Shoot a HDR panorama

Hardware

Before we start to shoot right away I will take a look at the required hardware and settings to get the best results. The tripod with panohead is discussed in the previous section, but I would advise you to fit a leveler between your tripod and panohead. This tool lets you level your head easily with three screws. It sure beats stunting around with extending and pushing in your tripod legs! The most important piece of hardware offcourse is your camera. preferably you will need a DSLR with some kind of bracketing features. Without bracketing feature you can shoot a 360 pano like described here, but no HDR pano. The lens you use determines the final quality and resolution of your panorama. Mostly 10.000 pixels wide will do for the most 3D purposes. When using a 10-15 megapixel camera, a fisheye lens like 8-14mm works fine. When you need more resolution, you will need a narrower field of view, like a wide-angle lens like 14-20mm, or a camera with more MP´s. You will need a cable release too, so you won’t have to touch the rig when taking you bracketed series of photos. A bubble level to slide in the flash shoe is really convenient too. To top it all we need a color calibration card or gray card to calibrate your camera colors and white balance. For perfection have your PC monitors calibrated too.

 

.JPG or .RAW?

This question depends on several things, of wich the most important one is time. Simply because RAW takes more time to shoot because the datastream multiplies by 5-10. You can have a fast card like 45MB/s, but it wont gain you much speed simply because the camera cannot deliver them fast enough, or the in-camera buffer fills up. Only if you have a couple of thousand dollars for a top-shelf model you will not have this problem. And since we are shooting on public roads often enough, we do not want to stay there too long as bumper-bait with our beloved equipment... But if you are doing a parking lot or something like this where you do have the time, by all means, shoot RAW! For post-processing RAW is just marvellous: shooting in RAW delivers you 12 or 14 bit images insted of the 8 bits of a .JPG, so you could shoot in 2 EV intervals instead of 1EV for JPG because you have a wider dynamic range in a single image. And then there is the magnificent Camera Raw plugin for photoshop. It allows color profiling and super accurate WB adjustments, and from release CS5 on, this plugin has extended lens-correction out-of-the-box. One other huge benefit with shooting in RAW is that you can apply the exact same adjsutments to your HDR and your backplates, wich guarantees you identical colors for both of them!

 


Camera settings - Bracketing

First of all lets set the bracketing. Some smaller cameras can shoot +/- 1 EV in 1 EV steps (3 shots, 2 EV total shift), while some more advanced models can shoot up to +/- 9EV in 1 EV steps (9 shots, 8 EV total shift). Some top canon models can handle 9 shots with 3 EV stops interval, giving 27 EV total shift! When using 1 stop shift, JPG file will do. When using 2 stops interval RAW is the choice, because it holds more information to create an overlap. Just keep in mind that when you shoot in RAW with 9 shots, you will need a seriously fast storage card to work fast. Even the camera buffer will fill up very fast when shooting RAW. So if you do RAW, take your time! For this example I will use 9 JPG shots, with 1 EV shift. This total shift of 8 EV is used all the way on a sunny day. On a cloudy day, when the dynamic range of the environment is smaller, you can settle for 5 shots +/- 1EV. Just remember i'm offering guidelines here, you should always check your surrounding, even on a cloudy day you might have some very dark shadows and bright highlights pushing up the dynamic range, just as you could have an equally lit environment on a bright sunny day, with no shadows keeping the dynamic range pretty small.
 


Camera settings – Exposure

We can adjust exposure with three settings: aperture, exposure time and ISO. The ISO will be fixed at 100, or lower if possible. This is because higher ISO not only produces unwanted noise, but a high ISO value also limits the dynamic range of the sensor! The aperture is determined by the field of depth. Logically we want everything sharp in focus, things nearby as well as at the horizon. Most fisheyes have a satisfying depth of field at an F number like F/5 or higher. When we concider that shifting exposure by aperture will result in images with different fields of depth, you will realize shifting exposure by aperture is no option. Remember we need totally identical images, only the brightness values may vary. This leaves the exposure time as the only available choice to adjust the exposure.

Finding the right exposure value is fairly simple. You set the camera to aperture priority, check that your exposure correction is set to zero, and metering is done on spot, and not the entire image. When you take your camera off the rig, point the spot where the exposure value is measured at some bright areas, and some dark areas all around you. Keep the minimum and maximum exposure times in mind. I have a small piece of paper with me with the exposure time stops so I can quickly visualize the range of the bracketing series, as seen in the picture below. Now we can closely determine wether we need 9, 7 or 5 stops shift. In our exaple you can see that between 1/15 and 1/2000 are 8 stops, so a series of 9 will do. The median exposure is one of the two values in the green box. I would choose the brighter exposure, because you will have a brighter image as extra, giving you more detail around the sun. When choosing the darker image as extra, you wil have a bit more detail in the shadow part, wich is already correctly exposed as we have tested.

 

One more thing to bare in mind now, is that you will probably have the sun itself overexposed, this will be nearly impossible to expose correctly, even with the aperture fully shut and exposure time at its shortest. When you have the area around the sun well exposed, it will do for rendering. Shoot a bracketed test sequence and check if your darkest exposure contains no pure whites (except the sun), and your lightest exposure contains no pure blacks. The histogram is the best tool for this. Check this way for the brightest and darkest direction you will shoot. If you still have pure blacks or whites, you will have to do more images. If this is not possible, consider if to clip some shadows or highlights. In the best case you shoot 2 bracketed series, but this case will be fairly rare. Delete your bracketing test sequence to avoid using the wrong pictures later on when editing. So far for the exposure settings.


Camera settings – White balance and in-camera processing

All in-camera adjustments should be left disabled, like sharpening, tone compensation, saturation and hue adjustment. This is to keep the bracketed sequence as consistent and correct as possible in color, sharpness and dynamic range. We will have more than enough editing possibilities when our stitched 32-bit HDR image is ready. When shooting RAW, you don’t have to worry about these settings, because you can change it afterwards with the correct software like Photoshop and its fabulous RAW plugin. Also, when shooting JPG the white balance is very important, at least if you want true colors. The best way to get the WB exactly right is a grey card. Hold this in front of your camera and take a picture using the cameras WB preset function. This varies with the make of camera. This sets the WB at the calculated value so the grey card is really grey in the image, and not blue or orange tinted due to WB offset.  If you don’t have a grey card, a white piece of paper will do the trick, but with less accuracy. Just be absolutely sure that the white paper is not overexposed!. It is also possible to determine a color temperature by hand. In the bright sun it will be 5500K, an overcast sky will be around 6500K, and a sunset between 2000-4000K. Always make some test shots and compare the cameras display with the real world colors and adjust if necessary, but who says the display delivers accurate, calibrated colors? So remember, if you want true accuracy, calibration and grey cards are a must!


 


Shooting the panorama

So we have our rig calibrated, our camera fully set and we are ready to go!

  • Fix your cable release if you haven’t done so already. Search your spot to take the panorama, and level the head.
  • Place an object (a stone or something you pick up from the floor) right in the center of the tripod on the ground, to mark the tripods position.
  • If you have a bright sun visible, you want to start out here, and make sure the sun is in the center of the viewfinder, this minimizes the sun flares in your optics.
  • Focus the lens, and turn off the autofocus, so it wont go shifting while we swing our cam around. Well now, let’s shoot!

 

  • Make sure you rotate just enough to get a nice overlap of 1/3 to 1/2 image. Be sure to keep an eye on your shadow so it won't get in the picture! When working with a fisheye lens, this will happen sooner as you think.
  • When you have shot all the way around, tilt your camera straight up for the zenith (top) shot.
  • Now here comes the magic: the nadir (bottom) image is a bit tricky when you want no tripod in the view. To get this nailed you will have to rotate the fixed vertical arm by 180 degrees, so the camera looks down alongside the tripod.

 

  • Move the tripod sidewards so the camera is somewhat over the center rock. Do not put the camera exactly over the rocks, but shift a little outward, so the tripod legs won't cross the legs in the second image.
  • Also mind the shadows of the tripod, put it in such a way that one tripod legs falls in the shadow of another. It leaves a 2-legged shadow, this saves you some editing time over a 3-legged shadow.
  • For the second image you have to pick up your tripod again and rotoate it 180 degrees around the center rock. Again, leave a little space between the camera and center rock and watch the shadows.


    

 

These two nadir shots can be placed over each other, to blank out the tripod in both images. I will explain this later on in the editing section. Check the image counter if you have the correct amount of images: 8 images around, 1 up and 2 down in 9-shot bracketing gives 11 x 9 = 99 images.

This way you can shoot nadir shots even on uneven surfaces. There is an easier way for the nadir, but the ground needs to be completely flat. I will not explain this, because the guys at PTgui already did a great job at it, read all about their tutorial right here.

When you are using other focal lengths as lenses, and you're not sure of how many positions to shoot, just try it out first with single images or just remind how many you would have to shoot when keeping 1/4 to 1/3 overlap in the images to rotate 360 around and overlap the first image again. Or you could always use this handy little calculator by HDR guru Christian Bloch, found here.

 

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