Computer graphics processing and selective visual display system – Computer graphics display memory system – Graphic display memory controller
Reexamination Certificate
2001-04-04
2004-06-08
Bella, Matthew C. (Department: 2671)
Computer graphics processing and selective visual display system
Computer graphics display memory system
Graphic display memory controller
C348S567000, C348S571000, C382S254000
Reexamination Certificate
active
06747656
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image processing apparatus performing for example asynchronous input/output type digital image processing using an image memory and a method of the same, and a display apparatus using the image processing apparatus.
2. Description of the Related Art
In asynchronous input/output type digital image processing using a image memory, a write operation of image data into the image memory and a read operation of image data from the image memory are performed independently. For this reason, sometimes input frames are switched in the middle of image output.
In general, in the case of a still image having a high correlation between frames such as with graphics, this switching cannot be discerned so does not become a problem.
In the case of a moving image, however, this creates a horizontal stripe which constitutes noise moving on the screen. This memory overrun is referred to as “field tearing”.
Conventionally, as a method of avoiding this field tearing (memory overrun), mainly a “double buffer method” of using a plurality of image memories and storing the image data in a different memory for every frame and an “output line delay method” of adjusting read and write timings of the input/output images with respect to a single image memory have been employed.
Summarizing the problem to be solved by the invention, generally, when processing a moving image, however, use is made of a vertical synchronization method of locking a phase of an output side vertical synchronization signal V-SYNC with the input, so the problem of the field tearing can be solved by the “double buffer method” of processing the input signal in a different memory for every field (or frame).
This “double buffer method”, however, requires a large capacity memory, so there is a disadvantage of an increased cost.
The “output line delay method” is free from any cost disadvantage and is a general function available in almost all scan converters at present.
This conventional “output line delay method”, however, has the disadvantage that it is difficult to avoid field tearing under all conditions with a fixed amount of delay since the required delay differs according to the frequencies of the input and output signals and degree of a special image processing such as enlargement or reduction of the image.
Also, field tearing becomes noise discernable only with respect to the moving image portion, therefore it was not practical to have the user adjust the number of delay lines.
Below, an explanation will be given, with reference to the drawings, of the reason why memory overrun is fixed on a screen in the vertical synchronization mode in the “output line delay method” for the case of enlargement and reduction.
First, an explanation will be given of the case of enlargement with reference to
FIG. 12
to FIG.
16
.
FIG. 12
is a view of an image write area and read area of a frame memory in a case where an image is enlarged 2-fold in the vertical synchronization mode at the time of input of a still image.
In
FIG. 12
, reference numeral
1
denotes a frame memory, ARWR an image write area, and ARRD a read area.
As will be understood from
FIG. 12
, the memory area ARRD accessed on the read side is a half of the memory area ARWR accessed on the write side.
Also, because of the vertical synchronization mode, the times required for the write and read operations of the image in 1V (1 vertical synchronization period) are the same, so a write speed of the image becomes two times the read speed.
The vertical synchronization signals V-SYNC serving as the triggers for starting the write and read operations are identical in terms of time, but the positions for starting the access differ (concretely, in
FIG. 12
, a write start position is (a) and a read start position is (b)), therefore, right after the start of access, the already written information of one frame before is read and written (in
FIG. 12
, a write end position is (c) and a read end position is (d)), then the information of the current frame is read.
Next, an explanation will be given of the principle of the occurrence of field tearing at the time of enlargement with reference to moving image samples shown in FIG.
13
.
FIG. 14
is a view of the transition over time of the image data inside a frame memory and output images in a case where two consecutive frames having different image information as shown in
FIG. 13
are processed in the vertical synchronization mode.
In
FIG. 14
, the center portion of the image is cut out, so the memory positions of the write and read operation match at the center of the screen. The timings of the read and write operations become reversed at this position. The field tearing from an old image to a current image occurs there.
Even when changing the enlargement rate, the relationship of “write area>read area” is held, so the field tearing always occurs at the screen center due to a similar reason.
FIG. 15
is a view of the transition over time of the image data inside the frame memory and the output images in a case where an image is shifted downward.
When shifting the image phase, the situation differs according to the amount and direction of movement.
The downward shift of the image means to take out an upper portion data of the memory.
In this case, the positions of the memory for starting access match, in other words, since the write operation and the read operation start from the identical line and the write speed is two times of the read speed, overrun does not occur or field tearing is caused at the uppermost portion of the screen, generally, a blanking area.
Also,
FIG. 16
is a view of the transition over time of the image data inside the frame memory and the output images in a case where an image is shifted upward.
As shown in
FIG. 16
, when shifting an image upward, the positions of the memory where the accesses end match, in other words, the write and read operations end on the same line, so the field tearing will occur in the lowermost portion of the screen or the field tearing will not occur.
As will be understood from the above description, the position of occurrence of field tearing varies according to the enlargement rate and the amount of shift. Depending on the amount of the shift, there are also cases where the field tearing is hidden in the blanking area, but in principle the field tearing always occurs.
First, an explanation will be given of the case of reduction with reference to
FIG. 17
to FIG.
21
.
FIG. 17
is a view of the image write area and read area of a frame memory in a case where an image is reduced to ½ (image center reduction) in the vertical synchronization mode at the time of input of a still image.
In this case, the memory areas accessed on the read side and the write side are identical.
Because of the vertical synchronization mode, the vertical synchronization signals V-SYNC serving as the triggers for starting the write and read operations are identical in terms of time, but the times for starting access differ (in
FIG. 17
, the write start position is (a) and the read start position is (b)).
In the period immediately after the start of access and up to the read start position (b), the memory is not accessed for a read operation. Only the lines are counted, and blanking is applied to the screen.
At the point of time of the read start position (b), the image of the current frame has been already written up to ¼ of the entire image, so the image taken out at the time of the start of the read operation of the memory is the data of the current frame.
On the other hand, at the end of the read operation (indicated by (d) in FIG.
17
), irrespective of the end line of the memory being read, the write side has finished only ¾ of the entire image, so the data of the previous frame ends up being read at the lower portion of the screen.
Below, an explanation will be given of the principle of field tearing by using the moving image samples shown in
FIG. 18
in the same way as the time of enlargement
Bella Matthew C.
Maioli Jay H.
Monestime Mackly
LandOfFree
Image processing apparatus and method of the same, and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Image processing apparatus and method of the same, and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Image processing apparatus and method of the same, and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3365395