。[Table] Therefore, in the present invention, as shown in Table b, the difference between the luminance signal value of pixel a and the representative value (residual luminance signal) = "7" is added to the luminance signal "135" of pixel b. As a result, the screen b is divided into luminance signal values of "142". Similarly, the residual luminance signal of pixel b=“14” is added to pixel c, and the luminance signal after the addition process becomes “149”, and its representative value is encoded as “144”. As described above, by adding the residual luminance signal, which is the difference between the luminance signal value and the representative value, to the luminance signal value of adjacent pixels, the average luminance signal is It is encoded as an image with a value of “132”. That is, in the above description, the brightness signal values of all four pixels are represented by "128", but this example differs in that the brightness of pixel c is represented by "144". According to human vision, the brightness of adjacent pixels is perceived as being averaged, so by applying the processing of this application that adds the differences,
It is possible to create an image that is closer to the original image without any deterioration. Reference numeral 1 denotes a scanning reading device, and a quantizing device 2 quantizes the analog luminance signal of the image read by the scanning reading device. The quantizer 2 is a block according to the invention. 3 is a storage device such as a magnetic disk,
The image signal quantized by the quantizer 2 is stored here and read out as needed. Reference numeral 4 denotes a digital-to-analog converter which converts the read quantized image signal into an analog signal, which is printed by a recording device 5 to restore the original image. Note that the storage device 5 can also be replaced with a facsimile transmission line. In this case, the scanning reading device 1 and the quantization device 2 serve as transmitting terminals, and the digital-to-analog converting device 4 and recording device 5 serve as receiving terminals. Next, referring to FIG. 2, a quantization method in an embodiment of the present invention will be described. FIG. 2 is a detailed block diagram of the quantization device 2 shown in FIG. 1. The read luminance signal obtained by scanning is input to an adder circuit 21 via a line 20. The storage circuit 22 stores the amount to be allocated to and added to the pixel out of the residual signal from the pixel processed before the pixel, and when the pixel requires it,
Output that amount on line 23. Therefore, addition circuit 2
1 adds the signals on lines 20 and 23 to create a luminance signal and outputs it on line 24. Judgment circuit 25
determines in which area the luminance signal value is located,
The determination result is output on a line 26 as an area representative value and on a line 29 as a quantized value. The differential circuit 27 connects the line 26
The difference between the upper area representative value and the luminance signal value on the line 24 is determined and sent to the storage circuit 22 via the line 28. Then, as described above, the storage circuit 22 allocates the residual luminance signal of the pixel to one or more pixels that are processed after the pixel. When there is one pixel to be allocated, the pixel to be processed next after the pixel is allocated, and if there are two pixels to be allocated, the pixel to be processed next to the pixel and the pixel at the same position as the pixel after one scanning line. A preferable example is to allocate approximately 1/2 of the residual brightness to each of the following. The quantized value outputted from the determination circuit 25 to the line 29 is sent to the storage device 3 shown in FIG. By sequentially performing the above processing on all pixels, the range that the pixel read luminance signal can take is divided into n areas with unequal intervals, and the previously processed pixel The residual brightness signals of the pixel are added to form a brightness signal, the brightness signal is quantized depending on which area it falls into, and the residual brightness signal, which is the difference between the representative value of the area and the brightness signal, is processed after the pixel. It can be added to the read luminance signal of the pixel to be read. Next, the quantization method in one embodiment of the present invention will be explained in more detail with reference to the table. Tables 1 and 2 explain examples of dividing areas when the number of areas is n=8.
【表】【table】
【表】【table】
【表】
第1表においてコラムAは特定の読取り輝度値
は便宜上与えた番号であり、0〜14の15個の読取
り輝度値と関連づけられている。コラムBは読取
り輝度0を除く最低読取り輝度を1とし、読取り
輝度差の比を1.49とした場合の読取り輝度値の集
合である。このとき最高読取り輝度は173.27とな
る。なお輝度は物理量であり通常単位をもつが、
本実施例における説明では単位を省略し、量を数
値で示すこととする。コラムCはコラムBの値を
読取り、最高輝度を1.000で正規化した場合、ま
たコラムDはコラムBの値を最高読取り輝度を
255で正規化した場合である。区域の数nを8と
するとき、(2n−1)個の読取り輝度値を求め
る。両端の値および、その間の1個おきの値が区
域代表値であり、それの読取り輝度番号を〇印で
囲んで示す。
第2表においてコラムEは夫々の区域代表値に
与えた量子化値であり、2進表示のビツト数をm
とし、n=8のとき、2進表示ではm=3ビツト
で表わされ、区域の数が8の場合を示している。
コラムFは夫々の量子化値に対する読取り輝度値
の範囲である。
本実施例においては、画信号がとりうる読取り
輝度範囲の中から、値の順に(2n−1)個の読
取り輝度値を設定し、これに0より(2n−2)
までの番号を付与し、番号0および番号(2n−
2)は区域代表値であり、番号0の区域代表値
は、番号1以下の、また番号2の区域区代表値は
番号1〜番号3の読取り輝度範囲を代表するごと
くに、区域代表値と区域の関係が成立している。
なお区域代表値を必ずしも両端にとらなくても、
或る程度本発明の目的を達成するが、両端にとれ
ば本発明の目的を完全に達成することができる。
すなわち、一定の面積範囲で考えた全輝度量は、
符号数の減少にも拘らず変化しないということで
ある。なお、第1表、第2表においては、輝度
値、範囲はアナログ量としての表現であるが、本
発明では、区域のとり方は、アナログ量か、デジ
タル量かは問題ではない。第3表に、入力読取り
輝度信号がデジタル値のときの量子化値(コラム
e)と読取り輝度範囲(コラムf)の関係を示
す。[Table] In Table 1, in column A, specific read brightness values are numbers given for convenience and are associated with 15 read brightness values from 0 to 14. Column B is a set of read brightness values when the lowest read brightness excluding the read brightness of 0 is set to 1 and the read brightness difference ratio is set to 1.49. At this time, the maximum read brightness is 173.27. Note that brightness is a physical quantity and usually has units, but
In the description of this embodiment, units will be omitted and quantities will be expressed numerically. Column C reads the value of column B and normalizes the maximum brightness by 1.000, and column D reads the value of column B and calculates the maximum brightness.
This is the case when normalized by 255. When the number n of areas is 8, (2n-1) read brightness values are determined. The values at both ends and every other value between them are the area representative values, and their read luminance numbers are indicated by circles. In Table 2, column E is the quantization value given to each area representative value, and the number of bits in binary representation is m.
When n=8, m=3 bits in binary notation, and the case where the number of areas is 8 is shown.
Column F is the range of read luminance values for each quantized value. In this embodiment, (2n-1) reading brightness values are set in order of value from the reading brightness range that the image signal can take, and from 0 to (2n-2)
Assign numbers up to, number 0 and number (2n-
2) is the area representative value, and the area representative value of number 0 is the area representative value of numbers 1 and below, and the area representative value of number 2 is the area representative value, such that it represents the reading brightness range of numbers 1 to 3. A region relationship is established.
Note that the area representative values do not necessarily have to be taken at both ends.
Although the object of the present invention can be achieved to some extent, the object of the present invention can be completely achieved if taken at both ends.
In other words, the total luminance considered within a certain area range is
This means that it does not change despite the decrease in the number of codes. Note that in Tables 1 and 2, the brightness values and ranges are expressed as analog quantities, but in the present invention, it does not matter whether the areas are drawn in analog quantities or digital quantities. Table 3 shows the relationship between the quantized value (column e) and the read luminance range (column f) when the input read luminance signal is a digital value.
【表】【table】
【表】
なおコラムeは2進数表現、コラムfは10進数
表現である。読取り輝度番号に対応する読取り輝
度値としては、上述の如く、輝度値の差が等比的
な場合、そのほか必要に応じた適当な規則又は試
行により定めた値であつてよい。
また残余輝度信号の値又は符号によつて、合成
輝度信号値は、読取り輝度信号の最高値を越える
場合、負の値をとる場合も存在する。
発明の効果
以上本発明によれば、中間調をもつ写真などの
画像情報を少ない符号数で、劣化が少く量子化す
ることが可能となり、このため、画像の記憶に際
してはメモリー容量を減少させ伝送に際しては、
短時間伝送をすることができ、その効果は大き
い。[Table] Column e is a binary representation, and column f is a decimal representation. The read brightness value corresponding to the read brightness number may be, as described above, when the difference in brightness values is geometric, or it may be a value determined by an appropriate rule or trial as necessary. Furthermore, depending on the value or sign of the residual luminance signal, the composite luminance signal value may exceed the maximum value of the read luminance signal or take a negative value. Effects of the Invention According to the present invention, it is possible to quantize image information such as a photograph with halftones with a small number of codes and with little deterioration. Therefore, when storing an image, the memory capacity is reduced and the data is transmitted. In this case,
Transmission can be carried out in a short period of time, and the effect is great.
第1図は本発明の一実施例における多値画像情
報の量子化方法を実施するためのシステムのブロ
ツク図、第2図は量子化装置のブロツク図であ
る。
1……読取装置、2……量子化装置、3……記
憶装置、4……D/A変換装置、5……記録装
置、21……加算回路、22……記憶回路、25
……判定回路、27……差分回路。
FIG. 1 is a block diagram of a system for implementing a method for quantizing multivalued image information in one embodiment of the present invention, and FIG. 2 is a block diagram of a quantization device. DESCRIPTION OF SYMBOLS 1... Reading device, 2... Quantization device, 3... Storage device, 4... D/A conversion device, 5... Recording device, 21... Addition circuit, 22... Storage circuit, 25
...Judgment circuit, 27...Difference circuit.
Claims (1)
が等しくないn個の区域に分割し、そして前記画
素の読取り輝度信号に前に処理された画素の残余
輝度信号を加算して輝度信号となし、前記輝度信
号が前記区域のどれかに入るかで量子化し、前記
区域の代表値と輝度信号の差である残余輝度信号
を、当該画素より後に処理される画素の読取り輝
度信号に加算することを特徴とする多値画像情報
の量子化方法。1. Divide the range that the read luminance signal of a pixel can take into n areas with unequal intervals, and add the residual luminance signal of the previously processed pixel to the read luminance signal of the pixel to obtain a luminance signal; The luminance signal is quantized depending on whether it falls into any of the regions, and a residual luminance signal, which is the difference between the representative value of the region and the luminance signal, is added to the read luminance signal of a pixel processed after the pixel. Features a quantization method for multivalued image information.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP58182134A JPS6074772A (en) | 1983-09-29 | 1983-09-29 | Quantizing method of multi-value picture information |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP58182134A JPS6074772A (en) | 1983-09-29 | 1983-09-29 | Quantizing method of multi-value picture information |
Publications (2)
Publication Number | Publication Date |
---|---|
JPS6074772A JPS6074772A (en) | 1985-04-27 |
JPH0126591B2 true JPH0126591B2 (en) | 1989-05-24 |
Family
ID=16112926
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
JP58182134A Granted JPS6074772A (en) | 1983-09-29 | 1983-09-29 | Quantizing method of multi-value picture information |
Country Status (1)
Country | Link |
---|---|
JP (1) | JPS6074772A (en) |
Families Citing this family (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPH06103922B2 (en) * | 1987-07-24 | 1994-12-14 | 松下電器産業株式会社 | Image signal processor |
Citations (8)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPS5230319A (en) * | 1975-09-04 | 1977-03-08 | Nippon Hoso Kyokai <Nhk> | Compensation circuit of digital type gamma |
JPS5387621A (en) * | 1977-01-12 | 1978-08-02 | Matsushita Electric Ind Co Ltd | Outline emphasizing circuit |
JPS54116120A (en) * | 1978-03-02 | 1979-09-10 | Toshiba Corp | Quantizing method of video signal and its unit |
JPS54128214A (en) * | 1978-03-29 | 1979-10-04 | Ricoh Co Ltd | Sampling quantizing device for picture |
JPS54144139A (en) * | 1978-05-01 | 1979-11-10 | Ricoh Co Ltd | Processing system for intermediate tone |
JPS561667A (en) * | 1979-06-19 | 1981-01-09 | Ricoh Co Ltd | Gamma correcting system for picture input/output device |
JPS57125579A (en) * | 1981-01-29 | 1982-08-04 | Ricoh Co Ltd | Processing method for intermediate tone picture |
JPS5896459A (en) * | 1981-12-04 | 1983-06-08 | Matsushita Electric Ind Co Ltd | Quantizing method for picture luminance signal |
-
1983
- 1983-09-29 JP JP58182134A patent/JPS6074772A/en active Granted
Patent Citations (8)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPS5230319A (en) * | 1975-09-04 | 1977-03-08 | Nippon Hoso Kyokai <Nhk> | Compensation circuit of digital type gamma |
JPS5387621A (en) * | 1977-01-12 | 1978-08-02 | Matsushita Electric Ind Co Ltd | Outline emphasizing circuit |
JPS54116120A (en) * | 1978-03-02 | 1979-09-10 | Toshiba Corp | Quantizing method of video signal and its unit |
JPS54128214A (en) * | 1978-03-29 | 1979-10-04 | Ricoh Co Ltd | Sampling quantizing device for picture |
JPS54144139A (en) * | 1978-05-01 | 1979-11-10 | Ricoh Co Ltd | Processing system for intermediate tone |
JPS561667A (en) * | 1979-06-19 | 1981-01-09 | Ricoh Co Ltd | Gamma correcting system for picture input/output device |
JPS57125579A (en) * | 1981-01-29 | 1982-08-04 | Ricoh Co Ltd | Processing method for intermediate tone picture |
JPS5896459A (en) * | 1981-12-04 | 1983-06-08 | Matsushita Electric Ind Co Ltd | Quantizing method for picture luminance signal |
Also Published As
Publication number | Publication date |
---|---|
JPS6074772A (en) | 1985-04-27 |
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