News and Views from Dave Wilson

Archive for March, 2011

PhotoNetCast #56 – The Art and Business of HDR Photography

by on Mar.27, 2011, under Photography

Episode 56 of PhotoNetCast has just been published and you can find it on the site or over on iTunes. The uncut video of the original recording is also available to give you a better appreciation of what a good job Antonio does in editing the audio version 🙂


PhotoNetCast #56 – Art and Business of HDR Photography, with Trey Ratcliff from PhotoNetCast on Vimeo.

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Guest Post on “Light as Magic”

by on Mar.23, 2011, under Photography

Justin Balog recently asked me if I would contribute a guest post to his “Light as Magic” blog to be part of the “Outside Their Front Door” series. The idea here is that photographers provide a set of images taken within easy striking distance of their home so I did my bit for Austin tourism and joined in. You can see the results here.

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Photographers for Japan

by on Mar.16, 2011, under News Commentary, Photography

After last week’s terrible earthquake and tsunami in Japan, a group of photographers and bloggers led by Oliver Fluck have decided to help out by donating print sale profits to aid in the recovery effort. I am joining this project so will be donating 100% of profits made from any print or merchandise sale via ImageKind, SmugMug or my photoblog between now and April 15th to the American Red Cross.

These sites offer various print sizes with costs from $3 for a greeting card up to $1000+ for a large canvas but there should be something there for every pocket. SmugMug also sells other items like fridge magnets, T-shirts, mouse pads and other similar gift items.

These other photographers are taking part in this effort:

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FRC New York Regional 2011

by on Mar.16, 2011, under Miscellaneous

I’ve just uploaded my photos from the FIRST Robotics Competition New York City Regional. You can find them on SmugMug here. The images are set up for at-cost printing and 1 cent downloads (since SmugMug requires me to set some price before enabling the service). These are free for personal use and for activities promoting FIRST (school newspapers, posters, team publicity, TV, etc). No commercial use is permitted.

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First Robotics and Inspiration

by on Mar.15, 2011, under Photography


I think it’s pretty fair to assume that most readers of this blog can list a line of relatives, teachers, mentors, pastors, coaches and others who guided and inspired us, ultimately leading us into our careers as engineers, scientists, technologists, administrators, salespeople, marketers, designers, artists and any number of other jobs.

As a child growing up in the 70s and going through college in the 80s, I remember being in awe of the engineers and astronauts at NASA during the final years of the Apollo program and throughout the development and launch of the Space Shuttle. As a Brit, though, with little prospect of working for the US space agency, local technologists soon joined the list – Sir Clive Sinclair and the engineers at Sinclair Research who developed home computers that I could actually afford and later the team at Acorn Micro who laid the foundations of the company that is a household name today and whose microprocessors are at the heart of every TI Stellaris MCU – ARM. Closer to home, my High School science and mathematics teachers showed me the beauty and, despite society’s attempts to suggest otherwise, fun of physics, chemistry, geometry, trigonometry and calculus.

So why a post about inspiration today? I’ve just returned from a trip to the FIRST Robotics Competition New York City Regional where I was supporting TI’s Jaguar motor speed controllers. This event pitted teams from as far afield as Hawaii, Brazil and the UK against one another in a competition to design and build a robot intended to collect and place various inflatable game pieces. You can read more about this year’s game here but the most important thing to realize about FRC and the FIRST organization in general is that robots are merely a catalyst. The real name of the game is inspiration – getting the next generation passionate about science and technology and steering them towards the careers which will develop tomorrow’s technologies and drive tomorrow’s economy.

Each team requires many skills to complete the game challenge. In addition to the obvious hardware and software tasks, experts in sales, marketing and design are needed for publicity and fundraising, and administration skills are in great demand when trying to arrange transport and accommodation for teams of up to 40 people who may have to travel across the state, across the country or even across the ocean to attend their chosen FRC event. For each of these activities, the team relies on an army of mentors to advise and assist. Teachers, parents and professionals give up a significant portion of their free time to help team members come to grips with the new skills required and, at the same time, teach them a real-world lesson in how to break down and handle a complex task in a team setting. This is the kind of experience that schools are, frankly, just not set up to provide and it’s also exactly the kind of experience that gives kids who take part in FIRST programs an advantage in the job market.

As professionals ourselves, FIRST and programs like it offer us outstanding opportunities to give back to the community, inspiring tomorrow’s professionals and helping prepare them to follow in our footsteps. Remember, too, that inspiration goes both ways – the energy, enthusiasm and creativity of the kids on the team definitely revitalizes the mentors too. If you have some time on your hands and a desire to get involved in something that really makes a difference in the lives of young people, take a look at FIRST and see how you can fit in to help a truly inspirational organization.

This post originally appeared in Texas Instruments’ “TI Live @” blog and has since been republished in Electronic Component News.

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HDR Tip #7 – Magic Blue Sky Halo Removal

by on Mar.06, 2011, under Photography

Here’s the last of my HDR tips for this week. I’ve been saving this one for a while but, if you shoot in climates where you can rely upon clear blue skies, it’s a killer tip and could save you hours (even if I do say so myself).

Do you often find yourself with a mess like the following after tone-mapping? Frankly, this is an image I really don’t like – the tone mapping is wildy unsubtle but it serves as a great example for this tip.
Fort Bend County Courthouse (before)

The foreground looks the way it was intended to look but the sky is a horrible collection of haloes and weird areas of different shades of blue. Wouldn’t it be great if I could just drop in a new sky without having to spend a week masking around all those blasted leaves? Well here’s a tip that will fix your sky in about 2 minutes flat as long as it’s predominantly blue. This will work if there are some clouds but it definitely works best when the sky is clear.

Take a look at the original brackets you used and decide which one has the best sky tone. I typically like the -2EV image since I like nice, dark, saturated skies but it’s entirely up to you. Open the tone mapped image and the original image with the good sky as layers in Photoshop with the tone-mapped image below the original bracket.

Now we’re going to use a bit of magic that very few people seem to know about. Make sure your magnification is set so that you can see the whole sky area of the image then right click on the top layer (with the original image) and select “Blending options…” (in CS5 at any rate. It used to be called “Advanced Blending…” or something similar in some previous versions as far as I can remember and you accessed it from the layer effects list I think). The dialog that you will see allows you to control how this layer blends with the one below it and one of the great features it offers is the ability to blend based on the colours in either this layer or the one below it.

As you will notice, the bits of the tone-mapped image we want to replace correspond with the blue sky in the original image so let’s tell Photoshop to show the original only where it is predominantly blue. Do this by setting the “Blend If” option to “Blue” then drag the slider under “This Layer” to the right. As you do this, you will see that the underlying layer starts to bleed through and become visible. Move the slider to the right until you start to see chunks of the tone-mapped sky appearing then stop. At this point, you will notice something along the lines of the following:
Advanced Blending

The original sky is definitely visible but you will also see a lot of really horrid fringes around all the tone-mapped leaves. There’s another secret to get rid of these. Hold the “Alt” key and click on the slider you just dragged. You will notice that it splits in two so now grab the left hand half-slider and pull it back towards the left. As you do this, you should see the fringes get smaller and, eventually disappear leaving you with something like this:
Advanced Blending (after splitting the slider)

You will likely have to juggle the left and right half slider positions to get the best overall effect. It’s a good idea to zoom to 100% to check out the fringes since it’s tricky to see how the individual leaves (or other edges) look when you are zoomed out.

Once you have marveled at how the sky looks, you may be disappointed to notice that this blending has had a muting effect on other sections of the image too. This can, however, be corrected very easily by adding a layer mask to the top (original image) layer and, using a soft-edged brush, painting in black over the areas that you don’t want to be affected. Doing this, you are effectively allowing the underlying tone-mapped layer to shine through completely unaffected. If you accidentally paint any of the sky, just switch to white and paint the mask with that to erase the effect. Typically, the effect on non-sky sections of the image is reasonably subtle so you don’t have to be enormously careful when you are doing this final masking step. Painting this mask is, of course, enormously easier than trying to figure out how to mask around all the leaves!

Here’s the final version of the image I started with after about 2 minutes of slider juggling and some easy mask painting.
Fort Bend County Courthouse (after sky replacement)

Hopefully you’ll find this tip useful. It’s saved me hours here in Texas where blue skies are the norm. If you live up north or across the pond, you may find this less helpful but the basic approach can still be used for many other cases where you want to blend based on the colour of particular regions of an image.

I hope you’ve found this week of HDR tips helpful. Thanks for reading!

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HDR Tip #6 – How Many Exposures Should You Shoot?

by on Mar.05, 2011, under Photography

Yes – I’m copping out on this one since it was published a month or so ago on Scott Wyden’s blog as a guest post. However, here it is again, with a few updates and corrections, since I still think it’s a good tip…


St. Mary's Roman Catholic Church, Lanark
I’m often asked how many exposures I use for my HDR images and tend to make myself unpopular by answering “As many as it takes.” This sounds glib but it is, in fact, the truth. Some people appear to be under the impression that you can get by with always shooting, for example, 3 images spaced 2 stops apart. This may work most of the time but that will likely be by luck rather than design. An outdoor scene will probably be captured fine using exposures from -2EV to +2EV but inside a cathedral with bright, stained glass windows, for example, it can take 11 shots (or more) spaced 1 stop apart (-5EV to +5EV) to capture the full dynamic range.

The point of bracketing for HDR is to ensure that you capture the entire dynamic range of the scene – as much shadow detail as you can get and all the highlights. To do this, you really have to check your histogram after taking a basic set of bracketed exposures and add to this set if needed.

These days, I typically start with either 5 or 7 images bracketed by 1 stop. The initial choice will depend upon the scene I’m shooting and my assessment of the dynamic range but it doesn’t really matter as long as you follow the next step. Once the initial bracket is done, make sure you don’t move the camera but review the brackets on your LCD with the histograms visible. The darkest image should have no blown out highlights (if you have the ability to turn on “blinkies” to warn of this, that’s really helpful) and you should see no significant bunching of data on the right of the histogram. The lightest image should have no solid shadows (data touching the left edge of the histogram). To be extra safe and to reduce noise in the shadow areas, I always try to ensure that my lightest exposure has no data at all in the bottom quarter of the histogram.

One other thing to beware of when looking at your histogram is whether any particular colour channel is blown out. The standard, single luminance histogram doesn’t give you the whole story here but most cameras allow you to look at a display containing independent histograms for red, green and blue channels so it’s a good idea to use these instead and make sure you apply the rules across all three. No channel should have right edge clipping in the darkest shot and no channel should have significant data in the left quarter of its histogram in the brightest shot. Thanks to Dave Nightingale for this particular suggestion!

If you find that your outer exposures don’t meet the criteria given above, carefully turn off auto-bracketing (if you were using it) and dial in exposure compensation to allow you to shoot exposures on either end of your original bracket. If I shot a 5 image bracket (-2EV, -1EV, 0EV, +1EV, +2EV) , for example, and see that my darkest image still has blown out highlights, I will dial in -3EV and take another shot before checking and repeating as necessary. Most of the time, I shoot in manual mode with my camera set to change shutter speed in half stop steps since it makes this process a bit easier. I can turn off auto-bracketing then click my thumbwheel the correct number of times to change the exposure as required for the other shots I need to take.

This brings up another comment I hear frequently from many photographers who state that their camera can only shoot 3 frames in auto-bracketing and, hence, they can’t bracket any wider than that. Remember that auto-bracketing is merely a tool that makes things a bit easier. Even if your camera can only take 3 shots in a sequence, you can still turn the automatic mode off and dial in the required exposures by hand as I do to widen your bracketed exposure range. Another option, if you have money to spare and a compatible DSLR, may be to purchase a Promote Control
which will allow you to dial in the larger number of exposures without touching the camera at all but, even without this, a bit of control tweaking is all it takes to capture the full dynamic range of any scene you are shooting.

By making sure you capture the full dynamic range of the scene, you are certain to notice better final results – lower noise in the shadows, fewer blown-out highlights and generally cleaner images. Next time you are asked how many exposures it takes to produce an HDR, remember to answer “As many as it takes” and be ready for a longer discussion!

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HDR Tip #5 – Great Sky and Great Foreground

by on Mar.05, 2011, under Photography


Texas State Capitol

Quite often, I find that the tone mapping settings I like for part of my image cause other parts to look bad. In these cases, if I’m going for an artistic look, I will save the .HDR or .EXR file from Photomatix then open it twice and tone map it with settings that look good for each area independently. I then take these images into Photoshop and blend them together to give me the look I want in both areas.

If you are generating a realistic looking image, you can usually get away with not re-tonemapping but just blending in one of the original exposures. This is something I frequently do to get rid of blown highlights, noisy sections or weird contrast inversions in skies while keeping the tone mapped look of the foreground.

Open both of your tone-mapped images (or the original and tonemapped image) as layers in Photoshop with the main image on the bottom. Add a layer mask to the top image then fill the mask with black. Using a soft-edged, white brush, paint into the layer mask in the areas that you want the top image to be visible (the sky, for example). Once you’ve done this, you can change the opacity of the top layer to vary the amount of the original effect you let through.

Before anyone complains, I should admit that the picture at the top of this post is not the final version of this particular image since I’ve not uploaded that one to Flickr (you can see it on ImageKind and SmugMug though if you are interested). The final version fixes all the highlights in the clouds using this method.

I have another tip for fixing sky problems coming up but I think I’ll hang on to that one for a couple more days!

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HDR Tip #4 – Dealing with Colour Fringes

by on Mar.03, 2011, under Photography


Senate Chamber, Texas State Capitol

Another of my golden rules for processing HDRs is to do as little as possible to the brackets in Lightroom before I export them to Photomatix for merging. The main reason for this is that I want to ensure that I don’t disturb the pixels in each of the bracketed exposures differently and run the risk of messing up Photomatix ability to merge the picture but it’s also because I think of Photomatix as the first step in the process. There are, however, two operations that I typically do before merging the brackets, one of which is cosmetic and the other of which is, in my opinion, absolutely vital.

The cosmetic operation is to correct the image white balance if I didn’t nail it in the camera. The important thing here is to make sure you apply exactly the same change to every one of the pictures in the bracket. Typically, I will correct the center exposure then use the Develop Setting copy/paste operation in Lightroom to apply the same setting to the other images. I do most of my colour correction or tweaking after Photomatix is done with the image but it’s always easier to start with images that are close to where you want to end up.

The more critical operation for me, however, is correcting chromatic aberration. This is a “feature” of lenses (typically cheaper ones, to be honest) caused by the fact that they focus different colour of light at slightly different distances and, hence, give slightly different magnifications to the red and blue channels in the image. This results in colour fringing along high contrast edges near the sides of the image. If you don’t correct this prior to merging, you will find that (a) you end up with an HDR that is less sharp than it could be and (b) the fringing effect will be magnified an enormous amount by Photomatix.

If you are lucky enough to be using very high quality professional lenses, you may never see this (I really only have to deal with it on my Sigma 15mm fisheye since the Nikon pro lenses I have are amazingly clear of CA problems) but most of the time it will be apparent if you zoom your image to 100% and take a look at the corners. If you are using Lightroom, correcting the problem is very simple. In the Develop module, look under “Lens Corrections”. If Lightroom knows about your particular lens (and it knows about a lot of lenses), you can click “Profile” then select “Enable Profile Corrections” and your CA problems will disappear immediately. Note that this also allows you to correct lens distortion and vignetting but I typically leave these set to 0 since I like the fisheye distortion and the vignette doesn’t worry me.

If Lightroom doesn’t know about your particular lens, click on “Manual” and fiddle with the sliders under “Chromatic Aberration” until the fringes you see in the image disappear (or get as small as you can make them). In both the manual and profile cases, make sure you apply exactly the same setting to all the images in your bracket then go ahead and export them to Photomatix.

I’ve added an example of before and after here so that you can see what I am talking about. The top image shows a 200% view of the top right corner of one of my brackets before CA correction and the bottom one shows the same section after automatic CA correction in Lightroom.


Before Chromatic Aberration Correction

After Chromatic Aberration Correction

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HDR Tip #3 – Thwarting the Tripod Police

by on Mar.02, 2011, under Photography


St Patrick's Cathedral, New York City

As any dedicated HDR photographer will tell you, you should be carrying a tripod with you at all times. Even if you are carrying your tripod, however, it’s not guaranteed that you will actually be able to use it. Many buildings prohibit tripod use and many security guards get all hot and bothered when anyone walks into their territory carrying one. Despite this (and I won’t get started on how annoying and pointless some of these situations can be in this post) you can often save the day if you are also carrying a small and pretty inexpensive piece of equipment.

I have two Joby Gorillapods – an SLR-Zoom model and the larger, sturdier Gorillapod Focus. Frequently the same people who complain loudly if you even think of setting up a tripod won’t bat an eye if you pull out a Gorillapod and use that instead.

The picture shown here was taken with my D90 on the Gorillapod SLR-Zoom in St. Patrick’s Cathedral, New York, a place where tripods are completely verboten. I had to remove the camera’s battery pack and restrict myself to a smallish lens (this was shot with the Sigma 10-20mm) since the SLR-Zoom model, from my experience at least, really isn’t sturdy enough for anything but the lightest body/lens combination. Regardless of only having this small tripod-replacement, I managed to get some great shots by clamping the bendy legs of the Gorillapod onto the top of one of the cathedral pews. In some places, the fact that you can attach the Gorillapod to posts, furniture, fences, etc. actually gives you better camera-positioning options than you would have with a traditional tripod.

The newer Gorillapod Focus model is intended for larger cameras and can handle the weight of a pro-body with battery pack and a decent sized lens. For even more flexibility, add a small ball head to allow easier adjustment of the camera position. I have Joby’s own ballhead for the Focus and a small, generic ballhead on the SLR-Zoom.

Next time you find yourself having to use your tripod as a walking stick because some officious security guard tells you you can’t use it, save the day by trying to use a “non-tripod” instead and see if you can get away with that. I expect you will be pleasantly surprised.

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