17 February 2009

Dynamic Range

The Online Photographer has posted an excellent article, More on Dynamic Range, on the range of brightness in a scene, how it is captured as a photographic image, how to fit that range into the range of lightness levels recorded by the camera and express that range in the rendered medium, whether a JPEG image viewed on a monitor or a paper print.

He's right that dynamic range is the most abused, misused and poorly understood term in digital photography. It's the only short hand we have for "range of brightness values" or "range of tonal values," which are both going to give your fingers cramps if you write them often enough.

There is a lack of understanding by many photographers about the basic process of recording an image and producing a visible print from it. There are crucial, but precise, distinctions to be made, which took a long time and much expertise to establish in analog photography, so the confusion is not surprising.

The first thing to consider is the range of brightness in the scene (which the Online Photographer article demonstrates and discusses). It may seem obvious to some, but is often counter-intuitive, that a distinction exists between the range of measurable brightness values in the scene (and remember, most are reflected light, but some is direct from light sources or specular reflections, for purposes of exposure, it is good to consider only reflected light and not specular highlights, since they do not contain any detail or information) and the representation of those values as tonal values in the recording medium (in the camera, film or sensor).

The difference between the range of brightness in the scene and the translation of the brightness levels into tonal levels recorded by the camera (density in film, tonal levels in digital) is not immediately obvious, but the camera does not record brightness, but some analog of it, clumps of grain or numbers. To see the picture, the range of tonal levels must be translated back into a range of brightness values. We do this when printing a negative to photographic paper or viewing a transparency film slide through transmitted light (a projector or lightbox).

In the digital realm, the image rendered from raw capture data or printed to paper is the output, which must be translated into reflected or transmitted light so we can view the image. A complication in digital photography is the JPEG image, which places limitations on the original data. It would not matter either, if it were a TIFF image, since all images rendered from capture data have contrast curves applied to fit the image within the range of tonal values the format is capable of storing and to be "pleasing" to the eye. Linear-data is not pleasing to the eye because it contains too large a range of tonal levels and corresponding brightness range. It won't "look" like the original scene as the eye saw it.

When you are talking about dynamic range, you first need to ask, which range? Is it the range of brightness levels in the scene, capable of being captured by the sensor as input, capable of being rendered to output? Is it the range of brightness or tonal values you are considering?

The scene has a range of brightness values.

The recording medium (film or sensor) has a range of brightness values it is senstive (ISO comes in here) to and a range of tonal values it uses to express those values. The brightness levels are translated to those tonal levels (whether represented by density in analog film or by numbers in digital data).

The output medium has a range of tonal levels it is capable of storing and expressing as brightness values when viewed.

The complications come because of the need to match the range and step of tonal levels in the input to the output. Further complicating things is that the JPEG image has its own set of curves and translations, when printed the printer paper and inks place their own set of limitations and curves on the translation. The environment in which the image is viewed has its own limitations and effects on the brightness values percieved.

The capability of a camera or sensor cannot be judged by looking at a random example of output from a camera's JPEG engine. That would be the equivalent of judging a film by the quality of processing and printing from a randomly selected corner drugstore.




11 February 2009

The Social Book

Should books be a calm refuge from the hubbub of the network or should they be part of the flow with constantly updated social activity right in the book? As ebooks become social that is an important question. Do people want to curl up with a good book to get away from it all, or will they want to constantly stay in touch with the author and other readers? I do not have the answer to that question, but it is clear the next step in electronic books is to make them truly dynamic, with more than just the ability to search full text or submit HTML forms. The next step in ebooks will be the integration of the social network, bringing community inside the ebook. As we begin to read books on devices ranging from the iPhone to Kindle, the possibility for connecting the text to its context of authors and fans, of creating a social context for the work in the same way Twitter creates a social context, grows.

A thought occurred to me reading about Why is OpenOffice "profoundly sick"? http://news.cnet.com/8301-13505_3-10129764-16.html that development on an office suite is no longer challenging (and has not been for a decade) to most coders. I believe this is why there is so little interest in coders working on it. But making OO into a platform for ebook publishing and integrating the social network into document creation, sharing and reading,

This is already happening piecemeal. I've gleaned information from histories of chats I've participated in, collected postings from forums, email, to use in a document and I see others doing it as well. We already are writing in a social environment. Wikis are another existing socially networked writing environment and have been since day one.

If you look at the emergence of source control services like Assembla or Google code, online "forges" for producing software, I don't see why that can't happen with ebooks. It might be a better approach than creating a desktop application.

Think of how one could incorporate content from Twitter flows, Flickr photostreams, every fourm thread, QnA question answered well, everything gleaned from the flow of socially networked information directly into ebooks through some curation and publishing process. Anything can become an ebook, and ebooks can be small or large, read on the iphone or Kindle.