Radiation image processing method which increase and decreases a frequency region of the radiation image

A method of reproducing a radiographic image of a subject by processing radiographic image signals Sorg in a form of a plurality of pixels, wherein each radiographic image signal indicates a signal level corresponding to an amount of radioactive rays transmitted through each portion of the subject, and the radiographic image signals Sorg have a plurality of spatial frequency components depending on level changes between pixels and a signal level range indicating a level difference between a maximum and a minimum signal level, the method comprising the steps of:

• decreasing a response in a low frequency region of the radiographic image signals Sorg, thereby compressing a signal level range of the low frequency region of the radiographic image signals Sorg;
• increasing a response in a high frequency region of the radiographic image signals Sorg, thereby enhancing the high frequency region of the radiographic image signals Sorg;
• obtaining radiographic image signals Sproc by the decreasing and increasing steps to thereby compress and enhance the radiographic image signals and wherein:
• the image signals Sorg when compared with the image signals Sproc, have frequency characteristics which are reduced in a low frequency region thereof that is lower than a predetermined frequency h1 and have frequency characteristics which are enhanced in a high frequency region thereof that is higher than the frequency h1;
• and
• obtaining, for each of said plurality of pixels, unsharp mask signals Sus1 and Sus2 of the image signals Sorg in which a response of the unsharp mask signal Sus1 at the frequency h1 is 0.2 times lower than a value of the image signals Sorg and a response of the unsharp mask signal Sus2 at the frequency h1 is 0.8 times higher than a value of the image signals Sorg, and wherein the image signals Sproc are calculated by use of an equation:
• Sproc=Sorg+f1(Sus1)+f2(Sorg-Sus2)
• wherein f1(Sus1) is a function which decreases as Sus1 increases, and f2(Sorg-Sus2) is a function which increases as (Sorg-Sus2) increases.

A method of reproducing a radiographic image of a subject by processing radiographic image signals Sorg in a form of a plurality of pixels, wherein each radiographic image signal indicates a signal level corresponding to an amount of radioactive rays transmitted through each portion of the subject, and the radiographic image signals Sorg have a plurality of spatial frequency components depending on level changes between each of said plurality of pixels and a signal level range indicating a level difference between a maximum and a minimum signal level, the method comprising the steps of:

• obtaining a first plurality of image signals Sproc1 by providing a signal level range compression to the image signals Sorg to decrease a response in a low frequency region of the image signals Sorg;
• providing a signal level range expansion to enhance a response of an entire frequency region of the first plurality of image signals Sproc1 in accordance with a signal level range of the first plurality of image signals Sproc1;
• and thereafter
• obtaining a second plurality of image signals Sproc2 by providing a gradation treatment to the expanded first plurality of image signals Sproc1,
• wherein the step of providing the signal level range compression comprises:
• obtaining a plurality of unsharp mask signals Sus for each of the plurality of pixels of the image signals Sorg at a low frequency region;
• and
• obtaining the image signals Sproc by use of an equation for the image signals Sorg as follows:
• Sproc=Sorg+f(Sus)
• wherein f(Sus) is a function which decreases as Sus increases.

A method of reproducing a radiographic image of a subject by processing radiographic image signals Sorg in a form of a plurality of pixels, wherein each radiographic image signal indicates a signal level corresponding to an amount of radioactive rays transmitted through each portion of the subject, and the radiographic image signals Sorg have a plurality of spatial frequency components depending on level changes between each of said plurality of pixels and a signal level range indicating a level difference between a maximum and a minimum signal level, the method comprising the steps of:

• obtaining a first plurality of image signals Sproc1' by providing a signal level range expansion to the image signals Sorg to enhance a response of an entire frequency region of the image signals Sorg;
• applying a compressing process to decrease a response of a low frequency region of the first image signals Sproc1 in accordance with a signal level range of the first image signals Sproc1';
• and thereafter
• obtaining a plurality of second image signals Sproc2' by providing a gradation treatment to the compressed first image signals Sproc1',
• wherein the step of applying a compressing process comprises:
• obtaining a plurality of unsharp mask signals Sus for each of the plurality of pixels of the image signals Sorg at a low frequency region;
• and
• obtaining the image signals Sproc by use of an equation for the image signals Sorg as follows:
• Sproc=Sorg+f(Sus)
• wherein f(Sus) is a function which decreases as Sus increases.