The universe of our color screens
The screens have invaded our daily lives: computers, tablets, televisions, smartphones, we barely communicate anything but through them. We are also becoming increasingly demanding about the quality of their resolution. The transition from the small black-and-white formats of the early 1950s to today's large screens with vivid colors can only be achieved thanks to astonishing progress, both in terms of signal transmission and their compression. Exploiting the peculiarities of our visual system, the JPEG format and its various derivatives deliver images considered sharp while remaining of an acceptable "weight." To achieve this, a transformation inspired by Fourier's work produces excellent results.
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The components of our images: luminance and chrominance
Screens are now part of our daily lives—and taking up more and more space. But how are the images they display constructed? What lies behind the standards (ITU 709, etc.) and formats (4:3, 16:9, etc.) in use?
From the Fourier transform to the discrete cosine transform
How do we go from discrete digital signals to the light and color waves emitted by our screens, and how can we reduce incoming data streams as much as possible without overly degrading the images? Converting signals to a spectral representation allows them to be compressed selectively to suit our visual system.
The JPEG format
By breaking each image into blocks and moving into the frequency domain, the JPEG format discards high frequencies, to which our eyes are less sensitive. This is what makes the compression effective. JPEG: vector spaces underpinning image compression!
Unexpected changes
Requirements for display quality are becoming increasingly stringent. Screens are growing ever wider, and their color gamut continues to expand.
Lena, the "first lady" of the Internet
Nearly every computer scientist knows this image: "Lena" (or "Lenna") is a photograph that has been used as a standard test image for digital image-processing algorithms for almost fifty years.
Tomorrow's ultra-high-definition TV
Our screens are taking up more and more room. And they are not done growing yet. The International Telecommunication Union (ITU) has set a new standard for tomorrow’s televisions: ITU 2020.
Television’s “missing” lines
The information received by our television sets is digital. Each image corresponds to a certain number of bits specifying the luminance and chrominance of each pixel (see the article “The components of our images: luminance and chrominance”). But the on-screen image is not the whole story.