Factoring a mobile client's effective processing speed into the image transcoding decision

Richard Han*

*Corresponding author for this work

Research output: Chapter in Book/Report/Conference proceedingConference proceeding contributionpeer-review

7 Citations (Scopus)

Abstract

An image transcoding proxy decides whether to transcode an image fetched from the Web based either on the criterion of reducing the overall response time (store-and-forward proxies), or the criterion of avoiding buffer overflow (streamed proxies). In this paper, we introduce a new parameter, namely a mobile client's effective processing speed, into the analytical formulation of both transcoding decisions, and study the practical importance of this parameter when transcoding is applied for standard PDA clients. CPU-intensive operations like image decompression, colorspace conversion and scaling can together add excessive delay to the perceived response time when performed on a mobile client that has severely limited processing capability. Under certain conditions, a transcoding proxy that sends GIF or JPEG images can incur greater delay due to decompression on a PDA client than a better informed transcoding proxy that chooses instead to send bit-mapped equivalents that incur little to no client-side decoding delay. We designed three experiments that partitioned image processing functions between a proxy and a standard PDA in order to assess the importance of a client's CPU limitations on the image transcoding decision. First, images were fetched by a standard Web browser that decompressed GIF's on the PDA. This browser also enforced scaling on every image to fit within the PDA's small screen. Second, we added a transcoding proxy that pre-scaled images, thereby bypassing the browser's scaling function but still requiring the browser to decompress the scaled GIF's. Third, we migrated both scaling and decompression off of the PDA on to the proxy. The proxy pre-scaled as before, and also transcoded GIF's to grayscale bitmaps that required no client-side decompression. We measured response times from each of these three experiments and quantified how much improvement in response time can be achieved when a proxy assists a CPU-limited PDA by performing some or all CPU-intensive image processing tasks on the transcoding proxy.

Original languageEnglish
Title of host publicationProceedings of the 2nd ACM International Workshop on Wireless Mobile Multimedia, WOWMOM 1999
Place of PublicationNew York, NY
PublisherAssociation for Computing Machinery, Inc
Pages91-98
Number of pages8
ISBN (Electronic)1581131291, 9781581131291
DOIs
Publication statusPublished - 1999
Externally publishedYes
Event2nd ACM International Workshop on Wireless Mobile Multimedia, WOWMOM 1999 - Seattle, United States
Duration: 20 Aug 1999 → …

Publication series

NameProceedings of the 2nd ACM International Workshop on Wireless Mobile Multimedia, WOWMOM 1999

Conference

Conference2nd ACM International Workshop on Wireless Mobile Multimedia, WOWMOM 1999
CountryUnited States
CitySeattle
Period20/08/99 → …

Keywords

  • CPU
  • Image processing
  • Mobile
  • Partitioning
  • PDA
  • Proxy
  • Transcoding

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