1. An image emphasizing apparatus for emphasizing an outline of an image expressed by an input video signal by adding an outline compensation signal to the input video signal so as to sharpen the image expressed by the input video signal, comprising:
an outline component extraction section for extracting from the input video signal an outline component which is a signal component corresponding to the outline of the image;
a threshold value calculation section for calculating a first threshold value, which is used for suppressing excessive emphasis of the outline, and a second threshold value, which is used for emphasizing an outline of a fine detailed image included in the image, the second threshold value being greater than the first threshold value; and
an outline correction section for generating an outline emphasizing signal from the outline component based on the first and second threshold values, and adding the outline emphasizing signal or a gain adjusted outline emphasizing signal, as the outline compensation signal, to the input video signal, thereby generating an output video signal which expresses an image obtained by sharpening the image,
wherein the outline correction section includes:
an emphasizing signal generation section for generating the outline emphasizing signal, the outline emphasizing signal being generated while limiting an absolute value of the outline component so as to be equal to or smaller than the first threshold value when the absolute value of the outline component is equal to or smaller than the second threshold value, and the outline emphasizing signal being generated without limiting the absolute value of the outline component when the absolute value of the outline component is greater than the second threshold value; and
a signal addition section for adding the outline compensation signal generated based on the outline emphasizing signal to the input video signal.
2. An image emphasizing apparatus according to claim 1 wherein:
the emphasizing signal generation section outputs the outline component as the outline emphasizing signal when the absolute value of the outline component is smaller than the first threshold value;
the emphasizing signal generation section generates as the outline emphasizing signal a signal whose absolute value is equal to the first threshold value when the absolute value of the outline component is greater than the first threshold value and is smaller than the second threshold value; and
the emphasizing signal generation section generates a signal by amplifying the outline component as the outline emphasizing signal when the absolute value of the outline component is greater than the second threshold.
3. An image emphasizing apparatus according to claim 1, wherein the outline component extraction section is formed by a high pass filter whose passing band can be controlled externally.
4. An image emphasizing apparatus according to claim 1, further comprising a signal level detection section for detecting a level of the input video signal,
wherein the threshold calculation section calculates the first and second threshold values according to the level detected by the signal level detection section.
5. An image emphasizing apparatus according to claim 4, wherein:
the threshold value calculation section calculates the first threshold value as a value which depends on an externally-supplied first parameter; and
the threshold value calculation section calculates the second threshold value as a value which depends on an externally-supplied second parameter.
6. An image emphasizing apparatus according to claim 4, wherein the signal level detection section detects as the level of the input video signal, an average value of the input video signal averaged over a predetermined period length of the signal level detection section.
7. An image emphasizing apparatus according to claim 1, further comprising an outline detection section for detecting an outline portion that is a signal portion of the input video signal which expresses an outline of the image,
wherein the outline correction section generates the output video signal by adding the outline compensation signal only to the outline portion of the input video signal.
8. An image emphasizing apparatus according to claim 7, further comprising a signal level detection section for detecting a level of the input video signal, wherein:
the threshold calculation section calculates the first and second threshold values according to the level detected by the signal level detection section, and calculates a third threshold value which is used for detecting the outline portion according to the level detected by the signal level detection section; and
the outline detection section compares a variation of the input video signal with the third threshold value, and detects a portion of the input video signal in which a variation of the input video signal is greater than the third threshold value as the outline portion.
9. An image emphasizing apparatus according to claim 8, wherein:
the threshold value calculation section calculates the first threshold value as a value which depends on an externally-supplied first parameter;
the threshold value calculation section calculates the second threshold value as a value which depends on an externally-supplied second parameter; and
the threshold value calculation section calculates the third threshold value as a value which depends on an externally-supplied third parameter.
10. An image emphasizing apparatus according to claim 1, wherein the outline correction section further includes a multiplication section for multiplying the outline emphasizing signal by an externally-supplied coefficient so as to generate the outline compensation signal.
11. An image emphasizing program for emphasizing an outline of original image data by adding an outline compensation component to the original image data so as to sharpen an image expressed by the original image data, the image emphasizing program allowing a computer to perform steps of:
extracting from the original image data an outline component which is a component corresponding to an outline of the image;
calculating a first threshold value which is used for suppressing excessive emphasis of the outline and a second threshold value which is used for emphasizing an outline of a fine detailed image included in the image, the second threshold value being greater than the first threshold value;
generating the outline emphasizing component from the outline component based on the first and second threshold values; and
adding the outline emphasizing component or a gain adjusted component of the outline emphasizing component, as the outline compensation component, to the original image data,
wherein at the step of generating the outline emphasizing component, the outline emphasizing component is generated while limiting an absolute value of the outline component so as to be equal to or smaller than the first threshold value when the absolute value of the outline component is equal to or smaller than the second threshold value, and the outline emphasizing component is generated without limiting the absolute value of the outline component when the absolute value of the outline component is greater than the second threshold value.
12. An image emphasizing program according to claim 11, which further allows the computer to perform a step of sequentially selecting pixels, which form an image expressed by the original image data, as a target pixel, and calculating a value of the target pixel or an average value of a plurality of pixels around the target pixel as an image level, wherein
at the step of extracting the outline component, a component which corresponds to an outline at a position of the target pixel is extracted as the outline component; and
at the step of calculating the thresholds, the first and second threshold values are calculated as values that are conformable to the image level.
13. An image emphasizing program according to claim 11, which further allows the computer to perform a step of sequentially selecting pixels, which form an image expressed by the original image data, as a target pixel, and determining whether or not an outline exists at a position of the target pixel, wherein
at the step of extracting the outline component, a component which corresponds to an outline at a position of the target pixel is extracted as the outline component; and
at the step of adding the outline compensation component, the outline compensation component is added only to a pixel of an image expressed by the original image data in which it is determined that an outline exists.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A sheet processing apparatus comprising:
a first roller;
a driving member that has a drive source for generating a driving force and which rotates the first roller by the driving force of the drive source;
a first opposite roller that forms a first nip portion along with the first roller;
a second roller provided on a downstream side in a sheet feeding direction from the first roller;
a second opposite roller that forms a second nip portion along with the second roller; and
a load unit that applies a load torque to the first roller,
wherein at least one of the first nip portion and second nip portion is shorter than a maximum length of a sheet that can be conveyed in a main body of the apparatus in a width direction perpendicular to the feeding direction, and
the load unit applies a tension in the sheet feeding direction to the sheet fed between the first and second nip portions after the sheet fed by the first nip portion is nipped in the second nip portion.
2. The sheet processing apparatus according to claim 1, wherein the first and second nip portions are provided in a center area of the fed sheet in the width direction.
3. The sheet processing apparatus according to claim 1, further comprising a drive control unit that controls the driving member,
wherein the drive control unit prevents a driving force of the drive source from being transmitted to the first roller after the sheet fed by the first nip portion is nipped in the second nip portion.
4. The sheet processing apparatus according to claim 3, wherein the drive control unit has a clutch which prevents a driving force of the drive source from being transmitted to the first roller.
5. The sheet processing apparatus according to claim 1, wherein said driving member is a first driving member, and further comprising a second driving member that rotates the second roller,
wherein a circumferential velocity of the second roller rotated by the second driving member is faster than a circumferential velocity of the first roller rotated by the first driving member.
6. The sheet processing apparatus according to claim 1, further comprising a one-way clutch provided between the drive source and the first roller.
7. The sheet processing apparatus according to claim 1, wherein the load unit has a torque limiter.
8. The sheet processing apparatus according to claim 1, wherein a length in the width direction of at least one of the first roller, the first opposite roller, the second roller, and the second opposite roller is shorter than the maximum length of the width direction of the sheet.
9. The sheet processing apparatus according to claim 1, wherein, in an outer diameter of at least one of the first roller, the first opposite roller, the second roller, and the second opposite roller, a center portion of a rotational axis direction is larger than an edge portion of the rotational axis direction.
10. The sheet processing apparatus according to claim 1, further comprising a pressure release unit that releases a pressure of the first opposite roller applied to the first roller,
wherein the first opposite roller has a pressure release state to the first roller by the pressure release unit before a sheet is nipped in the second nip portion, and
the first opposite roller has a pressure state to the first roller by the pressure release unit after a sheet is nipped in the second nip portion.
11. The sheet processing apparatus according to claim 1, further comprising a sheet detection unit that detects a sheet with a predetermined distance toward an upstream side in a sheet feeding direction from the second nip portion,
wherein it is determined whether or not a sheet is nipped in the second nip portion based on a predetermined distance from the sheet detection unit to the second nip portion and a feeding velocity of the sheet.
12. The sheet processing apparatus according to claim 1, further comprising a moisture adding unit that adds moisture to a sheet,
wherein the moisture adding unit is arranged on an upstream side of the sheet in a sheet feeding direction from the first and second rollers.
13. The sheet processing apparatus according to claim 12, wherein the moisture adding unit adds more moisture to a center portion of a width direction perpendicular to the sheet feeding direction than both edge portions.
14. The sheet processing apparatus according to claim 12, wherein the moisture adding unit adds moisture only to a center portion of a width direction perpendicular to the sheet feeding direction.
15. The sheet processing apparatus according to claim 12, wherein the moisture adding unit has an applying roller that applies a liquid to a sheet and has a liquid retaining member that retains a liquid in a liquid retaining space formed to abut on the applying roller, and
a liquid supplied to a surface of the applying roller is applied from the liquid retaining member by rotating the applying roller.
16. The sheet processing apparatus according to claim 12, further comprising a conveyance path that guides a sheet approximately vertically from an upper side to a lower side,
wherein the moisture adding unit and the first roller and second roller are sequentially arranged in the conveyance path.
17. The sheet processing apparatus according to claim 1, further comprising a curl correction unit that corrects a curl in a sheet,
wherein the curl correction unit is arranged on a downstream side in the sheet feeding direction from the second roller.
18. The sheet processing apparatus according to claim 17, wherein the curl correction unit corrects a curl by nipping and conveying a sheet through a curved nip portion formed by causing an elastic roller and a rigid roller to make pressed contact.
19. The sheet processing apparatus according to claim 17, wherein the curl correction unit corrects a curl by nipping and conveying a sheet in a curved nip portion formed by causing an endless belt stretching around a plurality of rollers and a rigid roller to make pressed contact.
20. The sheet processing apparatus according to claim 17, wherein the curl correction unit has a first curl correcting portion that corrects a curl protruding toward one surface side of a sheet and second curl correcting portion that corrects a curl protruding toward the other surface side of the sheet.
21. The sheet processing apparatus according to claim 1, further comprising a sheet drying unit that dries a sheet,
wherein the sheet drying unit is arranged on a downstream side in the sheet feeding direction from the second roller.
22. The sheet processing apparatus according to claim 21, wherein the sheet drying unit is a fan.
23. The sheet processing apparatus according to claim 21, wherein the sheet drying unit is a drier having a fan and a heater.
24. The sheet processing apparatus according to claim 21, wherein the sheet drying unit is provided in each of one surface side and an other surface side of a sheet.
25. An image forming system comprising:
an image forming apparatus having a transfer portion that transfers a toner image onto a sheet and a fixing portion that fixes the transferred toner image on a sheet by heating the transferred toner image; and
a sheet processing apparatus that is detachably connected to the image forming apparatus and performs a processing for the sheet discharged from the image forming apparatus,
wherein the sheet processing apparatus is the sheet processing apparatus according to claim 1.