JP4969135B2 - Image adjustment method - Google Patents

Description

  The present invention relates to methods and systems for enhancing display brightness, contrast and other performance.

1A and 1B are diagrams showing a conventional backlight LCD (liquid crystal display) system. FIG. 1A shows an example using a fluorescent lamp 2 as a backlight light source, and FIG. 1B shows an LED 10 as a backlight light source. Here is an example used: As is well known, light from the light source 2 or 10 is dispersed by the diffuser 4, supplied to the LCD polarizing layer 6, and viewed through the LCD pixel 8.
A typical display device displays images using a fixed range of luminescence levels. For many displays, the luminescence range has 256 levels evenly spaced from 0 to 255. Image code values are generally assigned directly to these levels.

  In many electronic devices with large displays, the display has become a major power consuming component. For example, in a laptop computer, the display is likely to consume more power than any other component in the system. Many displays with limited power usage, such as those found in battery-powered devices, use several illumination, or brightness levels, to help manage power consumption. it can. Some systems can use full power mode when plugged into a power source, eg, AC power source, and can use power save mode when operating on battery power.

  In some devices, the display can automatically enter a power saving mode, in which the display illuminance is reduced to avoid wasting power. These devices can have a number of power saving modes that gradually reduce the illuminance. Generally, when the illuminance of the display is lowered, the image quality is similarly lowered. Decreasing the maximum brightness level also reduces the dynamic range of the display and causes image contrast problems. Accordingly, contrast and other image quality are degraded during operation of a typical power saving mode.

  Many display devices, such as liquid crystal displays (LCD) or digital micromirror devices (DMD), use light valves that are backlit, sidelighted or frontlit from one or another direction. In a backlight valve display such as an LCD, a backlight is located behind the liquid crystal panel. The backlight emits light through the LC panel, which modulates the light to match the image. Color displays can modulate luminescence and color. Individual LC pixels modulate the amount of light sent from the backlight through the LC panel to the user's eyes or other object. In some cases, the object can be an optical sensor, such as a charge coupled device (CCD).

  In some displays, a light emitter can also be used to align the images. These displays, such as light emitting diode (LED) displays and plasma displays, use pixels that emit light rather than reflect light from another light source.

  The first technical means of the present invention includes applying a tone scale adjustment model to an image to generate a tone scale adjusted image, and a gain map function to generate an adjusted image with enhanced gain. Applying to the tone scale adjusted image.

  A second technical means for applying a tone scale adjustment model to the image to generate a tone scale adjusted image; calculating a high pass image and a low pass image from the tone scale adjusted image; Applying a gain map function to the high-pass image to generate a modified high-pass image, and adding the low-pass image to the adjusted high-pass image to form an enhanced image. It is characterized by.

  Some embodiments of the invention alter the luminescence modulation level of light valve modulated pixels to compensate for reduced light source illumination intensity or to improve image quality at a fixed light source illumination level. Relates to a system and method.

  Some embodiments of the invention can also be used with displays that use light emitters to align images. These displays, such as light emitting diode (LED) displays and plasma displays, use pixels that emit light rather than reflect light from another light source. Embodiments of the present invention are used to enhance the images produced by these devices. In these embodiments, the brightness of the pixels can be adjusted to enhance the dynamic range, luminescence range, and other image subdivision of a particular image frequency band.

  These and other objects, features and advantages of the present invention will be more readily understood when the following detailed description of the invention is examined with reference to the accompanying drawings.

  The embodiments of the present invention can be best understood with reference to the drawings. Throughout the drawings, like parts are indicated by like numbers. The drawings are incorporated as part of the following detailed description.

  It will be readily appreciated that the portions of the invention generally described and illustrated herein can be arranged and designed in a wide variety of different structures. Accordingly, the following more detailed description of embodiments of the method and system of the present invention is not intended to limit the scope of the invention, but merely to presently preferred embodiments of the invention.

  Elements of embodiments of the present invention can be implemented in hardware, firmware and / or software. Although the embodiments disclosed herein may describe only one of these forms, those skilled in the art should understand that these elements can be implemented in any of these forms within the scope of the present invention. It is.

  Display devices that use light valve modulators, such as LC modulators and other modulators, can reflect light, which emits light in the front (facing the viewer (hereinafter referred to as the viewer)). After passing through the modulation panel layer, it is arranged to return to the viewer again. The display device is also transmissive where light is emitted to the back of the modulation panel layer and can travel through the modulation layer to the viewer. There are also display devices that are reflective and transmissive that combine reflective and transmissive capabilities. In this device, light can travel from the back through the modulation layer to the front, while light from another light source is reflected after entering from the front of the modulation layer. In either of these cases, elements in the modulation layer, such as individual LC elements, can control the perceivable brightness of a pixel.

  In backlight, front light, and sidelight displays, the light source can be a series of fluorescent tubes, LED arrays, or other light sources. If the display is larger than the typical size of about 18 inches, the majority of the power consumption for the device is the power consumed by the light source. It is important to reduce power consumption for certain applications and in certain markets. However, reducing the power means reducing the luminous flux of the light source, and thus reducing the maximum brightness of the display.

The basic equations for the current gamma corrected light valve modulator gray level code value, CV, light source level L _source and output light level L _out are as follows:

  Where g is the calibration gain, dark is the dark level of the light valve, and ambient is the light incident on the display from room conditions. From this equation, it can be seen that if the light source for the backlight is reduced by x%, the light output is also reduced by x%.

  By changing the modulation values of the light valve, in particular by increasing these values, a reduction in the light source level can be compensated. In practice, light levels below (1-x%) can be correctly reproduced, but light levels above (1-x%) cannot be reproduced without increasing the intensity of the additional light source or light source.

  Setting the light output from the original reduced light source gives a basic code value correction that can be used to correct the code value for x% reduction (assuming dark and ambient are zero). It is done. The code values are as follows:

  FIG. 2A illustrates this adjustment, and in FIGS. 2A and 2B, the original display values correspond to points along line 12. When the backlight or light source is in power saving mode and the light source illumination is reduced, the display code value must be increased so that the light bulb can act against the light source illumination reduction . These increased values correspond to points along line 14. However, as a result of such adjustment, the code value 18 is greater than a value that the display can generate (eg, 255 for an 8-bit display). These values are therefore clipped (20) as shown in FIG. 2B. The image adjusted in this way may have the problem that highlights are washed out, looks unnatural, and generally the image quality deteriorates.

  When such a simple adjustment model is used, a code value below the clipping point 15 with a luminescence level equal to the level generated by the full power light source (in this embodiment) while in the reduced light source illumination mode. Then, the input code value 230) is displayed. The same luminescence is generated even at low power that causes power saving. When the set of image code values is limited to a range below the clipping point 15, the power saving mode can be activated without the user being aware. Unfortunately, if the code value exceeds the clipping point 15, the luminescence is reduced and details are lost. Embodiments of the present invention can change the LCD or light valve code value and provide a high brightness (or no brightness reduction in power saving mode) algorithm while reducing clipping artifacts that can occur at the high end of the luminescence range. .

  A book that eliminates the reduction in brightness associated with reducing the power of the light source of the display by matching the image luminescence displayed at low power with the image luminescence displayed at full power for a large range of values. There are also embodiments of the invention. In these embodiments, the light source or backlight power reduction that divides the output luminescence by a specific factor is compensated by increasing (boosting) the image data by a reciprocal factor.

  By ignoring the limitation of the dynamic range, an image displayed at full power and an image displayed at low power can be made the same. This is because division (for reduced light source illumination) and multiplication (for increased code values) substantially cancels over a large range. Clipping artifacts can occur due to dynamic range limitations whenever the multiplication of image data (for increasing code values) exceeds the maximum value of the display. Clipping artifacts caused by dynamic range limitations can be eliminated or reduced by rolling off the increase at the top of the code value. This roll-off can be started at the maximum fidelity point (MFP), beyond which the luminescence cannot match the original luminescence.

In some embodiments of the present invention, the following steps can be performed to compensate for light source illumination reduction or virtual reduction for image enhancement.
1) Determine the reduction level of the light source (backlight) converted to the percent reduction in luminescence.
2) Determine the maximum fidelity point (MFP) at which roll-off from coincidence of low power output and full power output occurs
3) Determine the compensation tone scale operator.
a. Below the MFP, the tone scale is increased to compensate for the decrease in luminescence of the display.
b. Above the MFP, the tone scale is gradually rolled off (in some embodiments, a continuous differential value is maintained).
4). Apply the tone scale mapping operator to the image,
5. Send this to the display.

  The main advantage of these embodiments is that power savings can be achieved with only minor changes to narrow category images. (The only difference is above the MFP, which is that the peak brightness decreases and some bright details are lost). Image values below the MFP can be displayed in a power saving mode with the same luminescence as the full power mode, which makes these image regions indistinguishable from the full power mode.

  In some embodiments of the invention, a tone scale map can be used that depends on power reduction and display gamma values, but not on image data. These embodiments have two advantages. The first advantage is that flicker artifacts caused by processing the frames do not occur, and the second advantage is that the implementation complexity of the algorithm is very low. In some embodiments, offline tone scale design and online tone scale mapping can be used. By specifying the MFP, it is possible to control highlight clipping reduction.

  The features of the embodiment of the present invention can be described with reference to FIG. FIG. 3 is a graph showing image code values plotted against luminescence in several situations. A first curve 32, indicated by a dotted line, shows the original code value for a light source operating at 100% power. A second curve 30 indicated by the dashed line curve shows the luminescence of the original code value when the light source operates at 80% of full power. A third curve 36, shown as a dotted curve, shows the luminescence as the code value is increased to match the luminescence provided at 100% source illumination when the light source operates at 80% of full power. Show. A fourth curve 34, shown as a solid line, shows the data increased with the roll-off curve to reduce the effect of clipping at the high end of the data.

  In this embodiment shown in FIG. 3, the MFP 35 with a code value of 180 is used. Below the code value 180, the increased curve 34 matches the luminescence output 32 with the original 100% power display. Above 180, the increasing curve smoothly transitions to the maximum output possible with 80% display. This smoothness reduces clipping and quantization artifacts. In some embodiments, the tone scale function can be defined in pieces in order to smoothly match at the transition point indicated by the MFP 35. Below the MFP 35, an increased tone scale function can be used. Above the MFP 35, the curve is smoothly fitted to the end point of the tone scale curve increased in the MFP, and is fitted to the end point 37 with the maximum code value “255”. In some embodiments, the slope of the curve can be matched to the increased tone scale curve / line slope in MFP 35. This means that the differential value of the line and the differential value of the curve function in the MFP are made equal, and the line value and the curve function value at that point are matched, so that the slope of the line below the MFP and the curve above the MFP This can be achieved by matching the slope of. Another limitation on the curve function is to force the maximum point “255, 255” 37 to pass. In some embodiments, the slope of the curve can be set to 0 at the maximum value point 37, and in another embodiment, an MFP value of 180 can correspond to a light source power reduction rate of 20%.

  In some embodiments of the invention, a tone scale curve can be defined by a linear relationship with gain g below the maximum fidelity point (MFP). A further tone scale can be defined above the MFP so that this curve and the first derivative are continuous at the MFP. This continuity means the next form of tone scale function.

  The gain can be determined by the display gamma value and the luminance reduction ratio as follows.

In some embodiments, the value of the MFP can be tuned by manually balancing the preservation of the highlight details and the absolute brightness.
An MFP can be determined by imposing a restriction that the inclination is 0 at the maximum point. This means that:

  In some embodiments, the following equation can be used to calculate the code value and the increment data for simple increment data with clipping data and correction data, respectively:

  The constants A, B, and C are selected so that the MFP can smoothly fit so that the curve passes through the points “255, 255”. FIG. 4 shows a plot of these functions.

  FIG. 4 is a plot diagram showing the relationship between the original code value and the adjusted code value. The original code values are shown as points along the original data line 40, which indicate a 1: 1 relationship between the adjusted values and the original values without adjustment. According to embodiments of the present invention, these values can be increased or adjusted to indicate higher luminescence levels. A simple increase procedure according to the “tone scale increase” equation results in a value along the increase line 42. Displaying these values results in the clipping shown graphically as line 46 and represented by the equation in the “tone scale clipped” equation above, so the adjustment is from the maximum fidelity point 45 along curve 44 to the maximum value. The taper can be reduced to point 47. In some embodiments, this relationship can be mathematically taught with the above “tone scale corrected” equation.

  Using these concepts, the luminescence value displayed by the display when the light source is operating at 100% power can be displayed by the display when the light source is operating at a lower power level. This is accomplished by an increase in tone scale that further opens the light valve substantially to compensate for the illumination loss of the light source. However, simply applying such an increase over the entire code value range results in clipping artifacts at the high end of the range. To prevent or reduce these artifacts, the tone scale function can be rolled off smoothly. Such roll-off can be controlled by MFP parameters. A large value of the MFP matches the luminescence over a wide interval, but increases the quantization / clipping artifacts that can be seen at the high end of the code value.

  Embodiments of the invention can operate by adjusting the code value. In a simple gamma display model, the scaling of code values gives the scaling of luminescence values with different scale factors. To determine whether such a relationship is maintained in a more realistic display model, a gamma offset gain-flare (GOG-F) model can be considered. Backlight power scaling corresponds to a linear reduction equation, where the percentage p is applied to the output of the display rather than ambient. It has been found that reducing the gain by a factor p is equivalent to leaving the gain unchanged and scaling the data, code value and offset by a factor determined by the display gamma. If it can be mathematically modified appropriately, a multiplication factor can be drawn into the power function. This deformation factor can scale both code values and offsets.

  With reference to FIG. 5, some embodiments of the present invention can be described. In these embodiments, the tone scale adjustment can be designed or calculated offline prior to image processing, or the adjustment may be designed and calculated online during image processing. The tone scale adjustment 56 can be designed and calculated based on at least one of the display gamma 50, the efficiency factor 52, and the maximum fidelity point (MFP) 54, regardless of the timing of operation. These factors can be processed by the tone scale design process 56 to create a tone scale adjustment model 58. This tone scale adjustment model may take the form of an algorithm, a look-up table (LUT) or other model that can be applied to image data.

  Once the adjustment model 58 is created, it can be applied to the image data. The application of this adjustment model can be described with reference to FIG. In these embodiments, an image is input (62) and a tone scale adjustment model 58 is applied to the image (64) to adjust the image code value. This process results in an output image 66 that can be sent to the display. The tone scale adjustment application 64 is generally an online process, but may be performed prior to image display if conditions permit.

  Some embodiments of the present invention include systems and methods for enhancing images displayed on displays using light emitting pixel modulators such as LED displays, plasma displays, and other types of displays. These same systems and methods can be used to enhance images displayed on displays that use light valve pixel modulators with light sources operating in full power mode or otherwise.

  These embodiments operate in the same way as the previously described embodiments, but rather than compensate for the reduced light source illumination, these embodiments simply reduce the luminance of the pixel range as if the light source had been reduced. It only increases. In this way, the overall brightness of the image is improved.

  In these embodiments, the original code value is increased over a large range of values. As described above with respect to the other embodiments, such adjustment of the code value can be executed, except that the actual illumination amount of the light source is not reduced. Thus, the image brightness increases significantly over a wide range of code values.

  With reference to FIG. 3, some of these embodiments can be similarly described. In these embodiments, the code values for the original image are shown as points along the curve 30, and these values can be increased or adjusted to values with higher luminescence levels. These increased values can be displayed as points along the curve 34, which extends from the zero point 33 to the maximum fidelity point 35 and then gradually decreases in slope to the maximum value point 37.

  Some embodiments of the invention include an unsharp masking method. In some of these embodiments, unsharp masking can use a spatially varying gain. Such a gain can be determined by the value of the image and the slope of the modified tone scale curve. In some embodiments, the use of a gain array allows matching of image contrast even when image brightness cannot be reproduced due to display power limitations.

Some embodiments of the invention may take the following process steps.
1. Calculate tone scale adjustment model.
2. Calculate high-pass image.
3. Calculate the gain array.
4). The high pass image is weighted by gain.
5. The low-pass image and the weighted high-pass image are added.
6). Send to display.
Another embodiment of the invention may take the following process steps.
1. Calculate tone scale adjustment model.
2. Compute a low-pass image.
3. The high pass image is calculated as the difference between the image and the low pass image.
4). The gain array is calculated using the image values and the slope of the modified tone scale curve.
5. Weight high-pass image with gain.
6). The low-pass image and the weighted high-pass image are added.
7). Send to a display with reduced power.

  By using some embodiments of the present invention, power savings can be achieved with only a small change in a narrow category of images. (A difference occurs only above the MFP, which consists of a reduction in peak brightness and loss with bright details). Image values below the MFP can be displayed in a power saving mode with the same luminescence as the full power mode, which makes these image regions indistinguishable from the full power mode. Other embodiments of the invention can improve this performance by reducing the loss of bright details.

  These embodiments can include spatially varying unsharp masking to preserve bright details. As with other embodiments, both online and offline components can be used. In some embodiments, off-line components can be extended by calculating a gain map in addition to the tone scale function. The gain map is based on image values and can specify a non-sharp filter gain to apply. The gain map value can be determined using the slope of the tone scale function. In some embodiments, the gain map value at a particular point “P” can be calculated as the ratio of the slope of the tone scale function below the MFP to the slope of the tone scale function at point “P”. In some embodiments, the tone scale function is linear below the MFP, so the gain is in units below the MFP.

  With reference to FIG. 7, some embodiments of the present invention can be described. In these embodiments, tone scale adjustments can be designed or calculated offline prior to image processing, or adjustments can be designed and calculated online during image processing. Regardless of the timing of operation, tone scale adjustment 76 may be designed or calculated based on at least one of display gamma 70, efficiency factor 72, and maximum fidelity point (MFP) 74. These factors can be processed by the tone scale design process 76 to create a tone scale adjustment model 78. This tone scale adjustment model may take the form of an algorithm, a look-up table (LUT) or some other model that can be applied to image data as described in connection with the other embodiments above. In these embodiments, a separate gain map 77 is also calculated (75). The gain map 77 can be applied to a specific image sub-division, for example, a frequency range. In some embodiments, a gain map can be applied to the frequency-divided portion of the image, and in some embodiments, a gain map can be applied to the high-pass image sub-partition, and a specific image frequency range or other image sub- A gain map can also be applied to the division.

  An example of the tone scale adjustment model will be described with reference to FIG. In these embodiments, a function transient point (FTP) 84 (similar to the MFP used in the embodiment that compensates for light source reduction) is selected to provide a first gain relationship 82 for values below FTP 84. Select. In some embodiments, the first gain relationship can be a linear relationship, but other relationships and functions may be used to convert the code value to an enhanced code value. A second gain relationship 86 can be used above the FTP 84. The second gain relationship 86 can be a function that joins the FTP 84 and the maximum value point 88. In some embodiments, the second gain relationship 86 can match the value and slope of the first gain relationship 82 in FTP 84 and can pass through a maximum value point 88. Other relationships and other relationships described above with reference to other embodiments can also operate as the second gain relationship 86.

  In some embodiments, the gain map 77 can be calculated in connection with a tone scale adjustment model as shown in FIG. An example of the gain map 77 will be described with reference to FIG. In these embodiments, the gain map function is related to the tone scale adjustment model 78 as a function of the slope of the tone scale adjustment model, and in some embodiments, the value of the gain map function at a particular code value is: It is determined by the ratio of the slope of the tone scale adjustment model at a code value below FTP to the slope of the tone scale adjustment model at this specific code value. In some embodiments, this relationship can be expressed mathematically in the following equation:

  In these embodiments, the gain map function is equal to a function below FTP such that the tone scale adjustment model causes a linear increase. As the slope of the tone scale adjustment model gradually decreases for code values above FTP, the gain map function increases rapidly. Such a sharp increase in the gain map function enhances the contrast of the image portion to which this function is applied.

  Example of tone scale adjustment factor shown in FIG. 8 and gain map function shown in FIG. 9 using 80% display percentage (light source reduction), 2.2 display gamma and 180 maximum fidelity points Calculated examples.

  In some embodiments of the invention, an unsharp masking operation can be applied to follow the application of the tone scale adjustment model. In these embodiments, artifacts can be reduced by unsharp masking techniques.

  With reference to FIG. 10, some embodiments of the present invention will be described. In these embodiments, the original image 102 is input and the tone scale adjustment model 103 is applied to this image. The original image 102 is also used as input to the gain mapping process 105 that produces a gain map. Next, the tone scale adjusted image is processed through the low pass filter 104, resulting in a low pass adjusted image. Next, the low-pass adjusted image is subtracted from the tone scale adjusted image (106) to generate a high-pass adjusted image. The high pass adjusted image is then multiplied 107 with the appropriate value in the gain map to provide a gain adjusted high pass image that is then converted to the low pass adjusted image. Add (108). This low-pass-adjusted image has already been adjusted by the tone scale adjustment model. As a result of this addition, an output image 109 with increased brightness and improved high-frequency contrast is obtained.

  In some of these embodiments, for each component of each pixel of the image, the gain value is determined from the gain map and the value of the image at that pixel. The original image 102 prior to applying the tone scale adjustment model can be used to determine the gain. Each component of each pixel of the high pass image can also be scaled by a corresponding gain value before being added back to the low pass image. At the point where the gain map function is 1, the image value is not changed by the unsharp masking operation. At points where the gain map function exceeds 1, the contrast is increased.

  Some embodiments of the invention resolve the loss of contrast in high-end code values when the code value brightness is increased by decomposing the image into multiple frequency bands. In some embodiments, a tone scale function may be applied to the low pass band to increase the brightness of the image data, compensate for the decrease in light source luminescence at low power settings, or simply increase the brightness of the displayed image. it can. In parallel with this, a constant gain is applied to the high pass band, and the contrast of the image can be preserved even in an area where the average absolute luminance is reduced due to a smaller display power. An example operation of the algorithm is shown as follows.

1. Perform frequency resolution of the original image.
2. Apply brightness preservation and tone scale map to low-pass image.
3. A constant multiplier is applied to the high pass image.
4). The low pass image and the high pass image are added.
5. Send the result to the display.

  By matching the luminosity between the full power display of the original image and the low power display of the process image for light source lighting reduction applications, the tone scale function and constant gain can be determined offline. The tone scale function can also be determined offline for brightness enhancement applications.

  For a suitable MFP value, these constant high-pass gain embodiments and unsharp masking embodiments can hardly be distinguished by their performance. These constant high pass gain embodiments have three main advantages over the unsharp masking embodiment. That is, it is less affected by noise, can use a larger MFP / FTP, and can use current processing steps in the display system. The unsharp masking embodiment uses a gain that is the reciprocal of the slope of the tone scale curve, and when the slope of this curve is small, this gain leads to large amplification noise. This noise amplification can also impose practical limits on the size of the MFP / FTP. The second advantage is that it can be extended to any MFP / FTP value. A third advantage comes from examining the algorithm settings in the system, both the constant high-pass gain embodiment and the unsharp masking embodiment use frequency decomposition. Constant high-pass gain embodiments first perform such operations, while some unsharp masking embodiments first apply a tone scale function prior to frequency resolution. Some system processes, such as inverse contouring, perform frequency decomposition prior to the luminance preservation algorithm. In these cases, some constant high-pass embodiments use such frequency decomposition, and thus the conversion step can be omitted, while some unsharp masking embodiments invert the frequency decomposition and use the tone scale function. And another frequency decomposition must be performed.

  Some embodiments of the present invention prevent loss of contrast in high-end code values by dividing the image based on spatial frequency prior to application of the tone scale function. In these embodiments, a tone scale function with roll-off can be applied to the low-pass (LP) component of the image. In a light source illumination reduction compensation application, this results in an overall luminescence match of the low pass image components. In these embodiments, the high pass (HP) component is increased uniformly (constant gain). The frequency-divided signals can be recombined and clipped as necessary. The high pass component does not pass the tone scale function roll-off, so detail is preserved. A smooth roll-off of the low pass tone scale function saves headroom for adding increased high pass contrast. Clipping that can occur in such final combinations has not been shown to significantly reduce detail.

  Next, some embodiments of the present invention will be described with reference to FIG. These embodiments comprise a frequency division or decomposition step 111, a low pass tone scale mapping step 112, a constant high pass gain step or increase step 116, and an enhanced image component addition or recombination step 115.

  In these embodiments, the input image 110 is decomposed into spatial frequency bands. In an embodiment using two bands, such a decomposition can be performed using a low pass (LP) filter 111. Frequency division is performed by calculating the LP signal through the low pass filter 111 and subtracting (113) the LP signal from the original signal to form a high pass (HP) signal 118. In an embodiment, a spatial 5 × 5 rect filter can be used for this decomposition, but another filter may be used.

  As described in the previous embodiments, the LP signal can then be processed by applying tone scale mapping. In an embodiment, this process can be accomplished using a luminosity matching LUT. In these embodiments, most of the details have already been extracted in the filtering step 111 so that higher values of MFP / FTP can be used compared to some previously unsharp masking embodiments. In general, clipping should not be used because some headroom to which contrast should be added should be preserved.

  In some embodiments, MFP / FTP can be determined automatically and MFP / FTP can be set so that the slope of the tone scale curve is zero at the upper limit. FIG. 12 shows a series of tone scale functions determined in this way. In these embodiments, the maximum MFP / FTP value can be determined so that the tone scale function is 255 and the slope is zero. This maximum value is the maximum MFP / FTP value that does not cause clipping.

  In some embodiments of the invention described with reference to FIG. 11, the processing of the HP signal 118 is independent of the MFP / FTP selection used to process the low pass signal. The HP signal 118 is processed with a constant gain 116 that preserves contrast when the power / light source illumination is reduced or the image code value is increased to improve brightness. The formula for the gain 116 of the HP signal in terms of full backlight power and reduced backlight power (BL) and display gamma value is then shown as a high pass gain equation. Since the gain is generally small (eg, the gain is 1.1 for an 80% power reduction and a gamma value of 2.2), the increase in HP contrast is robust to noise.

  In some embodiments, once the tone scale mapping 112 is applied to the LP signal and the constant gain 116 is applied to the HP signal by LUT processing or other methods, these frequency components are added (115). In some cases, you can clip. Clipping is required when the increased HP value added to the LP value exceeds 255. This is generally true only for high contrast luminance signals. In some embodiments, the tone scale LUT structure ensures that the LP signal does not exceed the upper limit. Although the HP signal may cause clipping when added, the negative value of the HP signal is not clipped even when clipping occurs, and a part of contrast can be maintained.

  The terms and expressions used so far in the specification are terms used to describe the invention and are not used as limiting terms for the invention. In using such terms and expressions, the characteristics and features described and illustrated in the specification It does not exclude some equivalents. The scope of the invention is defined and limited only by the claims.

It is a figure which shows the conventional backlight LCD system which uses the fluorescent lamp as a light source. It is a figure which shows the conventional backlight LCD system which uses LED as a light source. 6 is a graph showing a relationship between an original image code value and an increased image code value. It is a graph which shows the relationship between the original image code value and the image code value increased by clipping. Fig. 6 is a graph showing the luminance levels associated with code values for various code value modification schemes. It is a graph which shows the relationship between the original image code value and the image code value changed according to various change methods. It is a figure which shows an example of tone scale adjustment model generation. It is a figure which shows an example of application of a tone scale adjustment model. It is a figure which shows an example of a tone scale adjustment model, and the example of a gain map production | generation. It is a graph which shows an example of a tone scale adjustment model. It is a graph which shows an example of a gain map. It is a flowchart which shows an example of the process which applied the tone scale adjustment model and the gain map to the image. 6 is a flowchart illustrating an example of a process for applying a tone scale adjustment model to a frequency band of an image and applying a gain map to another frequency band of the image. It is a graph which shows the change of the tone scale adjustment model when MFP changes.

Explanation of symbols

2 ... fluorescent backlight system, 4 ... diffuser, 8 ... LCD pixel, 10 ... LED backlight array.

Claims (7)

a) generating first image data in which the code value is adjusted by converting the code value of the image data using a tone scale adjustment model;
b) Obtained by applying a low pass filter to the first image data to form a low pass component of the first image data, and subtracting the low pass component of the first image data from the first image data. A gain of a code value of the second image data is determined using a gain map function, and third image data in which the code value is adjusted using the determined gain is generated from the second image data; Generating fourth image data by adding a low-pass component of the first image data to third image data ,
The step of generating the first image data includes a first step of adjusting a gain of a code value in a first range below a pre-designated code value, and a step above the pre-designated code value. and a second step of increasing the code value of the second range of the tone scale adjustment model consists line graph and curve graph, the straight line graph, first before the adjustment of gain in the first step The code value of the first range after the gain adjustment for the code value of the range of 1 is shown, and the curve graph shows the second value after the increase with respect to the code value of the second range before the increase. The code value of the range is shown, and the slope of the tangent gradually decreases as the code value of the second range before the increase increases, and according to the curve graph, the increase amount of the code value of the second range is Determined The minimum value of the code value of the second range after the increase indicated by the curve graph is consistent with the value obtained by adjusting the gain in said first step with respect to pre-specified code value, the The maximum value of the code value in the second range after the increase indicated by the curve graph coincides with the maximum value of the code value that can be set in the display process on the display ,
The gain map function is a gain used in the step of generating the third image data, when a certain code value is input, a ratio of the slope of the straight line graph to the slope of the tone scale adjustment model at the code value. An image adjustment method characterized by being a function to be output as   The image adjustment method according to claim 1, wherein the adjustment of the gain of the code value in the first range is an adjustment in which a gain multiplied by the code value of the first range is a constant gain.   The image adjustment method according to claim 1, wherein the gain map function depends on at least one of a display gamma, an efficiency factor, and the pre-specified code value.   In the first range, the slope of the graph indicating the code value after the gain is adjusted with respect to the code value before the gain is adjusted in the predetermined code value is specified in the curve graph. The image adjustment method according to claim 1, wherein the image value matches a slope of a tangent in the code value.   2. The image adjustment method according to claim 1, wherein the tangent in the curve graph has a slope of 0 at a point where the code value of the second range after the increase becomes a maximum value. In the first step, using a first function to adjust the gain of the code values of the first range, the pre-Symbol second step, the gain with respect to the pre-specified code value A code value in the second range by using a second function that changes the code value in the second range from the value obtained by the adjustment to the maximum code value that can be set in the display process on the display. The image adjustment method according to claim 1, wherein: Before SL gain map function, the gain code value contained in said first range and constant regardless of the code value, the gain code value contained in said second range according to the increase of the code value wherein the Ru function der to increase, an image adjustment method according to claim 1.

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