Abstract:
A method for displaying images in a display apparatus is provided herein. In the display apparatus, an image is displayed during each frame period of a plurality of contiguous frames. At first, original images are received, and each of the received original images is composed of M number of contiguous image rows. A predetermined amount of frame periods are grouped as a frame group. During each frame period, one of M number of image rows is selected as an initial image row. From the initial image row, N number of image rows are selected from the M number of image rows according to an image row selection rule to constitute an image for displaying. In each frame group, at least two different initial parameters are used within two frame periods in order to output different images.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of Taiwan application serial no. 96103502, filed Jan. 31, 2007. All disclosure of the Taiwan application is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates to a display apparatus. More particularly, the present invention relates to an image display method for adjusting image size. 
     2. Description of Related Art 
     At present, most of the portable consumer devices are at least equipped with a LCD (Liquid Crystal Display). When user views contiguous images, since human vision system can adapt to and adjust itself to the quickly updated frames, therefore displays usually operate at a frame rate of more than 25 frames/second. If the frame rate is lower than 25 frames/second, user will see flickering images when viewing contiguous images. 
     In the current digital display systems, the frame rate is usually higher than 50 frames/second. In fact, a rate of 25 frames/second is enough for users to view contiguous images. Therefore this nature characteristic of human eyes can be used to develop an image size adjusting device which provides preferred viewing quality without using the line buffers. The Line buffer is used to maintain a series of image rows to perform high level real time vertical image adjustment. However, since some SRAMs (Static Random Access Memory) are required to maintain each row of pixels in LCD arrays, therefore the line buffer usually takes the cost of occupying a portion of silicon area. In order to save the memory space used by the line buffers, a known simple line-duplicate or line-drop technology is used to adjust (enlarge or reduce) image vertical size. However, such known technology may result in low image quality. 
       FIG. 1  schematically illustrates a known digital camera capturing system. Under image capture mode, the reflection light from a subject travels through a lens module  10 , and the image sensor  11  converts the reflection into electronic image signals to depict the image of the subject. An image signal processor  12  receives and saves the electronic image signals into DRAM (Dynamic Random Access Memory)  13 . In addition, the image signal processor  12  can also process the electronic image signals depending on the system requirement, and the processed electronic image signals are saved in memory  14 . Before the digital camera captures image, a display panel  15  is used to preview the image of the subject. After digital camera captured and saved the electronic image signals in DRAM  13 , digital camera can switch from capture mode to play mode to view the captured image of the subject. Under the play mode, the electronic image signals stored in DRAM  13  can be read out by an image signal processor  12  which enlarges or reduces the image size to fit in the size of display panel  15 . 
     More specifically, since the size of original image depicted by the electronic image signals is not necessary the same size with the display panel  15 , therefore the electronic image signals need to be processed to adjust the size of the original image. If the size of the original image is larger than the size of the display panel  15 , then the size of the original image need to be reduced. When the image signal processor  12  adjusts the image vertical size bases on the known simple line-duplicate or line drop technology, an image distortion may occur. 
     For example, with reference to  FIG. 2   a  and  FIG. 2   b , the original image  20  in  FIG. 2   a  is reduced by half to form the image  21  in  FIG. 2   b . It can be seen from  FIG. 2   a  and  FIG. 2   b , a portion of the image rows of the original image  20  are ignored and the characteristic of which doesn&#39;t show on image  21 , especially for the characteristic of the upper half. Similarly, in  FIG. 3   a  and  FIG. 3   b , the original image  30  of  FIG. 3   a  is reduced by half to form the image  31  in  FIG. 3   b . It can be seen from  FIG. 3   a  and  FIG. 3   b , a portion of image rows of the original image  30  was omitted. As a result, comparing with the original image  30 , image  31  was totally distorted. Next with reference to  FIG. 4   a  and  FIG. 4   b , the original image  40  is enlarged by one and half times (3/2 times) to form the image  41  in  FIG. 4   b . It can be seen from  FIG. 4   a  and  FIG. 4   b , a portion of image rows of original image  40  was duplicated and a serrated edge was resulted. 
     Therefore the present invention provides an image display method which provides a resized image with preferred viewing quality through controlling image rows selection without using line buffer. 
     SUMMARY OF THE INVENTION 
     The present invention provides an image display method suitable for use on a display apparatus having a plurality of contiguous frame periods. And the display apparatus displays an output image during each frame period. The image display method comprises: receiving an original image, wherein the original image has M number of contiguous image rows; grouping a predetermined number of frame periods into an image group; selecting one of M number of image rows in each image frame period as an initial image row, wherein in each of image frame group, a different initial parameter is added to at least two image frames to correspond to different image contents; and in each image group, starting from the initial image row, selecting N number of image rows from M number of image rows according to an image selecting rule to form the output images. 
     The present invention further provides an image display method for use on a display apparatus. The display apparatus has a plurality of contiguous frame periods. And the display apparatus outputs an image during each frame period. The display method includes: receiving an original image comprising M number of contiguous image rows; determining whether the display panel is in the 2q th  or the (2q+1) th  frame period, wherein 0≦q; selecting one of M number of image rows as a first initial image row when the display panel is during the 2q th  frame period, and starting from the first initial image row, selecting N number of image rows from M number of image rows according to an image row selecting rule to form the output image; and adding different initial parameters when the display panel is in the (2q+1) th  frame period; and selecting one of M number of image rows as a second initial image row, and starting from the second initial image row, selecting N number of image rows from M number of image rows according to the image row selecting rule to form the output image. 
     The present invention provides a display apparatus including a receiving device, a display panel and a processing device. The receiving device receives an original image comprising M number of image rows. The display panel has a plurality of contiguous frame periods. And during each frame period, the display panel displays an output image according to the original image. The processing device is connected to the receiving device to group a predetermined number of frame periods into a frame group. During each frame period, the processing device selects one of M number of image rows as an initial image row. And starting from this initial image row, N number of image rows are selected from M number of image rows according to an image row selecting rule to form the output image. Wherein in every frame group, different initial parameter is added to at least two frame periods to correspond to different image contents. 
     In order to the make the aforementioned and other objects, features and advantages of the present invention comprehensible, a preferred embodiment accompanied with figures is described in detail below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  schematically illustrates the known digital camera photography system. 
         FIG. 2   a  and  FIG. 2   b  schematically illustrate an example of image distortion phenomenon when reducing the size of the original image. 
         FIG. 3   a  and  FIG. 3   b  schematically illustrate an example of image distortion phenomenon when reducing the size of the original image. 
         FIG. 4   a  and  FIG. 4   b  schematically illustrate another example of image distortion phenomenon when enlarging the original image. 
         FIG. 5  schematically illustrates a display apparatus according to an embodiment of the present invention. 
         FIG. 6   a  to  FIG. 6   d  schematically illustrates an example of reducing the size of an original image according to an embodiment of the present invention. 
         FIG. 7   a  to  FIG. 7   d  schematically illustrates another example of reducing the size of an original image according to an embodiment of the present invention. 
         FIG. 8   a  to  FIG. 8   d  schematically illustrates an example of enlarging the size of an original image according to an embodiment of the present invention. 
         FIG. 9  is a schematic flow chart of an image display method according to an embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
       FIG. 5  schematically illustrates a display apparatus according to an embodiment of the present invention. With reference to  FIG. 5 , the display apparatus  5  has a receiving device  50 , a processing device  51  and a display panel  52 . The receiving device  50  receives the original image imported from outside or captured by self of the receiving device  50 . In the present embodiment, suppose that the original image includes M number of contiguous image rows. The processing device  51  is coupled to the receiving device  50 . The display panel  52  has a plurality of contiguous frame periods to display contiguous images. And the display panel  52  displays an output image during each frame period according to the original image. In the present embodiment, suppose that the output image is composed of N number of image rows. The processing device  51  groups a predetermined number of frame periods into a frame group. And during each frame period, one of M number of image rows is selected as an initial image row, and starting from the initial image row, N numbers of image rows are selected from M number of image rows according to the predetermined image row selecting rule to form an output image. When the original image size has to be reduced, i.e. when N&lt;M, the processing device  51  ignores a portion of M number of image rows. When the original image size has to be enlarged, i.e. when N&gt;M, the processing device  51  repeatedly selecting a portion of M number of image rows. 
     Here please note, in each frame group, different initial parameters are added to at least two frame periods so as to correspond to different image contents. In other words, in each frame group, the output images from at least two frame periods are different. Therefore, when reducing (M&gt;N) or when enlarging (M&lt;N) the size of original image, a plurality of output images are switched during a plurality of contiguous frame periods, with the help of persistence of vision in human vision system, viewer sees a plurality of overlapped output images, therefore user sees less image distortion. 
     In the following descriptions, for example the processing device  51  groups every two contiguous frame periods into a frame group. The original image is represented with L(m), wherein 0≦m≦M−1, for example L(0) represents the first image row of the original image. The output image is represented with L′(n,t), 0≦n≦N−1, and t is a time parameter. The relation between M and N is described by the below formula:
 
 N =int[( M− 1)* s]+ 1
 
     Wherein int[ ] means integers are retained, s is a adjustment parameter. When the adjustment parameter s&gt;1, means to enlarge the size of the original image; on the contrary, if s&lt;1, means to reduce the size of the original image. Therefore it is known that the original image has M number of image rows, and after the original image is enlarged or reduced, the output image will then have N number of image rows. The inverse (1/s) of the adjustment parameter s is the selection interval. 
     The relation (i.e. image row selection rule) between the original image L(m) and output image L′(n,t) is described below:
 
 L ′( n,t )= L (int[ n/s +α( t )+ρ])  Formula 1
 
     Wherein α(t) represents the initial image row selected according to the frame period, ρ represents a row selecting parameter. In the present embodiment, when ρ=0.5, it means rounding rule is applied; when ρ=0, means unconditional discard rule is applied. 
     Since the output images are displayed and updated under separated time-domain (for example t=0, T, 2T . . . ), therefore formula 1 is revised as:
 
 L ′( n,kT )= L (int[ n/s +α( k )+ρ])  Formula 2
 
     Wherein T represents a frame period, and k is an integer. α(k) is divided into α(2q) and α(2q+1) which respectively represents the initial image row selected by the 2q th  frame period and the initial image row selected by the (2q+1) th  frame period, wherein 0≦q. 
     With reference to  FIG. 6   a  to  FIG. 6   c , suppose that M=16, N=8, s=½, α(2q)=0, α(2q+1)=1, and ρ=0.5. Wherein α(2q)=0 represents that during the 2q th  frame period the first image row (1 st ) of the original image is selected as the initial image row. And α(2q+1)=1 represents that during the (2q+1) th  frame period the second image row (2 nd ) of the original image is selected as the initial image row. In other word, the output image of the 2q th  frame period and the output image of the (2q+1) th  frame period have different parameter α, i.e. the 2q th  frame period and the (2q+1) th  frame period correspond to different initial frame rows. Since adjustment parameter s=½, means the original image will be reduced by ½. In other word, starting from the initial image row, in every two rows (1/s=2), the image row of the original image is selected once as the image row of the output image.  FIG. 6   b  schematically illustrates the output image displayed during the 2q th  frame period.  FIG. 6   c  schematically illustrates the output image displayed during the (2q+1) th  frame period. With a switched parameter α, and together with the persistence of vision of human vision system, the output images of the 2q th  and the (2q+1) th  frame periods are mixed, user will see the image shown in  FIG. 6   d . Comparing with the image in  FIG. 2   b , the image shown in  FIG. 6   d  can better describe the characteristic of the original image, so the image distortion is reduced. 
     Similarly, with reference to the images in  FIG. 7   a  to  FIG. 7   c , suppose that M=16, N=8, s=½, α(2q)=0, α(2q+1)=1, and ρ=0.5.  FIG. 7   b  schematically illustrates the output image displayed during the 2q th  frame period;  FIG. 7   c  schematically illustrates the output image displayed during the (2q+1) th  frame period. With the switching parameter α, and together with the persistence of vision of human vision system, the output images of the 2q th  and the (2q+1) th  frame periods are mixed, then user will see the image shown in  FIG. 7   d . Comparing with the image in  FIG. 3   b , the image shown in  FIG. 7   d  can better describe the complete original image, so the image distortion is reduced. 
     It is know from the embodiments of  FIG. 6   a - 6   d  and  FIG. 7   a - 7   d , when reducing the size of the original image, α(2q+1) is set to 1/(2s). 
     Next with reference to  FIG. 8   a  to  FIG. 8   c , suppose that M=8, N=12, s=3/2, α(2q)=0, α(2q+1)=3/2, and ρ=0.5. Wherein α(2q)=0 means that during the 2q th  frame period the first image row (1 st ) of the original image is selected as the initial image row. And α(2q+1)=3/2 means that the selected result during the (2q+1) th  frame period is between the first (1 st ) image row and the second image row (2 nd ) of the original image. Since ρ=0.5 means rounding rule is applied, therefore the second (2 nd ) image row of the original image is selected as the initial image row during the (2q+1) th  frame period. Since the adjustment parameter s=3/2, means the original image will be enlarged by 3/2 times. In other word, starting from the initial image row, the image row of the original image is selected once in every 2/3 rows (1/s=2/3) as the image row of the output image. If the selecting result is between the two image rows of the original image, then one of the image rows is selected according to rounding rule.  FIG. 8   b  schematically illustrates the output image displayed during the 2q th  frame period.  FIG. 8   c  schematically illustrates the output image displayed during the (2q+1) th  frame period. With the switching parameter α, and together with the persistence of vision of human vision system, the output images of the 2q th  and the (2q+1) th  frame periods are mixed, user will see the image shown in  FIG. 8   d . Comparing with the image in  FIG. 4   b , the image shown in  FIG. 8   d  is smoother, the image distortion is reduced. 
     It is known according to the embodiment of  FIG. 8   a - 8   d , to enlarge the original image, α(2q+1) is set to 1/s. 
       FIG. 9  shows a flow chart of an image display method according to an embodiment of the present invention. This flow chart is suitable for a display apparatus. In the embodiment, for example every two contiguous frame periods are grouped into a frame group. α(2q) is represented with C0, α(2q+1) is represented with C1, and an initial parameter Cini is set. An enlargement parameter Cu and a reduction parameter Cd are set, wherein Cu=1/s, and Cd=1/2s. In addition, parameters Ki and Ko are further set, wherein 0≦Ki≦M−1, and 0≦Ko≦N−1. Wherein the parameter Ki tells which image row of the original image is currently selected, and the parameter Ko shows which number of the image row of the output image is. For example, when Ki=0, means the first (1 st ) image row of the original image is currently selected, and so on. When Ko=0, means the first image row of the output image, and so on. In the embodiment of  FIG. 9 , parameter A(n) is set, 0≦n=≦N−1. The row selection parameter is set to 0.5, means the rounding rule is applied. 
     First, in step S 900 , the initial image row selected in the 2q th  frame period is initialized as the first image row (C0=Cini) of the original image. Parameter n is initialized to 0 (n=0), and parameter Ki and Ko is initialized to 0 (Ki=0, Ko=0). It is determined in step S 901  that whether the original image is to be enlarged. If yes, then set the parameter C1 to the enlargement parameter Cu (C1=Cu) (step S 902 ); if not, then set the parameter C1 to the size reduction parameter Cd (C1=Cd) (step S 903 ). Next, determine if the display apparatus is during even number frame period (step S 904 ). If yes, then set the parameter A(n) to C0 (A(n)=C0) (Step S 905 ); if not, then set parameter A(n) to C1(A(n)=C1) (step S 906 ). Step S 907  calculates currently which number image row (Ki=Ki+INT[A(n)]) of the original image should be selected, and calculates the fraction portion (A(n)=A(n)−INT[A(n)])) of parameter A(n), to determine if the fraction portion of A(n) is greater or equal to 0.5 (A(n)&gt;=0.5) (step S 908 ). If the fraction portion of A(n) is greater or equal to 0.5, then the next row (Ki=Ki+1) of the image row acquired through calculation in step S 907  is selected (step S 909 ). If the fraction portion of the parameter A(n) is less than 0.5, then go to step S 910 . 
     After determining to select the image row of the original image, the selected image row of the original image are converted to form the image row (L′(Ko)=L(Ki)) of the output image, (step S 910 ). In step S 910 , the parameter A(n) (A(n+1)=A(n)+1/s, n=n+1) of the next image row of the output image is set. Next determine if the image row (Ko) of the formed output image is the last row (step S 911 ). If yes, then finish forming the output image of the frame period (step S 912 ); if not, then proceed to form the image row of the next output image (Ko=Ko+1) (step S 913 ). Then repeat step S 907 -S 913 . 
     According to the embodiment of  FIG. 9 , different output images are produced during the 2q th  and the (2q+1) th  frame periods. The output images formed during the 2q th  and the (2q+1) th  frame periods are mixed according to persistence vision of human vision system, user will see the mix of different images, therefore the enlarged or reduced image is more smooth, the distortion is reduced. In addition, according to the embodiment of the present invention, since the line buffer is not necessary to use when enlarge or reduce the image size, therefore the size and the cost of the display apparatus are reduced. 
     While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims. 
     Description of the Main Components 
       10 ˜lens module;  11 ˜image sensor;  12 ˜image signal processor;  13 ˜DRAM;  14 ˜memory;  15 ˜display panel; 
       5 ˜display apparatus;  50 ˜receiving device;  51 ˜processing device;  52 ˜display panel;