Today I’m going to talk about the nuances of High Dynamic Range photography, sometimes referred to as HDRI , the ‘I’ denotes ‘Imaging’. Now I do not pretend to be an expert in this kind of photography, but I know enough to be able to explain it to you in the simplest terms possible. The image above is HDR, but not in the true sense of the word as I made it from a blank canvas in Photoshop (isn’t it cool!?), created three duplicates and then exported them into Photomatix with 2 exposure stops between each image (+2, 0, -2), then merged them to HDR. I’ll explain this later, as in my opinion this is cheating. It’s quick but it leaves me feeling dirty afterwards!
So. What does it really mean? Sometimes you might want to take one photo to capture all the range of shadows, contrast and highlights, but unless you have filters this is pretty difficult to do. Enter HDR. Our eyes can capture approximately 10 – 14 f/stops of dynamic range, whereas something like a compact camera can only pickup between 5 – 7 f/stops and a DSLR will have a range of around 8 – 11 f/stops. So, from this we can deduce that a camera taking a single shot cannot always capture the dynamic range in any given scene and as light varies so massively from day to day, it’s quite a task. You know what I’m talking about; you’re taking a shot using your LCD screen and the sky is very bright and the ground is too dark, so you have to keep twisting the camera up and down to try and balance both? That’s the problem. So we have to use a technique called exposure bracketing, if your camera is capable of it. Which I’ll discuss now, if you’re still interested enough to read my drivel.
This is where a tripod comes in very useful. Basically, more advanced cameras (and it doesn’t have to be a DSLR, mine isn’t) have this facility and usually will allow anywhere between 3 and 5 stops of exposure. First, set up your camera on the tripod and compose your shot exactly where you want it and lock it in place. On my camera I have to set it to Av mode (Aperture Priority), then look in your camera settings (you have read your camera manual, I assume?) for something called AEB (Auto Exposure Bracketing), look at the settings and decide how many stops of exposure you want to set between each shot; I generally use 2 stops but it can depend on the light and whether you’re shooting towards the sun or not, which will require more exposures. If this is the case, you can do this manually; don’t be afraid of setting your camera to manual, you’ll get the best from it!
The problem here is that between each exposure, the camera settings need to be adjusted for the next exposure, so there is a risk of the camera moving; even the smallest movement can effect how your images turn out. If you own a remote, then set your shutter release off this way, if not, to prevent movement set each exposure with the camera timer, but if you do it this way, set the timer long enough for the camera’s micro-vibrations to stop after you’ve touched it especially if you are zoomed in as this unbalances the camera slightly; I work between 5 and 10 seconds. If it’s windy, try and weigh down your tripod.
Now, set off your shutter release (the button that takes the picture; I said I wanted to keep it simple 😉 and allow the camera to do its work. It will take three shots (if this is the only option you have) at the different exposures you set, whether that was 1/3, 1/2, 1 or 2 stops; this will also depend on your camera so read the manual! If you’re taking more than one image and so you can easily differentiate between your images, a good thing to do when it’s finished shooting, is take one shot of your hand; this shows you when one set ends and another starts – it’ll really help you in post-processing! I do this when shooting panoramas with a number of shots.
Another important point to note is that if your camera has the ability to shoot in RAW instead of JPEG, then do so; set the camera to take ‘RAW+JPEG’ in the settings. Shooting in RAW mode gives you much more flexibility when it comes to adjusting your images and what you see is what you get with RAW; it records what it sees and is completely lossless, meaning that there is no data removed from the image in camera or compressed in any way. JPEGs are lossy as they are adjusted in camera with sharpening, contrast and shadow adjustments plus it is compressed. To give you an idea, if I shoot in JPEG at the maximum resolution (12.1MP) at 100 ISO (more on this another day) the file size will be between 2 and 3MB; the RAW file comes out at 18MB; a big difference so ensure you’ve got a larger memory card, at least 8GB. You will however need dedicated software that can recognise RAW formats; here’s a few variables: Canon – .CR2, Nikon – .NEF, Olympus – .ORF, Pentax – .pef. There are many more as they differ between manufacturers. You can use Picasa which is free or you may own Photoshop which recognises RAW formats.
Anyway, file formats aside, it’s time to get to the juicy processing part. After you’ve taken them from your camera and onto your software/hard drive, it’s time to drag them into the HDR software. There a few free ones available which are pretty good, such as Luminance HDR, Picturenaut and FDR Tools Basic, personally I use Photomatix, it’s not free but one of the most popular with a lot of editing functions.
Open your HDR software and the images you want to merge to HDR; I just drag mine to the Photomatix icon and it’ll automagically open the software. Now, I’m not going to run through how to process your image to how you want it to be, as everybody likes a different look but the important thing is; DON’T OVERDO IT! There’s lots of sliders to play around with and presets too and by all means mess about with them to see what they do to your image, but I’m going to show you a picture I took which is horrendous! But first here’s the interface for Photomatix, and some of the sliders are out of view!
And here’s a truly awful image I merged to HDR before I really knew what I was doing:
So, I’m now going to post five of my images of a sea-scape that are all pseudo-HDR and what I mean by that is, I cheated. I took these images before HDR took a hold of me. I originally took ten images in portrait mode and stitched them together in Photoshop, then I duplicated ten of them (due to the strong sunlight) and used Photomatix to apply the tonemapping effects, at five different levels of ‘HDR’. If I had to bracket these ten exposures, I would have to autobracket each portrait exposure three times, creating thirty images to work with! I will post an actual HDR image I created at the end of the post. They don’t always have to landscapes, that’s just my forte.
This is the first image which looks near enough normal, with just a few tweaks here and there. Remember, using one duplicated image will not give you the same dynamic range as actually shooting them will, otherwise we’d all be cheating:
This image I used a heavier tonemap, so although this is not over the top, it is clearly more saturated and more dynamic range than the above image:
This image is meant to appear surrealistic, as I wanted to demonstrate to you how this kind of tonemapping does not necessarily work with landscapes. However, I still do not think it is a bad image and I actually quite like it:
Here we can clearly see how going over the top with the sliders and effects can really amplify the image;
And this one, well seriously, don’t show it to your friends if you ever want to see them again:
So there we have it, five tonemapped images in varying stages. Another point to note when shooting for HDR, is the amount of noise that is generated from merging images. This will appear as speckles on your picture, usually in the midtone or darker areas; the bottom image is rife with it, compared to the first image. The more detail you apply to a photo, the more noise will increase and it can be very difficult to balance, so try and shoot at as low an ISO as possible; 100 or even 50 if your camera allows it. This will of course depend on your camera and available light but anything above ISO 1600 will generate a lot of noise; it’s created by heat from your camera’s sensor.
And so, to wrap up I will post an actual HDR image, plus one I have blended together to show a comparison. OK the fruit looks unappetising, but look at the range of shadows, contrast and highlights. You can even see into the shadows and this was taken without a flash:
This is the comparison shot, showing how even a low tonemapped (HDR’ed) image can still look very normal and how a high tonemap can put people off your fruit!
I hope you have enjoyed this post and have taken something from it. I enjoyed writing it.
I’ll ponder what to write about next!