News and Views from Dave Wilson

Computer

FIRST Kick-off Almost Here

by on Jan.06, 2010, under Computer, Miscellaneous

If you have read this blog for any length of time, you will know that I highly approve of Dean Kamen’s FIRST organisation. This weekend sees the kick-off for the 2010 FRC competition and the start of the 6 week design and build period leading up to regional competitions in March and April. If you can make it to any of the events, I would encourage you to go along and see just how cool they are. Talking of cool, they even managed to get Neo to do a PSA spot for them this year…



Edit: A more knowledgeable colleague just pointed out that the Keanu PSA was actually prepared for last year’s competition. That answers my question about why it doesn’t contain any footage from the 2009 competition. Oh well…

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Musings on Dynamic Range, Bits and Stops

by on Dec.28, 2009, under Computer, Photography

I got into a conversation with Guy Tal, Jim Goldstein and Pete Carr on Twitter this afternoon and it quickly became clear that it wasn’t going to work in 140 character chunks so I reckoned a blog post would be in order. This is something I’ve been meaning to write about for a while now so I’m happy I now have an excuse.

The issue under discussion related to the relationship between the number of bits used to store a High Dynamic Range image and the light levels that the image can store. An HDR image is typically thought of as being represented with 32 bits per color component (32 bits of red, 32 bits of green and 32 bits of blue for every pixel). Some of the most common HDR file formats actually use less than 32 bits per pixel but, regardless, the question comes up about what each of those bits represents and how the number of bits dictates whether an image is “High Dynamic Range” or not.

I had always assumed that the dynamic range of an image depended to some extent on the absolute maximum light level that could be recorded. On reading Christian Bloch’s rather good “HDRI Handbook” last year, I was surprised, however, to read that the dynamic range is defined instead in terms of the ratio of the number of discrete values (2**32, for example if we’re talking about a 32 bit number) a measurement can represent divided by the smallest measurable difference (the change in the signal represented by 1 least significant bit). Nowhere in this calculation does any absolute value appear – the dynamic range is a ratio of the largest and smallest values that can be represented but it says nothing about the actual quantities that those values represent.

This didn’t seem intuitive to me. Where was the reference? How would you know how bright a given pixel would be? Thinking about this for a while, however, it became clear that I was forgetting to take into account the camera as a whole rather than merely the sensor.

The camera’s sensor has a fixed, maximum signal that it can record and a certain number of bits of resolution. For example, a 12-bit sensor can differentiate between 2**12 (or 4096) different levels of red, green and blue light. At some absolute level of light, the sensor saturates and outputs its maximum value. If you increase the light level falling on the sensor above this amount either by keeping the sensor exposed to the light for longer or by increasing the brightness of the light falling on the sensor, you get no new information and the signal stays saturated.

Thinking about this from a photography point of view, however, this is exactly as you would expect and corresponds to overexposure. In this case, we close the aperture, reducing the brightness falling on the sensor, or speed up the shutter to reduce the total amount of time the sensor is exposed to the light. These changes reduce the total amount of light falling on the sensor and allow us to take another, hopefully correctly exposed image. Although the maximum light level the sensor sees has dropped and it no longer saturates, it still records 4096 different levels falling on it. The recorded dynamic range is the same but we’ve shifted the recorded values so that all of the actual image brightness levels fall within the recording capabilities of the sensor.

This is exactly as you would expect in a film camera too – if the film is overexposed, it “saturates” to opaque and you can’t store any more information (there is the complication of logarithmic vs. linear response here but let’s gloss over that for now since it’s not really relevant to this discussion). In these cases, you reduce your exposure to get the amount of light hitting the film such that you don’t saturate the medium.

Considering things this way, it is now clear (to me at least) that the absolute value of light represented by the sensor’s (or film’s) maximum output value is irrelevant. The photographer adjusts the exposure to ensure that the brightest highlight in the image is at or just below the sensor’s saturation point and, hey presto, you end up taking maximum advantage of the sensor’s dynamic range. The absolute maximum light level that will cause the sensor to saturate is, therefore, related to the sensitivity and not the dynamic range. If the sensor saturates with very little light hitting it, we end up with a high sensitivity (or high ISO) sensor that allows us to record images in lower light than one which saturates at higher light levels.

So how does this tie back in to the normal photographic system of defining exposure in terms of stops or EVs? For every bit you add to a sensor, the number of values it can represent doubles and, as a result, its theoretical dynamic range will also double (forgetting about noise which reduces this somewhat). Thinking about exposure calculations, you know that increasing your exposure by a stop also doubles the amount of light hitting the sensor. There is, therefore, a direct correlation between 1 stop and 1 bit. Reducing your exposure by a stop divides the sensor output in two or shifts the value one bit to the right. Adding a stop to your exposure does the opposite, doubling the sensor output or shifting the value one place to the left.

Using the bit shifting idea, we can, therefore, get some idea of how much dynamic range an HDR image may have based upon how we recorded it. I typically use 3 images bracketed 2 stops apart when shooting HDRs. If the original scene contains very bright highlights or lots of dark shadow areas, I will use more brackets but 3 is usually enough. My Nikon D90 has a 12 bit sensor and, at low ISO values, has close to .12 bits or 4096 levels of dynamic range. Adding +2 stops to the exposure has the effect of multiplying the sensor output values by 2**2 or 4 or shifting them 2 bits to the left. Taking away 2 stops has the opposite effect, dividing the output values by 4 or shifting them 2 bits to the right. When I combine all three exposures, -2 stops, 0 stops, +2 stops, into an HDR image, therefore, the maximum dynamic range I could possibly record would be 12 + 2 + 2 bits or 16 bits of information. Even though I may save this image in a 32 bit file format, I’m not actually storing pixel values that extend from the lowest to the highest possible value in the file format. Regardless of the fact that I’m not using the full dynamic range of the recording system (the 32 bit pixel component representation), I still have 16 bits of information per colour component which is twice the number of bits I would have had if I had saved in JPEG and 4 bits (or 16 times) more than I would have got from a single RAW file from the camera. The dynamic range of my image is something like 65536:1 versus 256:1 for JPEG or 4096:1 for my 12 bit RAW format.

Confused? If so, leave a comment and I’ll try to clarify this a bit!

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The Sky’s (not) The Limit

by on Sep.08, 2009, under Computer

I’m trying something new this morning. This post is being typed and posted from somewhere around 30,000 feet above south eastern Oklahoma thanks to the wonders of American Airlines new inflight WiFi. For $10, I get a broadband connection from my airliner seat – how amazing is that? I had expected a dial-up type experience but the bandwidth is actually rather impressive – streaming video, at least of the standard definition variety, plays smoothly and I’ve noticed no delays significantly longer than I would nornally see at home or in the office. Obviously, I have no idea how many people are using the service but I have to imagine that a full flight such as this containing mostly business people would be using the service pretty heavily.

The downside of this, of course, is that flights are no longer an opportunity to read, play games or generally do non-work things (like post to blogs?) during work time. I guess I had better get back to the email….

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Animusic

by on Aug.09, 2009, under Computer, Miscellaneous

When I was working in digital settop box software, one of the biggest problems we used to have was ensuring that the audio and video stayed synchronised with one another. Arguably there’s nothing worse in TV playback than having the audio run slightly ahead of the video – even a 10mS audio lead is really noticeable and really messes up your viewing experience. Interestingly enough, if the audio is significantly behind the video (up to 100mS or so), you don’t worry so much since your brain is used to compensating for the delay caused by the speed of sound being so slow. I digress, however…

This morning, my 6 year old son introduced me to some videos on YouTube that give a whole new meaning to audio/video synchronisation. These animations do a superb job of synchronising the animated video content with the soundtrack. They are completely mesmerising. Take a look at this one then head over to YouTube for various others. You can buy DVDs at www.animusic.com.



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The Joys of Automatic Translation

by on Apr.25, 2009, under Computer, Miscellaneous

I just received a rather odd message via Flickr mail. It was from an Italian photographer advertising one of his images. It was also in Italian, a language which is not my best (I barely know how to order beer in Italy let alone carry on a conversation about photography). As I usually do, I headed over to Yahoo Babelfish (or http://babelfish.altavista.com as it used to be – oddly, the “legacy URL” still works nicely) and pasted in the text. The final paragraph of the original message was:

“Flickr è la migliore applicazione per la gestione e la condivisione di foto online. Se sei curioso di sapere per che cosa lo utilizzo, guarda il mio profilo oppure naviga tra il mio album.”

…and the web site translated this as:

“Flickr is the best application for the management and the sharing of photo online. If you are curious of knowing for I use it what, watches my profile or is annoying between my egg whites.”

I do find unsolicited messages like this rather annoying (though I think this was the first example of Flickr spam I have seen) but, in this case, it ended up having great entertainment value and didn’t disturb my egg whites at all.

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Prints and eCards from the photoblog

by on Apr.21, 2009, under Computer, Photography

A couple of days ago, I heard about a new company in California offering an excellent service to photographers. Fotomoto offers the ability to provide print purchases directly from your web site without the need to tag, keyword and upload high resolution images to yet another site. I applied to join their beta program and was invited this evening.

Setting the service up on my photoblog was trivially simple. After logging on to the Fotomoto site and setting pricing for the various print sizes, I copied a small block of JavaScript and pasted it into the footer of the photoblog page. Immediately, all the images have a couple of new, unobtrusive links added beneath them, one to allow print purchases and the other offering to send an eCard containing the image.

Some of my images were taken in places which do not allow commercial sale of photographs taken there and one was taken with an old digital camera whose resolution was not really up to producing high quality prints so I had to return to the Fotomoto control panel to indicate which images were not for sale. Overall, the installation and customisation was incredibly easy.

So far, this looks as if it should be a superb service. I’ll purchase a couple of test prints and report back once I have checked out the print quality. Assuming it’s on a par with ImageKind, I will likely move all my online print purchasing there since FotoMoto do not charge an annual fee (they take a 15% commission on each sale instead which, given my current sales volume, works out better for me)

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HDR Notes for PhotoNetCast Listeners

by on Apr.10, 2009, under Computer, Photography

Farmhouse PorchI’m posting this right after recording PhotoNetCast #27 in which I was invited to join a discussion on High Dynamic Range (HDR) photography. These notes are intended to provide a bit more information and a few pointers if you are interested in looking at the kinds of images we will be discussing and also learning how to produce tone-mapped HDR images for yourself.

Some Examples of Good HDR

Photographic tastes are very personal but, to get things started, I would recommend looking through the work of some of these folks who I think do a fantastic job of showing HDR techniques used extremely well. I would be foolish to suggest that these are the best HDR photographers on Flickr but they are certainly the ones whose work I follow closely and very much enjoy. These are in no particular order.

  • Trey Ratcliff (stuckincustoms) is probably known by many as the king of HDR. He travels extensively and posts new photos daily. His blog is also well worth following and is a great place to start if you are looking for an HDR tutorial.
  • ~EvidencE~ (who doesn’t provide a real name) posts wonderful examples of HDR depicting industrial scenes and decay, in addition to some superb landscapes.
  • Roman Solowiej (shexbeer) also concentrates on images of decay and destruction where HDR techniques are used to great effect to accentuate texture.
  • Karl Williams (Shuggie!!) takes wonderful urban and landscape images using HDR techniques for the majority of his pictures. Many of Karl’s images are taken around my old stamping grounds in Glasgow, Scotland.
  • Erlend Robaye (Erroba) produces beautiful citiscapes and abstracts using HDR techniques.
  • Jerry Hayes (JerryHayesAustin) is a local photographer with whom I have had the pleasure of shooting a few times. I’m linking to his set of Special Event Photography images since these are fabulous examples of how HDR can be used subtly to produce natural looking results in tricky lighting situations.
  • Steve Sawford (Steel Steve) is another UK-based photographer whose urban HDRs taken in the industrial north of England are superb.
  • Raul Pires Coelho (raul_pc) is based in Portugal but posts urban and cityscape HDRs from around Europe.
  • Sarah Peters (sarah_peters1) is based in the town of Douglas in Scotland (9 miles from my home town, as it happens) and uses HDR techniques on many of her stunning landscape shots. Again, her images show wonderful use of HDR to produce natural-looking results.

Books

Wrecked Fire Truck

There are loads of web-based resources for learning HDR but I find having a good old fashioned book a great way to learn. Here are three that I particularly like.

  • The HDRI Handbook” – Christian Bloch. I found this book extremely helpful but it would probably be better read after having worked with HDR for a while since it covers a fair bit of theory. It does a great job of comparing software tools and also comes with a CD containing various images and evaluation copies of some of the tools.
  • The Complete Guide to High Dynamic Range Digital Photography” – Ferrell McCollough. I’ve just bought this book and have not yet had a chance to read it through. From what I have seen, however, it looks to be a very practical guide and probably a great book to read as someone wanting to start shooting HDR images.
  • Mastering HDR Photography” – Michael Freeman. I picked this book up and had a look through it in our local book store recently and was very impressed. It covers a lot of ground and has a very good mix of technical and practical information.

Software

Old Filling Station, Driftwood, Texas

I use a combination of Adobe Lightroom 2, Adobe Photoshop CS3 and HDRSoft Photomatix to produce my HDR images. You can do the vast majority of the work in Photomatix alone but I find that Photoshop does a better job of merging images if there is any movement between the exposures and I feel that I get better images if I use the Photomatix export filter for Lightroom rather than loading the raw NEF files directly into Photomatix . Regardless of which tool I use to generate the HDR file, I always use Photomatix for my tone mapping. HDRSoft offer an evaluation version of Photomatix which watermarks its output and also a useful tutorial to get you started. The tool itself costs $99 but if you use coupon code “DaveWilson” when you are checking out, you will get a 15% discount.

Another tool I have played with briefly is Ariea HDR Max. This has a more polished user interface than Photomatix and one feature that I really like – the ability to turn on and off the contribution of any single exposure to the final HDR. That said, I found the tone mapping settings less flexible than Photomatix and had trouble especially with the gamma slider which seemed to generate enormous changes in the image with tiny movements. This may be fixed now and I would encourage you to download this trial version too to see how you like it.

I also have FDRTools on my “must check this out” list. I’ve seen some superb images created using this software but have yet to download the trial and play with it. The package is very inexpensive and endorsed by some of the big names in the HDR world so it’s definitely worth a look too.

Many, many other freeware and commercial tools exist to generate HDRs and tone map them so try as many as you can and settle on whichever gives you results you are happiest with.

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FIRST Robotics Competition

by on Mar.01, 2009, under Computer, Miscellaneous

You have probably noticed that it’s been a bit quiet around here this week. Since Wednesday, I’ve been up in Cleveland, Ohio attending the FIRST Robotics Competition Buckeye Regional. Luminary Micro, my employer, supplied the motor speed controller units that the teams received in this year’s kit of parts so we had representatives at all the competitions this week to make sure that things ran smoothly. I’m very glad to say that they ran very well in Cleveland with only a single failure that needed replacement during the 3 days of matches.

The FIRST (For Inspiration and Recognition of Science and Technology) organisation was founded by Dean Kamen (of Segway fame) to “transform our culture by creating a world where science and technology are celebrated and where young people dream of becoming science and technology heroes.” and, as far as I can see, it is doing an outstanding job. The competitive side of the program is completely secondary – yes, you get to compete against 60 or so other teams at a regional like this but the really important part of being there is to meet the other teams, exchange ideas and help out the rookies (and anyone else needing material or expertise that you can provide). They call it “coopetition” and it breed a wonderful atmosphere at the events. The program strives to promote “gracious professionalism” where competitors respect each other and chest slapping and victory dances are definitely not allowed.

I had a whale of a time at the competition and will definitely be looking for more ways to stay involved with FIRST. If you have an interesting in promoting science and technology in education, you could do a great deal worse than check these folks out.

Here are a few snaps to give you a feel for the event. I should point out that the game the robots were designed for involves getting balls into trailers towed behind your opponents.


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Photomatix 3.1.3 Available

by on Feb.22, 2009, under Computer, Photography

I’ve just discovered that a new Photomatix update is available. Get hold of version 3.1.3 (with tighter Lightroom integration and the ability to automatically reimport processed images into the Lightroom catalog- yay!) here.

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