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Definition

'Screen content' is a term for images showing content that can be seen on computer screens during typical office work. This term is mainly used by the vidio compression community.

Example of a natural image taken by a camera

Unlike video data captured by video cameras, computer screens usually display text and graphics combined with pictorial elements. Text and graphics are also referred to as 'computer-generated', 'born-digital', or 'synthetic', while pictorial elements such as photographs or medical images (e.g. X-ray images) are called 'natural'. Note that computers can generate photorealistic images that appear natural. A former term for images that contain a mixture of synthetic and natural elements was 'compound images'^[1].

Synthetic data is characterised by a small number of different colours and repetitive patterns. Natural images usually do not contain sharp colour or intensity edges but varying colour gradients. This is mostly combined with a certain amount of noisy texture.

Dealing with screen content

Applications dedicated to screen content

Main applications for processing screen content data include web-based application sharing and desktop sharing. Other keywords are 'virtualized desktop' or 'thin client'. The idea behind this is the 1:1 transfer of screen content from a computer to a remote display.^[2]^[3].

Compression of screen content

The Video Electronics Standards Association (VESA) undertakes activities on display stream compression (DSC)^[2]. The latest standard for video compression, High Efficiency Video Coding (HEVC)^[4]^[5], contains several tools for the treatment of synthetic image content which are summarised as 'screen content coding' (SCC). There are some academic-driven efforts to improve the compression of screen content as, for example, towards its efficient lossless compression^[6].

Quality assessment

The quality assessment of screen content ^[7] has high importance because the digital modification of synthetic image data (e.g. by lossy compression) leads to higher visual degradation than the modification of pure natural image data. Dedicated compression schemes must take the human visual system into account and should try to get a good compromise between high compression ratios and low quality degradation.

References

^ Mogi, T.: A hybrid compression method based on region separation for synthetic and natural compound images. Proceedings 1999 International Conference on Image Processing (Cat. 99CH36348), Kobe, Japan, 24-28 Oct. 1999
^ ^a ^b Frederick G. Walls and Alexander Sandy MacInnis: VESA display stream compression: An overview, SID International Symposium, Digest of Technical Papers, San Diego, CA, Vol.45, No.1, 2014, pp.360-363
^ Pan, Z., Shen, H., Lu, Y., Li, S., Yu, N.: A low-complexity screen compression scheme for interactive screen sharing. IEEE Transactions on Circuits and Systems for Video Technology, Vol.23, No.6, June 2013
^ ITU-T H.265 / ISO/IEC 23008-2 HEVC: High efficiency video coding, recommendation, April 2013
^ Xu, J.; Joshi, R.; Cohen, R.R.: Overview of the Emerging HEVC Screen Content Coding Extension. IEEE Trans. on Circuit and Systems in Video Technology, Vol.26, No.1, Jan. 2016, 50-92
^ Strutz, T.: Lossless Intra Compression of Screen Content based on Soft Context Formation. IEEE Journal on Emerging and Selected Topics in Circuits and Systems -- Screen Content Video Coding and Applications, Vol.6, No.4, 2016, 508-516
^ Ke Gu, Shiqi Wang, Huan Yang, Weisi Lin, Guangtao Zhai, Xiaokang Yang, and Wenjun Zhang: Saliency-Guided Quality Assessment of Screen Content Images, IEEE Transactions on Multimedia, Vol.18, No.6, 2016, pp.1098 - 1109

[1] Mogi, T.: A hybrid compression method based on region separation for synthetic and natural compound images. Proceedings 1999 International Conference on Image Processing (Cat. 99CH36348), Kobe, Japan, 24-28 Oct. 1999

[VESA-2] Frederick G. Walls and Alexander Sandy MacInnis: VESA display stream compression: An overview, SID International Symposium, Digest of Technical Papers, San Diego, CA, Vol.45, No.1, 2014, pp.360-363

[3] Pan, Z., Shen, H., Lu, Y., Li, S., Yu, N.: A low-complexity screen compression scheme for interactive screen sharing. IEEE Transactions on Circuits and Systems for Video Technology, Vol.23, No.6, June 2013

[4] ITU-T H.265 / ISO/IEC 23008-2 HEVC: High efficiency video coding, recommendation, April 2013

[5] Xu, J.; Joshi, R.; Cohen, R.R.: Overview of the Emerging HEVC Screen Content Coding Extension. IEEE Trans. on Circuit and Systems in Video Technology, Vol.26, No.1, Jan. 2016, 50-92

[6] Strutz, T.: Lossless Intra Compression of Screen Content based on Soft Context Formation. IEEE Journal on Emerging and Selected Topics in Circuits and Systems -- Screen Content Video Coding and Applications, Vol.6, No.4, 2016, 508-516

[7] Ke Gu, Shiqi Wang, Huan Yang, Weisi Lin, Guangtao Zhai, Xiaokang Yang, and Wenjun Zhang: Saliency-Guided Quality Assessment of Screen Content Images, IEEE Transactions on Multimedia, Vol.18, No.6, 2016, pp.1098 - 1109

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