GB2459475A

GB2459475A - Transmitting and receiving a still image

Info

Publication number: GB2459475A
Application number: GB0807403A
Authority: GB
Inventors: Owain Huw Rees
Original assignee: EMBEDOLOGY Ltd
Current assignee: EMBEDOLOGY Ltd
Priority date: 2008-04-23
Filing date: 2008-04-23
Publication date: 2009-10-28
Anticipated expiration: 2028-04-23
Also published as: GB0807403D0; GB2459475B

Abstract

In a method for transmitting and receiving an image for display by a thin client, a parameter of a formatted image signal is used either as an indicator as to whether or not the image signal should be displayed by the thin client (1 in fig.1) receiving the signal, and/or as an indicator of the position in which the image signal is to be displayed as part of a composite display of multiple image signals by the thin client. The parameter may dictate that an image is not to be displayed when this represents no change over a preceding image signal, and this image signal may be reduced in size before sending by a web server (2 in fig.1). Simulated moving images can therefore be generated with lower latency and bandwidth. The parameter may comprise height and width image properties.

Description

Method and Means for Transmitting and Receiving an Imjge This invention relates to a method and means for transmitting and receiving an image for display by a thin client.

A thin client by definition has limited ability to display moving images. One example of a thin client is the world wide web browser (web browser). Web browsers can display moving images of certain formats when they are equipped with additional software modules, commonly known as plug-ins. The term "thin client" is used herein to mean a client program that initiates requests to a server and displays the information that the server returns.

A web browser has the ability to display still images encoded in formats supported by it.

Still image encoding formats commonly supported by web browsers include PNG, GIIF and JPEG. These still images can be transported to the web browser by a number of transport protocols, most commonly but not exclusively the Hypertext Transfer Protocol (HTTP) and the Secure Hypertext Transfer Protocol (HTTPS).

A web browser can give the illusion of displaying a moving image by showing a rapid succession of still images. Each still picture frame (or part frame) has to be sent and displayed in its entirety. The individual still images are loaded and displayed by a web browser run-time environment. One example of such a run-time environment is o * *** ECMAscript (commonly known as Javascript).

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* The problem with showing a rapid succession of still images in a thin client is that each still picture frame (or part frame) has to be sent and displayed. Even when there is no *: : motion or change, it remains necessary to keep sending frames. I. S * IS * S.

Also, some still image encoding formats, such as GIF and PNG are able to support simple animation effects within the file format, without relying on the run-time environment of the browser.

An example is shown in Figure 1 comprising a thin client 1, in this case a web browser, receiving images from a source 2, in this case a web server over the internet 3.

Figure 2 shows a timeline diagram of the transmission of the still images between the server 2 and thin client 1 in Figure 1.

In step 1, the client requests whether there has been a change to the moving image frame or part frames.

In step 2, the server responds that there has been a change, and that the thin client should request an image update.

In step 3, the thin client requests the full or part frame image.

In step 4, the server delivers the full or part frame to the thin client.

Note that it is necessary to deliver the moving image in the least time possible. The largest contributor to communications latency is the time taken transporting the image over the communications medium, in this case the internet 3. This is shown as time interval t' in Figure 2. This scheme takes 4t time intervals for one image update. The HTTP protocol as applied to web browser communications means that all image requests are instigated from the browser. The server cannot inform the browser that a new image is available. *... * S * ***

Therefore, only the necessary images are sent to the thin client. However, since each S...

update has to be requested in a two stage process, the overall delay is 4t. *

Summary of the Invention * **

According to the invention, a parameter of a formatted image signal is used either as an * indicator as to whether or not the image signal should be displayed by a thin client receiving the signal, andlor as an indicator of the position in which the image signal is to be displayed as part of a composite display of multiple image signals by the thin client.

The invention addresses the need to keep sending image signals, but allows selected image signals to be encoded using said parameter so as to direct the run time in the thin client environment to make a decision whether and how a received image signal should be displayed as a part, or whole of, the displayed image.

Brief description of the drawing

Figure 1 is an example of the components of a prior art web browser/web server system; Figure 2 is an example of the timelines involved in operation of the system of Figurel; Figure 3 is a flow chart of a first embodiment of the invention; Figure 4 is an example of the timelines involved in operation of the first embodiment of the invention; Figure 5 is an example of a tile configuration used in a second embodiment of the invention; and Figure 6 is a flow chart of the second embodiment of the invention.

Disclosure of the Invention

The first embodiment has the same physical configuration as that shown in figure 1. A thin client 1, in this case a web browser, draws a series of still images from a remote web server 2 to give the illusion of a moving picture over a communications medium, in this case the internet 3. The web browser can display images and supports an ECMAscript run-time environment. * **

ECMAscript supports an image signal format which allows programmatic access to the * images contained in the HTML document displayed by the browser. Image parameters defined in the format can be accessed and allow limited manipulation of the images. For **** * * example, one image can be replaced by another image under programmatic control. * **

Two image parameters that can be accessed within ECMAscript are the height and width of *.: an image loaded into the web browser's memory. This embodiment of the invention uses the height andlor width of the image as the image parameter to decide whether an image retrieved from the server should be displayed and/or where it should be displayed.

A flow chart of the encoding and subsequent decoding process is shown in Figure 3.

The image encoding loop, shown on the left, captures a target image signal and calculates a hash value. If the hash value has changed from the hash value of a preceding captured image signal, the new image signal is sent in said format with the standard parameter setting to the receiving web browser for it to be processed and displayed in the usual way.

However, if there is no change in the hash value of the captured image signal, a modified image signal is sent to the receiving web browser with said parameter set to indicate that it should not be processed for display.

The ideal modified image signal should be as few bytes as possible, because it represents an idle "no image update" instruction from the server. A typical modified image signal may comprise a single pixel with height and width parameter lxi. Thus, when the encoding process is monitoring a target image which is not changing, a continuous stream of modified image signals, each comprising a single pixel, is returned to the browser. This reduces the bandwidth requirement to transmit the image.

The receiving browser is requesting images from the server at a regular interval. As each image signal is received, the run time environment displays each image in the web browser, unless the received image signal has a parameter setting of height and width lxi indicating "no image update", in which case, this image signal is ignored. The receiving browser then requests another image from the server, and the process continues. * *

A timeline diagram for this embodiment is shown in Figure 4. This should be compared to * the timeline of the prior art described in Figure 2. Since the decision whether to show each received image is taken by the web browser, a frame only requires one request period and * one response period rather than two. Therefore, this method takes 2t time intervals for one image update rather than 4t time intervals as used in the known method of Figure 2.

: There is an enhancement to this embodiment, where some previous hash values are retained and the hash value of the latest image is compared with the several preceding values. If there is a match between current and preceding hash values, a modified image signal is sent to the receiving web browser with the parameter set to indicate "no image update" Thus this embodiment can accommodate target images that change slightly on a periodic basis e.g. a flashing cursor.

Another feature of the invention involves using different size image tiles to encode their position within the image to be displayed.

Figure 5 shows how a target image can be divided such that each tile has a size peculiar to its position. Therefore the size parameters of height and width in the image signal format can be used to encode the position of the tile in the display and detected by the web browser to decide where to display the tile in the display. The relationship between image dimensions and its position can either be a formulaic relationship or based on a lookup table shared between the web browser and server.

A flow chart of the encoding and decoding process for this embodiment of the invention is shown in Figure 6.

The image-encoding loop captures the target image and divides the image as per the tiled arrangement described above. A hash value is calculated for each tile. If the hash value has changed from the preceding capture, the new image tile is sent to the receiving web browser in the usual way encoded by the size parameters according to its position in the display. If there is no change in a captured image tile, an image signal is returned to the receiving web browser with the "no image update" setting.

The receiving browser is requesting images from the server at regular intervals. As each ** image tile is received, the run time environment displays each image in the appropriate display position in the web browser according to the size parameters, unless the received * image meets the test of being a "no image update" image signal, in which case, the image signal is ignored. The receiving browser then requests another image from the server, and * * the process continues.

Although an embodiment of the invention has been described above in which the size dimensions of the image signal are used to indicate both changes to, and position of an image or tile, it will be appreciated that these two indicators can be used separately and the size dimension used solely (either height or width or both) to indicate whether or not an image signal is to be displayed, or the height and width of the size dimension used to indicate the position of a tile. * ** * S S * .* **** * S 55S S... S.. * ** * . S * .. * S.

Claims

Claims 1. A method of displaying an image under the control of a thin client in which an image signal is received by the thin client in a still image format with an image parameter set by the sender of the image to indicate whether or not it is to be displayed by the thin client, the thin client reading said parameter and deciding accordingly whether or not to process the image signal and display the image.
2. A method as claimed in claim 1 in which the thin client receives a sequence of image signals and reads the image parameter of each to decide whether or not it should be displayed, thereby to generate a displayed image which changes with changes in the still images received without having to process images signals deemed by the sender not to represent a change.
3. A method as claimed in claim 1 or 2 in which said image parameter is further set by the sender to indicate a position in which the image should be displayed in a composite display by the thin client, the thin client reading said parameter and deciding accordingly where to display the image, if it is to be displayed.
4. A method of transmitting an image for display under the control of a thin client, in which an image signal is transmitted in a still image format with a parameter set to indicate whether or not the image signal should be processed and the image displayed by .. the thin client. * ** * ***
5. A method as claimed in claim 4 in which a sequence of image signals is * : * transmitted to the thin client and the image parameter of each is set according to whether or S...*:. not the associated still image has changed in some way compared with a preceding still image so that the display changes with changes in the received images without the thin ::; client necessarily having to display all transmitted image signals.
6. A method as claimed in claim 5 in which one still image and a preceding still image are compared by generating a hash from each and comparing these hashes, and the level of change used to set the image parameter of said one image signal.
7. A method as claimed in claim 4 or 5 in which said image parameter is further set to indicate a position in which the associated image is to be displayed by the thin client in a composite display, if it is to be displayed.
8. A method as claimed in claim 3 or 7 in which said image parameter is related to the position of the image by a predetermined formula or look-up table.
9. A method of displaying an image under the control of a thin client in which an image signal is received by the thin client having a still image format and image parameter which is set by the sender to indicate a position in which it is to be displayed in a composite display, the thin client reading said parameter and deciding accordingly where to display the image in the display.
10. A method of transmitting an image for display in a composite display under the control of a thin client, in which an image signal is transmitted in a still image fonnat with an image parameter set to indicate a position in which the image is to be displayed by the thin client in the composite display.
11. A method as claimed in claim 9 or 10 in which a sequence of image signals are transmitted and are received by the thin client, thereby to produce an image which changes with changes in the images.
12. A method as claimed in claim 2 or 5 or 11 in which the sequence of image signals *:*::* represent a moving image which is displayed under the control of the thin client. * *
13. A method as claimed in any one of the preceding claims in which the images are * transmitted to the thin client using the HTTP or HTTPS or FTP protocol. **.
14. A method as claimed in any one of the preceding claims in which the image ** format comprises GIF or JPEG or PNG or SVG or BMP still image format. ** 0

* *:
15. A method as claimed in any one of the preceding claims in which the thin client comprises a web browser.
16. A method as claimed in any one of the preceding claims in which the sender of the image comprises a web browser.
17. A method as claimed in any one of the preceding claims in which the thin client contains a run time environment capable of running a computer program or script.
18. A method as claimed in any one of the preceding claims in which receipt of an image by the thin client is acknowledged to the sender by sending an acknowledgment that incorporates the image parameter of the received image signal.
19. A method as claimed in any one of the preceding claims in which the image parameter comprises one or more of the dimensions of the image which is set by changing one or more dimensions of the image.
20. A method as claimed in claim 19 in which said dimensions comprise the width and height parameters specified in ECMAScript.
21. A method as claimed in claim 20 in which one or both the width and height dimensions are reduced to indicate that the image is not to be displayed.
22. A computer product adapted to carry out the method of any one of the preceding claims.
23. A method of displaying an image substantially as herein described with reference to the accompanying drawings.
24. A method of transmitting an image substantially as herein described with reference to the accompanying drawings. *... * * * S.. *.. *S *.*S S *S * . S * S. IS *S SS * *5