Trying to break a world record is never an easy task and obviously the project we got ourselves into wasn’t easy to carry out. We knew from the start that we would have to shoot over 2000 images. Despite this fact I quickly suggested working with RAW files because of the substantial improvement the format would bring to the quality of the final JPG images we would be using for the stitching. After a bit of hesitation, we decided to take this road. Working with RAW files allowed me, when processing the 2346 individual files, to play with various optimization parameters during that first step: the white balance, noise reduction, highlight management and harmonization of the various rows and columns of source images. We knew that the actual shooting conditions were such that we would have to make some technical choices on location.
Since the shooting was taking place from a high point since we wanted to have a view of the whole city, I knew we would have one paradox to deal with: we needed a very nice sunny, clear day with good atmospheric transparency; but a sunny day means that the air would warm up. Even if we would be working very early in the morning before the sun would warm up the atmosphere too much, it would just be impossible to finish early because of the large amount of images we needed to shoot. With a 600 mm lens the atmospheric warm up would translate into turbulences that would invariably degrade image quality and sharpness when viewing them at 100%. The difference switching from a 300mm to a 600mm is striking! In order to keep this problem under control, the astronomers know that the shutter speed must be kept to the shortest possible amount. However, we needed to maintain an acceptable depth of field. I then decided on the following compromise: 800 ISO, F13 with a 600mm lens to shoot by a bright sunny day using a shutter speed of 1/800sec. Even if I was going to be using a Canon 5D Mark II I knew I would end up with some noise in the final images. I also knew that I would be able to remove it using RAW files and Photoshop’s Camera Raw. The final result is quite acceptable!
Then, always looking to keep the noise under control, I worked with a shutter speed of 1/800sec in order to slightly overexpose my shots. A speed of 1/1600 at 800 ISO would have been OK in regards of the light conditions on the day the shooting took place, but using 1/800sec allowed me to slightly darken my images in Camera Raw and recover the highlights at the same time. Finally, overexposing allowed me to adjust my white balance without modifying my files and this would have become a lot more complex if I had been working with JPG files from the start. I suggested to my partners in this adventure to develop the image with a slight warm tone so we could reunite the pictures taken in the morning with the ones taken at the end of the afternoon that had a warmer tone. Harmonizing the 17 rows and the 138 columns of images was performed quite comfortably using groups of images in Camera Raw and then synchronizing them. The slight remaining differences were processed directly during the stitching process by Autopano Giga. I am still amazed by the quality of the final harmonization. Especially when you know that the first shot was taken at 11:30 am and the last at 04:30 pm!