JP2011022868A - Image processing device and method thereof - Google Patents
Image processing device and method thereof Download PDFInfo
- Publication number
- JP2011022868A JP2011022868A JP2009168275A JP2009168275A JP2011022868A JP 2011022868 A JP2011022868 A JP 2011022868A JP 2009168275 A JP2009168275 A JP 2009168275A JP 2009168275 A JP2009168275 A JP 2009168275A JP 2011022868 A JP2011022868 A JP 2011022868A
- Authority
- JP
- Japan
- Prior art keywords
- restoration
- image
- transfer function
- frequency
- image output
- 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.)
- Granted
Links
- 238000012545 processing Methods 0.000 title claims abstract description 43
- 238000000034 method Methods 0.000 title claims description 25
- 238000012546 transfer Methods 0.000 claims abstract description 34
- 230000006866 deterioration Effects 0.000 claims abstract description 9
- 230000008569 process Effects 0.000 claims description 24
- 230000000007 visual effect Effects 0.000 claims description 12
- 238000001514 detection method Methods 0.000 claims description 7
- 238000004458 analytical method Methods 0.000 claims description 6
- 238000004364 calculation method Methods 0.000 claims description 5
- 230000015556 catabolic process Effects 0.000 claims description 5
- 238000006731 degradation reaction Methods 0.000 claims description 5
- 238000003672 processing method Methods 0.000 claims 2
- 230000008859 change Effects 0.000 description 13
- 238000005259 measurement Methods 0.000 description 11
- 238000003860 storage Methods 0.000 description 8
- 230000007423 decrease Effects 0.000 description 4
- 238000010586 diagram Methods 0.000 description 4
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 230000009467 reduction Effects 0.000 description 2
- 241000282412 Homo Species 0.000 description 1
- 238000013459 approach Methods 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 238000001914 filtration Methods 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 238000000691 measurement method Methods 0.000 description 1
- 230000035945 sensitivity Effects 0.000 description 1
- 238000001228 spectrum Methods 0.000 description 1
Landscapes
- Image Processing (AREA)
- Facsimile Image Signal Circuits (AREA)
Abstract
Description
本発明は、画像出力機器に起因する画質劣化を復元する画像処理に関する。 The present invention relates to image processing for restoring image quality degradation caused by an image output device.
画像の入出力機器を用いて画像データを入出力する際に、入出力機器による画像の先鋭性の低下、暈けなど画像データの周波数特性の劣化を補正する処理（以下、復元処理）がある。復元処理は、一般に、フーリエ変換などを用いて周波数空間のデータに変換した画像データに復元フィルタによるフィルタリングを施す。例えば特許文献1は、ノイズの影響を考慮したWienerフィルタを用いて復元処理を行う。また、特許文献2は、フィルタにより復元処理を行う際、ユーザが復元の度合いを調整できるように調整パラメータを導入する。 When inputting / outputting image data using an image input / output device, there is a process for correcting deterioration of the frequency characteristics of the image data, such as a decrease in sharpness or blurring of the image by the input / output device (hereinafter referred to as restoration process) . In the restoration process, generally, image data converted into frequency space data using Fourier transform or the like is subjected to filtering by a restoration filter. For example, Patent Document 1 performs restoration processing using a Wiener filter that takes into account the influence of noise. Patent Document 2 introduces an adjustment parameter so that the user can adjust the degree of restoration when performing restoration processing using a filter.
しかし、入出力機器には復元処理の限界（以下、復元限界）がある場合がある。図1により画像をプリンタで印刷する場合の復元限界を説明する。図1(a)に示す輝度変化を有する画像を印刷した場合、プリンタの空間周波数伝達関数(modulation transfer function: MTF)特性により、図1(b)に示すようにコントラストが低下する。 However, there is a case where the input / output device has a limit of restoration processing (hereinafter, restoration limit). The restoration limit when an image is printed by a printer will be described with reference to FIG. When an image having a luminance change shown in FIG. 1 (a) is printed, the contrast is lowered as shown in FIG. 1 (b) due to the spatial transfer function (MTF) characteristic of the printer.
そこで、MTFの逆関数である復元フィルタ（逆フィルタ）を用いた復元処理を行い、プリンタに供給する画像データの輝度変化を図1(c)に示す変化に補正する。しかし、8ビット画像処理の場合、値0〜255の範囲に画像データを丸め込む必要があり、範囲外のデータをクリップする。その結果、プリンタに出力する画像データの輝度変化は、図1(c)に破線で示す部分がクリップされた、実線で示す変化になる。そして、印刷時、プリンタのMTF特性による劣化が生じ、出力画像の輝度変化は図1(d)に示すようになる。つまり、図1(b)に比べてコントラストは改善されるものの、階調変化に劣化が生じる。 Therefore, restoration processing using a restoration filter (inverse filter) that is an inverse function of MTF is performed, and the luminance change of the image data supplied to the printer is corrected to the change shown in FIG. However, in the case of 8-bit image processing, it is necessary to round the image data to a range of values 0 to 255, and data outside the range is clipped. As a result, the luminance change of the image data output to the printer is a change indicated by a solid line in which the portion indicated by the broken line in FIG. During printing, deterioration due to the MTF characteristics of the printer occurs, and the luminance change of the output image is as shown in FIG. That is, although the contrast is improved as compared with FIG. 1B, the gradation change is degraded.
そこで、図1(e)に示すように、クリップが発生しない最大のコントラストを考慮して復元処理を行えば、図1(f)に示すようにコントラスト、階調変化ともに良好な出力画像を得ることができる。つまり、この最大のコントラストが復元限界の一例である。 Therefore, as shown in FIG. 1 (e), if restoration processing is performed in consideration of the maximum contrast at which clipping does not occur, an output image with good contrast and gradation changes can be obtained as shown in FIG. 1 (f). be able to. That is, this maximum contrast is an example of the restoration limit.
本発明は、復元限界を考慮して、画像出力装置に起因する画質劣化を抑制することを目的とする。 An object of the present invention is to suppress image quality deterioration caused by an image output device in consideration of a restoration limit.
本発明は、前記の目的を達成する一手段として、以下の構成を備える。 The present invention has the following configuration as one means for achieving the above object.
本発明にかかる画像処理は、画像出力装置に出力する画像の周波数特性を解析し、前記画像出力装置の空間周波数伝達関数に基づく復元フィルタ、および、前記周波数特性に基づく復元フィルタを作成し、前記空間周波数伝達関数と前記周波数特性を比較して復元限界を検出し、前記復元限界に基づき前記復元フィルタの何れかを用いて、前記画像出力装置に起因する画質劣化を復元する復元処理を前記画像に施すことを特徴とする。 The image processing according to the present invention analyzes a frequency characteristic of an image output to an image output device, creates a restoration filter based on a spatial frequency transfer function of the image output device, and a restoration filter based on the frequency characteristic, A restoration limit is detected by comparing a spatial frequency transfer function and the frequency characteristic, and restoration processing for restoring image quality degradation caused by the image output device is performed using any of the restoration filters based on the restoration limit. It is characterized by applying to.
また、画像の出力先の画像出力装置の空間周波数伝達関数に基づく復元フィルタ、および、視覚伝達関数に基づく復元フィルタを作成し、周波数ごとに、前記空間周波数伝達関数と前記視覚伝達関数を比較して、復元限界として前記空間周波数伝達関数または前記視覚伝達関数を設定し、前記復元限界に基づき前記復元フィルタの何れかを用いて、前記画像出力装置に起因する画質劣化を復元する復元処理を前記画像に施すことを特徴とする。 Also, a restoration filter based on the spatial frequency transfer function and a restoration filter based on the visual transfer function of the image output device of the image output destination are created, and the spatial frequency transfer function and the visual transfer function are compared for each frequency. Setting the spatial frequency transfer function or the visual transfer function as a restoration limit, and using any one of the restoration filters based on the restoration limit, the restoration process for restoring the image quality degradation caused by the image output device It is applied to an image.
本発明によれば、復元限界を考慮して、画像出力装置に起因する画質劣化を抑制することができる。 According to the present invention, it is possible to suppress deterioration in image quality caused by the image output device in consideration of the restoration limit.
以下、本発明にかかる実施例の画像処理を図面を参照して詳細に説明する。 Hereinafter, image processing according to an embodiment of the present invention will be described in detail with reference to the drawings.
［装置の構成］
図2のブロック図により実施例1の画像処理装置100の構成例を説明する。
[Device configuration]
A configuration example of the image processing apparatus 100 according to the first embodiment will be described with reference to the block diagram of FIG.
画像出力装置102は、インクジェットプリンタや電子写真プリンタなど、入力された画像データが表す画像を印刷するプリンタである。測定装置103は、スキャナやディジタルカメラなど、画像出力装置102が出力したチャートの濃度分布を測定する装置である。画像記憶部106は、画像出力装置102によって印刷する画像データなど様々な画像を記憶する記憶装置である。なお、ネットワークに接続されたサーバ装置などを記憶装置の代わりに利用してもよい。 The image output device 102 is a printer that prints an image represented by input image data, such as an inkjet printer or an electrophotographic printer. The measurement device 103 is a device that measures the density distribution of the chart output from the image output device 102, such as a scanner or a digital camera. The image storage unit 106 is a storage device that stores various images such as image data to be printed by the image output device 102. A server device or the like connected to the network may be used instead of the storage device.
画像処理装置100において、MTF特性算出部14は、測定装置103から入力したチャートの測定データを基に画像出力装置102の空間周波数伝達関数(modulation transfer function: MTF)特性を算出する。画像入力部17は、画像記憶部106が記憶する画像データを読み込む。周波数特性解析部18は、画像入力部17が読み込んだ画像データをフーリエ変換して、画像データの周波数特性を解析する。復元フィルタ作成部15は、画像出力装置102のMTF特性および画像データの周波数特性に基づき復元フィルタを作成する。 In the image processing apparatus 100, the MTF characteristic calculation unit 14 calculates the spatial frequency transfer function (MTF) characteristic of the image output apparatus 102 based on the measurement data of the chart input from the measurement apparatus 103. The image input unit 17 reads image data stored in the image storage unit 106. The frequency characteristic analysis unit 18 performs Fourier transform on the image data read by the image input unit 17 and analyzes the frequency characteristic of the image data. The restoration filter creation unit 15 creates a restoration filter based on the MTF characteristics of the image output device 102 and the frequency characteristics of the image data.
復元限界検出部19は、画像出力装置102のMTF特性および画像データの周波数特性を基に、画像出力装置102の復元限界を検出する。復元フィルタ設定部20は、復元限界検出部19が検出した画像出力装置102の復元限界に基づき、復元処理に適用する復元フィルタを設定する。 The restoration limit detection unit 19 detects the restoration limit of the image output device 102 based on the MTF characteristics of the image output device 102 and the frequency characteristics of the image data. The restoration filter setting unit 20 sets a restoration filter to be applied to the restoration process based on the restoration limit of the image output device 102 detected by the restoration limit detection unit 19.
復元部21は、周波数特性解析部18のフーリエ変換によって得られた周波数空間の画像データに、復元フィルタ設定部20が設定した復元フィルタを使用する復元処理を施す。逆変換部22は、逆フーリエ変換により、復元処理された周波数空間の画像データを実空間の画像データに逆変換する。画像出力部23は、復元処理され、実空間に逆変換された画像データを、その出力先である画像出力装置102に出力する。 The restoration unit 21 performs a restoration process using the restoration filter set by the restoration filter setting unit 20 on the image data in the frequency space obtained by the Fourier transform of the frequency characteristic analysis unit 18. The inverse transform unit 22 inversely transforms the restored frequency space image data into real space image data by inverse Fourier transform. The image output unit 23 outputs the image data that has been subjected to the restoration process and converted back to the real space to the image output device 102 that is the output destination.
［復元処理］
図3のフローチャートにより画像処理装置100の復元処理を説明する。
[Restore processing]
The restoration process of the image processing apparatus 100 will be described with reference to the flowchart of FIG.
MTF特性算出部14は、詳細は後述するが、画像出力装置102が印刷したMTF測定用のチャートの測定結果を測定装置103から入力して画像出力装置102のMTF特性を算出する(S201)。復元フィルタ作成部15は、画像出力装置102のMTF特性の逆関数および原画像の周波数特性の逆関数を算出し、復元フィルタを作成する(S202)。 The MTF characteristic calculation unit 14 calculates the MTF characteristic of the image output apparatus 102 by inputting the measurement result of the MTF measurement chart printed by the image output apparatus 102 from the measurement apparatus 103, as will be described in detail later (S201). The restoration filter creation unit 15 calculates an inverse function of the MTF characteristic of the image output device 102 and an inverse function of the frequency characteristic of the original image, and creates a restoration filter (S202).
次に、画像入力部17は、画像記憶部106に記憶された印刷すべき画像（以下、原画像）の画像データを読み込む(S203)。周波数特性解析部18は、原画像の画像データをフーリエ変換して、原画像の周波数特性を解析する(S204)。復元限界検出部19は、詳細は後述するが、画像出力装置102のMTF特性および原画像の周波数特性を基に、画像出力装置102の復元限界を検出する(S205)。 Next, the image input unit 17 reads image data of an image to be printed (hereinafter referred to as an original image) stored in the image storage unit 106 (S203). The frequency characteristic analysis unit 18 performs Fourier transform on the image data of the original image and analyzes the frequency characteristic of the original image (S204). Although details will be described later, the restoration limit detection unit 19 detects the restoration limit of the image output apparatus 102 based on the MTF characteristics of the image output apparatus 102 and the frequency characteristics of the original image (S205).
次に、復元フィルタ設定部20は、詳細は後述するが、復元限界検出部19が検出した画像出力装置102の復元限界に基づき、復元処理に適用する復元フィルタを設定する(S206)。復元部21は、周波数特性解析部18のフーリエ変換によって得られた、原画像の周波数空間の画像データに、設定された復元フィルタを用いる復元処理を施す(S207)。 Next, as will be described in detail later, the restoration filter setting unit 20 sets a restoration filter to be applied to the restoration process based on the restoration limit of the image output device 102 detected by the restoration limit detection unit 19 (S206). The restoration unit 21 performs restoration processing using the set restoration filter on the image data in the frequency space of the original image obtained by the Fourier transform of the frequency characteristic analysis unit 18 (S207).
次に、逆変換部22は、復元処理された周波数空間の画像データ（以下、復元画像の画像データ）を逆フーリエ変換する(S208)。画像出力部23は、復元画像の画像データを画像出力装置102に出力し(S209)、画像出力装置102に復元画像を印刷させる。 Next, the inverse transform unit 22 performs inverse Fourier transform on the restored frequency space image data (hereinafter, image data of the restored image) (S208). The image output unit 23 outputs the image data of the restored image to the image output device 102 (S209), and causes the image output device 102 to print the restored image.
［MTF特性算出部］
一般に、画像出力機器によって画像を出力する場合、画像出力機器の特性により、コントラストが低下し、コントラストの低下の度合いは入力する画像の周波数特性に依存する。図4によりコントラスト低下の周波数特性の依存性を説明する。
[MTF characteristic calculator]
In general, when an image is output by an image output device, the contrast decreases due to the characteristics of the image output device, and the degree of the decrease in contrast depends on the frequency characteristics of the input image. With reference to FIG. 4, the dependence of the frequency characteristics of the contrast reduction will be described.
図4(a)、図4(c)、図4(e)は振幅が同一で周波数が異なる正弦波状の輝度変化を示している。このような輝度変化を示す画像データを画像出力機器に入力すると、それぞれ図4(b)、図4(d)、図4(f)に示す出力結果が得られる。つまり、同一の振幅（同一のコントラスト）をもつ正弦波状の輝度変化でも、その周波数により、出力画像におけるコントラストの低下の度合いが異なる。 4 (a), 4 (c), and 4 (e) show sinusoidal luminance changes with the same amplitude but different frequencies. When image data indicating such a luminance change is input to an image output device, output results shown in FIGS. 4B, 4D, and 4F are obtained, respectively. That is, even in a sinusoidal luminance change having the same amplitude (same contrast), the degree of contrast reduction in the output image differs depending on the frequency.
そこで、横軸を解像度（周波数）、縦軸をコントラスト比として、入力データのコントラストと出力画像のコントラストの比をプロットすると図5に示すようなMTF特性が得られる。 Therefore, when the ratio of the contrast of the input data and the contrast of the output image is plotted with the horizontal axis representing the resolution (frequency) and the vertical axis representing the contrast ratio, an MTF characteristic as shown in FIG. 5 is obtained.
図6、図7によりMTF測定用チャートの一例を説明する。MTFを測定する際は、図6に示すような、正弦波状の輝度変化をもち、輝度変化の周波数を変化させた測定用のチャートを画像出力装置102に印刷させ、測定装置103によってチャートの画像データを取得する。MTF特性算出部14は、輝度変化の各周波数について、入力データのコントラストと、チャートの画像データのコントラストからコントラスト比を算出して、画像出力装置102のMTF特性を得る。 An example of the MTF measurement chart will be described with reference to FIGS. When measuring the MTF, a chart for measurement having a sinusoidal luminance change as shown in FIG. 6 and changing the frequency of the luminance change is printed on the image output device 102, and the image of the chart is measured by the measuring device 103. Get the data. The MTF characteristic calculation unit 14 calculates the contrast ratio from the contrast of the input data and the contrast of the image data of the chart for each frequency of the luminance change, and obtains the MTF characteristic of the image output device 102.
図6は横方向に輝度が変化するチャート例であるが、さらに、図7に示すような縦方向に輝度が変化するチャートを用いれば横方向と縦方向のMTF特性が得られ、斜め方向を補間して二次元のMTF特性を算出することができる。 FIG. 6 shows an example of a chart in which the luminance changes in the horizontal direction. Further, if a chart in which the luminance changes in the vertical direction as shown in FIG. A two-dimensional MTF characteristic can be calculated by interpolation.
また、画像出力機器のMTF特性が、周波数および二次元的な方向だけでなく、画像の出力位置や画像の明るさや画像データの振幅などに依存する場合は、それらに対応する測定用チャートを用意する。例えば、周波数が同一で振幅が異なる正弦波状の輝度変化を示すチャートを印刷し、画像データの特性に対応するMTF特性を選定し、復元フィルタを作成すればよい。言い替えれば、ユーザが所望する画像出力機器のMTF特性を算出することが可能であれば、その測定方法や算出方法は限定されない。 If the MTF characteristics of the image output device depend not only on the frequency and two-dimensional direction, but also on the output position of the image, the brightness of the image, the amplitude of the image data, etc., a corresponding measurement chart is prepared. To do. For example, a chart showing sinusoidal luminance changes with the same frequency and different amplitudes may be printed, an MTF characteristic corresponding to the characteristic of the image data may be selected, and a restoration filter may be created. In other words, as long as it is possible to calculate the MTF characteristics of the image output device desired by the user, the measurement method and calculation method are not limited.
［復元フィルタの制御と設定］
図8により画像の周波数特性が画像出力機器のMTF特性により劣化する例を説明する。図8(a)は原画像の周波数特性例を示し、図8(b)は画像出力機器のMTF特性例を示す。出力画像の周波数特性は、図8(a)の特性と図8(b)の特性を掛け合わせた、図8(c)に実線で示す特性になる。
Restore filter control and settings
An example in which the frequency characteristics of an image deteriorate due to the MTF characteristics of the image output device will be described with reference to FIG. FIG. 8 (a) shows an example of frequency characteristics of the original image, and FIG. 8 (b) shows an example of MTF characteristics of the image output device. The frequency characteristic of the output image is a characteristic indicated by a solid line in FIG. 8C, which is obtained by multiplying the characteristic of FIG. 8A by the characteristic of FIG. 8B.
図9により復元フィルタを説明する。理想的には、図9(a)に示すような、画像出力機器のMTF特性（図8(b)）の逆関数（つまり逆フィルタ）作成する。そして、逆関数を原画像の周波数特性（図8(a)）に掛けることで、画像出力機器のMTF特性をキャンセルして、原画像と出力画像の周波数特性を一致させることができる。 The restoration filter will be described with reference to FIG. Ideally, an inverse function (that is, an inverse filter) of the MTF characteristic (FIG. 8 (b)) of the image output device is created as shown in FIG. 9 (a). Then, by applying the inverse function to the frequency characteristics (FIG. 8 (a)) of the original image, the MTF characteristics of the image output device can be canceled and the frequency characteristics of the original image and the output image can be matched.
しかし、図9(a)に示すように、MTF特性が零に近付く高周波数域において逆フィルタの絶対値は急激に増大する。このような逆フィルタで原画像の復元処理すれば、復元画像の画素の中には画像出力機器のデータ範囲（例えば8ビット画像の場合は0〜255）を逸脱するものが発生する。その結果、画素値を画像出力機器のデータ範囲に丸める処理（クリップ）が必要になり、期待どおりの周波数特性を有する出力画像が得られない。 However, as shown in FIG. 9 (a), the absolute value of the inverse filter increases rapidly in a high frequency region where the MTF characteristic approaches zero. When the original image is restored using such an inverse filter, some pixels of the restored image deviate from the data range of the image output device (for example, 0 to 255 in the case of an 8-bit image). As a result, a process (clip) for rounding the pixel value to the data range of the image output device is required, and an output image having an expected frequency characteristic cannot be obtained.
そこで、画像出力機器が出力し得る最大コントラストを示すMTF特性を利用する。つまり、原画像のパワーが画像出力機器のMTF特性を超えない周波数域は原画像のパワーを復元の目標値にする。逆に、原画像のパワーが画像出力機器のMTF特性を超える周波数域はMTF特性の値を復元の目標値にする。 Therefore, the MTF characteristic indicating the maximum contrast that can be output by the image output device is used. That is, in the frequency range where the power of the original image does not exceed the MTF characteristics of the image output device, the power of the original image is set as a restoration target value. Conversely, in the frequency range where the power of the original image exceeds the MTF characteristic of the image output device, the value of the MTF characteristic is set as a target value for restoration.
つまり、復元限界検出部19は、原画像のパワーが画像出力装置102のMTF特性を超える周波数νsを画像出力装置102の復元限界として検出する。そして、復元フィルタ設定部20は、周波数が復元限界以下の周波数成分の回復処理にMTF特性G(ν)の逆フィルタを適用し、周波数が復元限界を超える周波数成分の回復処理に原画像のパワーF(ν)の逆フィルタを適用する。つまり、復元フィルタは下式によって表される。
if (ν ≦ νs)
H(ν) = 1/G(ν);
else
H(ν) = 1/F(ν); …(1)
ここで、F(ν)は原画像のパワースペクトル、
G(ν)は画像出力機器のMTF特性、
νは空間周波数(cycles/degree)。
That is, the restoration limit detection unit 19 detects the frequency νs at which the power of the original image exceeds the MTF characteristic of the image output device 102 as the restoration limit of the image output device 102. Then, the restoration filter setting unit 20 applies the inverse filter of the MTF characteristic G (ν) to the restoration processing of the frequency component whose frequency is below the restoration limit, and the power of the original image to the restoration processing of the frequency component whose frequency exceeds the restoration limit Apply an inverse filter of F (ν). That is, the restoration filter is expressed by the following equation.
if (ν ≦ νs)
H (ν) = 1 / G (ν);
else
H (ν) = 1 / F (ν);… (1)
Where F (ν) is the power spectrum of the original image,
G (ν) is the MTF characteristic of the image output device,
ν is the spatial frequency (cycles / degree).
図9(b)は式(1)の復元フィルタの周波数特性を示し、この復元フィルタを原画像に掛けた復元画像を画像出力機器によって出力すれば、図9(c)に示す周波数特性の出力画像が得られる。つまり、画像出力機器によって出力し得る最良の周波数特性を有する出力画像を得ることができる。 FIG. 9 (b) shows the frequency characteristics of the restoration filter of Equation (1), and if the restored image obtained by applying this restoration filter to the original image is output by the image output device, the output of the frequency characteristics shown in FIG. 9 (c) An image is obtained. That is, an output image having the best frequency characteristic that can be output by the image output device can be obtained.
［変形例］
実空間フィルタのコンボリューションによって復元処理を行う場合は、原画像の各画素について、復元限界の検出および復元フィルタの設定を行う。これにより、画素ごとに異なる復元限界の違いに対応することができる。
[Modification]
When the restoration process is performed by convolution of the real space filter, the restoration limit is detected and the restoration filter is set for each pixel of the original image. Thereby, it is possible to cope with a difference in restoration limit that is different for each pixel.
また、上記では、一台の画像出力装置102を対象に説明したが、複数の画像出力装置をタンデム運転する場合は、それら画像出力装置の固体差（製造誤差）を考慮する。つまり、最も特性が悪い装置のMTF特性を測定または推定して、何れの装置においても復元限界を超えないように復元フィルタを作成し、復元限界を検出する。 In the above description, a single image output device 102 has been described. However, when a plurality of image output devices are operated in tandem, individual differences (manufacturing errors) of these image output devices are taken into consideration. That is, the MTF characteristic of the device having the worst characteristics is measured or estimated, a restoration filter is created so as not to exceed the restoration limit in any apparatus, and the restoration limit is detected.
以下、本発明にかかる実施例2の画像処理を説明する。なお、実施例2において、実施例1と略同様の構成については、同一符号を付して、その詳細説明を省略する。 The image processing according to the second embodiment of the present invention will be described below. Note that the same reference numerals in the second embodiment denote the same parts as in the first embodiment, and a detailed description thereof will be omitted.
図10のブロック図により実施例2の画像処理装置100の構成例を説明する。実施例2の画像処理装置100は、実施例1の周波数特性解析部18の代わりに、原画像の画像データをフーリエ変換するだけのフーリエ変換部25を備える。また、復元限界検出部19の代わりに、復元限界設定部26を備える。さらに、人間の視覚伝達関数(visual transfer function: VTF)特性を記憶するVTF特性記憶部24を備え、復元フィルタ作成部15は、画像出力装置102のMTF特性およびVTF特性に基づき復元フィルタを作成する。その他の構成は、実施例1の画像処理装置100と同様である。 A configuration example of the image processing apparatus 100 according to the second embodiment will be described with reference to the block diagram of FIG. The image processing apparatus 100 according to the second embodiment includes a Fourier transform unit 25 that only performs Fourier transform on the image data of the original image, instead of the frequency characteristic analysis unit 18 according to the first embodiment. In addition, a restoration limit setting unit 26 is provided instead of the restoration limit detection unit 19. Furthermore, a VTF characteristic storage unit 24 that stores human visual transfer function (VTF) characteristics is provided, and the restoration filter creation unit 15 creates a restoration filter based on the MTF characteristics and VTF characteristics of the image output device 102. . Other configurations are the same as those of the image processing apparatus 100 of the first embodiment.
図11のフローチャートにより実施例2の画像処理装置100の復元処理を説明する。実施例2においては、フーリエ変換部25が原画像の画像データをフーリエ変換し(S304)、復元限界設定部26が画像出力装置102のMTF特性およびVTF特性を基に復元フィルタを制御する(S305)点で、実施例1の復元処理と異なる。なお、ステップS202において、復元フィルタ作成部15が復元フィルタを作成する点は変わらないが、復元フィルタの逆関数が画像出力装置102のMTF特性とVTF特性である点で異なる。その他の処理は、実施例1と同様である。 The restoration process of the image processing apparatus 100 according to the second embodiment will be described with reference to the flowchart of FIG. In the second embodiment, the Fourier transform unit 25 performs Fourier transform on the image data of the original image (S304), and the restoration limit setting unit 26 controls the restoration filter based on the MTF characteristic and the VTF characteristic of the image output device 102 (S305). This is different from the restoration process of the first embodiment. In step S202, the point that the restoration filter creation unit 15 creates the restoration filter does not change, but the difference is that the inverse function of the restoration filter is the MTF characteristic and the VTF characteristic of the image output device 102. Other processes are the same as those in the first embodiment.
図12のフローチャートにより復元限界設定部26の処理を詳細に説明する。 The processing of the restoration limit setting unit 26 will be described in detail with reference to the flowchart of FIG.
復元限界設定部26は、画像出力装置102のMTF特性を読み込み(S401)、VTF特性記憶部24が記憶するVTF特性を読み込み(S402)、注目周波数を直流成分（周波数ν=0）に設定する(S403)。 The restoration limit setting unit 26 reads the MTF characteristic of the image output device 102 (S401), reads the VTF characteristic stored in the VTF characteristic storage unit 24 (S402), and sets the frequency of interest to a DC component (frequency ν = 0). (S403).
次に、復元限界設定部26は、注目周波数のMTF特性とVTF特性を比較し(S404)、値が小さい特性を当該周波数の復元限界に設定する(S405)。そして、復元限界を設定する全周波数について、復元限界を設定したか否かを判定し(S406)、未設定の周波数があれば、注目周波数を高周波数側に移動し(S407)、処理をステップS404に戻す。 Next, the restoration limit setting unit 26 compares the MTF characteristic and VTF characteristic of the frequency of interest (S404), and sets a characteristic having a small value as the restoration limit of the frequency (S405). Then, it is determined whether or not the restoration limit has been set for all frequencies for which the restoration limit is set (S406). Return to S404.
このようにして、復元限界設定部26は、フーリエ変換部25が出力する周波数成分に対応する周波数の復元限界をMTF特性またはVTF特性に設定する。復元フィルタ設定部20は、復元限界設定部26が設定した復元限界に応じて復元処理に適用する復元フィルタを設定する。つまり、復元限界がMTF特性G(ν)の周波数に対応する周波数成分の復元処理に復元フィルタH(ν)=1/G(ν)を設定し、復元限界がVTF特性V(ν)の周波数に対応する周波数成分の復元処理に復元フィルタH(ν)=1/V(ν)を設定する。従って、復元部21は、復元限界設定部26が周波数ごとに設定した復元限界に応じた復元フィルタを用いる復元処理を各周波数成分に施すことになる。 In this way, the restoration limit setting unit 26 sets the frequency restoration limit corresponding to the frequency component output by the Fourier transform unit 25 to the MTF characteristic or the VTF characteristic. The restoration filter setting unit 20 sets a restoration filter to be applied to the restoration process according to the restoration limit set by the restoration limit setting unit 26. In other words, the restoration filter H (ν) = 1 / G (ν) is set for the restoration processing of the frequency component corresponding to the frequency of the MTF characteristic G (ν) whose restoration limit is the frequency, and the restoration limit is the frequency of the VTF characteristic V (ν). A restoration filter H (ν) = 1 / V (ν) is set in the restoration processing of the frequency component corresponding to. Therefore, the restoration unit 21 performs the restoration process using the restoration filter corresponding to the restoration limit set for each frequency by the restoration limit setting unit 26 on each frequency component.
［復元限界の設定］
復元限界の設定の詳細を説明する。人間の視覚の伝達関数であるVTF特性は下式によって近似することができる。
if (ν≧ 5)
VTF = 5.05e-0.138ν(1 - e-0.1ν);
else
VTF = 1; …(2)
[Restore limit setting]
Details of setting the restoration limit will be described. The VTF characteristic, which is the transfer function of human vision, can be approximated by the following equation.
if (ν ≧ 5)
VTF = 5.05e -0.138ν (1-e -0.1ν );
else
VTF = 1;… (2)
式(2)によって得られるVTFの値をプロットすると図13に示す特性になる。図13に示すように、周波数が高くなるに連れ、視覚感度が低下する。つまり、人間は、VTF特性よりも小さいコントラストを知覚することができない。つまり、VTF特性に合わせて復元処理を行えば、画質劣化が改善されたと知覚される。そこで、復元限界の決定において、画像出力装置102のMTF特性とVTF特性を比較し、値が小さい方を復元限界に設定する。 Plotting the value of VTF obtained by equation (2) gives the characteristics shown in FIG. As shown in FIG. 13, the visual sensitivity decreases as the frequency increases. That is, humans cannot perceive a contrast smaller than the VTF characteristic. In other words, it is perceived that the image quality deterioration has been improved by performing the restoration process according to the VTF characteristics. Therefore, in determining the restoration limit, the MTF characteristic and the VTF characteristic of the image output apparatus 102 are compared, and the smaller value is set as the restoration limit.
［変形例］
実施例2では、画像出力機器における復元処理を説明したが、画像入力機器においても同様の復元処理が可能である。つまり、画像入力機器のMTF特性を算出し、MTF特性とVTF特性から復元フィルタを作成する。そして、MTF特性とVTF特性を比較して復元限界を何れかに設定し、設定した復元限界に応じた復元フィルタを用いる復元処理を画像入力機器から入力した原画像の周波数成分に施す。そして、復元画像を逆フーリエ変換すれば、画像入力機器に起因する画像劣化を抑制することができる。
[Modification]
In the second embodiment, the restoration process in the image output device has been described. However, the same restoration process can be performed in the image input device. That is, the MTF characteristic of the image input device is calculated, and a restoration filter is created from the MTF characteristic and the VTF characteristic. Then, the restoration limit is set to any one by comparing the MTF characteristic and the VTF characteristic, and the restoration process using the restoration filter corresponding to the set restoration limit is performed on the frequency component of the original image input from the image input device. Then, if the restored image is subjected to inverse Fourier transform, image deterioration caused by the image input device can be suppressed.
［その他の実施例］
また、本発明は、以下の処理を実行することによっても実現される。即ち、上述した実施形態の機能を実現するソフトウェア（プログラム）を、ネットワーク又は各種記憶媒体を介してシステム或いは装置に供給し、そのシステムあるいは装置のコンピュータ（又はCPUやMPU等）がプログラムを読み出して実行する処理である。
[Other Examples]
The present invention can also be realized by executing the following processing. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and a computer (or CPU, MPU, etc.) of the system or apparatus reads the program. It is a process to be executed.
Claims (9)
前記画像出力装置の空間周波数伝達関数に基づく復元フィルタ、および、前記周波数特性に基づく復元フィルタを作成する作成手段と、
前記空間周波数伝達関数と前記周波数特性を比較して復元限界を検出する検出手段と、
前記復元限界に基づき前記復元フィルタの何れかを用いて、前記画像出力装置に起因する画質劣化を復元する復元処理を前記画像に施す復元手段とを有することを特徴とする画像処理装置。 Analysis means for analyzing the frequency characteristics of the image output to the image output device;
A restoration filter based on a spatial frequency transfer function of the image output device, and a creation means for creating a restoration filter based on the frequency characteristics;
Detecting means for comparing the spatial frequency transfer function and the frequency characteristic to detect a restoration limit;
An image processing apparatus comprising: a restoration unit configured to perform restoration processing for restoring image quality deterioration caused by the image output device using any one of the restoration filters based on the restoration limit.
周波数ごとに、前記空間周波数伝達関数と前記視覚伝達関数を比較して、復元限界として前記空間周波数伝達関数または前記視覚伝達関数を設定する設定手段と、
前記復元限界に基づき前記復元フィルタの何れかを用いて、前記画像出力装置に起因する画質劣化を復元する復元処理を前記画像に施す復元手段とを有することを特徴とする画像処理装置。 A creation filter for creating a restoration filter based on a spatial frequency transfer function of an image output device of an image output destination, and a restoration filter based on a visual transfer function;
Setting means for comparing the spatial frequency transfer function and the visual transfer function for each frequency, and setting the spatial frequency transfer function or the visual transfer function as a restoration limit;
An image processing apparatus comprising: a restoration unit configured to perform restoration processing for restoring image quality deterioration caused by the image output device using any one of the restoration filters based on the restoration limit.
前記画像出力装置の空間周波数伝達関数に基づく復元フィルタ、および、前記周波数特性に基づく復元フィルタを作成し、
前記空間周波数伝達関数と前記周波数特性を比較して復元限界を検出し、
前記復元限界に基づき前記復元フィルタの何れかを用いて、前記画像出力装置に起因する画質劣化を復元する復元処理を前記画像に施すことを特徴とする画像処理方法。 Analyzing the frequency characteristics of the image output to the image output device,
Creating a restoration filter based on a spatial frequency transfer function of the image output device, and a restoration filter based on the frequency characteristic;
Comparing the spatial frequency transfer function and the frequency characteristic to detect a restoration limit;
An image processing method, wherein a restoration process for restoring image quality degradation caused by the image output device is performed on the image using any one of the restoration filters based on the restoration limit.
周波数ごとに、前記空間周波数伝達関数と前記視覚伝達関数を比較して、復元限界として前記空間周波数伝達関数または前記視覚伝達関数を設定し、
前記復元限界に基づき前記復元フィルタの何れかを用いて、前記画像出力装置に起因する画質劣化を復元する復元処理を前記画像に施すことを特徴とする画像処理方法。 Create a restoration filter based on the spatial frequency transfer function of the image output device of the image output destination and a restoration filter based on the visual transfer function,
For each frequency, the spatial frequency transfer function and the visual transfer function are compared, and the spatial frequency transfer function or the visual transfer function is set as a restoration limit,
An image processing method, wherein a restoration process for restoring image quality degradation caused by the image output device is performed on the image using any one of the restoration filters based on the restoration limit.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2009168275A JP5289222B2 (en) | 2009-07-16 | 2009-07-16 | Image processing apparatus and method |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2009168275A JP5289222B2 (en) | 2009-07-16 | 2009-07-16 | Image processing apparatus and method |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JP2011022868A true JP2011022868A (en) | 2011-02-03 |
| JP5289222B2 JP5289222B2 (en) | 2013-09-11 |
Family
ID=43632878
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP2009168275A Expired - Fee Related JP5289222B2 (en) | 2009-07-16 | 2009-07-16 | Image processing apparatus and method |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP5289222B2 (en) |
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US8749659B2 (en) | 2011-08-25 | 2014-06-10 | Canon Kabushiki Kaisha | Image processing program, image processing method, image processing apparatus, and image pickup apparatus |
| US8879872B2 (en) | 2011-06-27 | 2014-11-04 | Samsung Electronics Co., Ltd. | Method and apparatus for restoring resolution of multi-view image |
| JP2015102945A (en) * | 2013-11-22 | 2015-06-04 | キヤノン株式会社 | Creation method of image restoration filter, image processing method, imaging device, and image processing apparatus |
| JP2016192753A (en) * | 2015-03-31 | 2016-11-10 | キヤノン株式会社 | Image processing apparatus and information processing apparatus, and method for the same |
| WO2016194313A1 (en) * | 2015-05-29 | 2016-12-08 | Canon Kabushiki Kaisha | Image processing apparatus, image processing method, and program |
| JP2018011135A (en) * | 2016-07-11 | 2018-01-18 | キヤノン株式会社 | Image processing system and image processing method |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2011024050A (en) * | 2009-07-16 | 2011-02-03 | Canon Inc | Image processing apparatus, and image processing method |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2007183842A (en) * | 2006-01-10 | 2007-07-19 | Tokyo Institute Of Technology | Image restoration filter and image restoration method using the same |
| JP2009042838A (en) * | 2007-08-06 | 2009-02-26 | Ricoh Co Ltd | Image projection method and image projection device |
-
2009
- 2009-07-16 JP JP2009168275A patent/JP5289222B2/en not_active Expired - Fee Related
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2007183842A (en) * | 2006-01-10 | 2007-07-19 | Tokyo Institute Of Technology | Image restoration filter and image restoration method using the same |
| JP2009042838A (en) * | 2007-08-06 | 2009-02-26 | Ricoh Co Ltd | Image projection method and image projection device |
Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US8879872B2 (en) | 2011-06-27 | 2014-11-04 | Samsung Electronics Co., Ltd. | Method and apparatus for restoring resolution of multi-view image |
| US8749659B2 (en) | 2011-08-25 | 2014-06-10 | Canon Kabushiki Kaisha | Image processing program, image processing method, image processing apparatus, and image pickup apparatus |
| JP2015102945A (en) * | 2013-11-22 | 2015-06-04 | キヤノン株式会社 | Creation method of image restoration filter, image processing method, imaging device, and image processing apparatus |
| JP2016192753A (en) * | 2015-03-31 | 2016-11-10 | キヤノン株式会社 | Image processing apparatus and information processing apparatus, and method for the same |
| WO2016194313A1 (en) * | 2015-05-29 | 2016-12-08 | Canon Kabushiki Kaisha | Image processing apparatus, image processing method, and program |
| US10321017B2 (en) | 2015-05-29 | 2019-06-11 | Canon Kabushiki Kaisha | Image processing apparatus for improving image sharpness according to the output condition, image processing method and program |
| JP2018011135A (en) * | 2016-07-11 | 2018-01-18 | キヤノン株式会社 | Image processing system and image processing method |
Also Published As
| Publication number | Publication date |
|---|---|
| JP5289222B2 (en) | 2013-09-11 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| JP5289222B2 (en) | Image processing apparatus and method | |
| JP2006129236A (en) | Ringing eliminating device and computer readable recording medium with ringing elimination program recorded thereon | |
| EP1978724A2 (en) | Method of and apparatus for image denoising | |
| KR101578583B1 (en) | Image processing apparatus, information processing method, and computer-readable storage medium | |
| JP2001500647A (en) | Device profiles for use in digital image processing systems | |
| JP6369019B2 (en) | Image evaluation apparatus and image evaluation program | |
| US6597473B1 (en) | Method to obtain consistent image quality measurements from different image input devices | |
| WO2012098854A1 (en) | Image processing system, image processing method, and image processing program | |
| JP2017050743A (en) | Image processing apparatus, image processing method and program | |
| JP5147903B2 (en) | Image processing apparatus, image processing method, and program | |
| JP5426953B2 (en) | Image processing apparatus and method | |
| US10748252B2 (en) | Method and device for image correction | |
| JP6953183B2 (en) | Image processing equipment, image processing methods and programs | |
| US8639061B2 (en) | Image adjusting circuit and image adjusting method | |
| JPWO2016051716A1 (en) | Image processing method, image processing apparatus, and recording medium for storing image processing program | |
| JP5480102B2 (en) | Image processing apparatus, image forming apparatus, and image processing method | |
| JP6350474B2 (en) | Calibration system, calibration method, image forming apparatus, and calibration program | |
| JP3959547B2 (en) | Image processing apparatus, image processing method, and information terminal apparatus | |
| JP6827838B2 (en) | Imaging equipment and image processing equipment, their control methods, and programs | |
| US20120127535A1 (en) | Image processing apparatus and image processing method | |
| JP2019016222A (en) | Image processing apparatus and control method therefor | |
| JP2014078786A (en) | Image processor, image processing method and recording medium recording image processing method | |
| JP2019140605A (en) | Image processing system, image processing method and program | |
| JP2022067173A (en) | Image processing apparatus, image processing method, and program | |
| JP2006245944A (en) | Device and method for processing image |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| A621 | Written request for application examination |
Free format text: JAPANESE INTERMEDIATE CODE: A621 Effective date: 20120709 |
|
| A977 | Report on retrieval |
Free format text: JAPANESE INTERMEDIATE CODE: A971007 Effective date: 20130430 |
|
| TRDD | Decision of grant or rejection written | ||
| A01 | Written decision to grant a patent or to grant a registration (utility model) |
Free format text: JAPANESE INTERMEDIATE CODE: A01 Effective date: 20130507 |
|
| A61 | First payment of annual fees (during grant procedure) |
Free format text: JAPANESE INTERMEDIATE CODE: A61 Effective date: 20130604 |
|
| LAPS | Cancellation because of no payment of annual fees |