Reduce HDR sky noise

Often while shooting for HDR at night or in the afternoon when the light is low there is an unpleasant side effect. The sky (if present) is extremely noisy. Case in point (click for large version):


(Note that in this picture I applied an unsharp mask to enhance the details on the building because tone mapping tends to create blurry results, and so the noise is a bit exaggerated but the scene was pretty noisy even without the unsharp mask)

To fix the sky noise I came up with a pretty simple solution. I choose one of the three original exposures for the HDR :


I chose the most exposed frame so that I will have the most well lit sky. I then select the sky only, by selecting a color range, selecting the sky and setting my fuzziness to a satisfactory level :


I then copy the sky and paste into a new layer over my HDR. This is the result :


The result is already looking good but it has one drawback. The overlay also darkened the shadow places of the HDR. This can be fixed by simply erasing the parts of the overlay you don't want (keep only the noisy parts in). These are the original and final version of the overlay (white parts are transparent) :



Finally here is my final HDR with the final sky overlay.

Time Lapse Photography

First post in along time. What was the cause? This. I recently purchased this remote control for my camera which i highly recommend. It's cheap and has very neat features. Two downsides only : First, it is not wireless but i can i live with that. Second the minimum exposure time you can set for your camera from the remote is 1'. You can of course use the camera setting and override the setting on the remote but when you want to take different exposure steps and it's daylight you cannot adjust the shutter time to the ones you need without handling the camera (and thus moving it).

The main reason i bought it though was the time lapse capabilities. As a first test i shot a simple view of the sky.

The process you want to follow is easy. Determine first of all the time frame for your animation. You might for instance want to shoot 12 hours of a day from dusk till dawn. Once you figure out this time frame you calculate the amount of seconds it contains. For the example i gave you it's 12 hours * 60 minutes (per hour) * 60 seconds (per minute) = 43200 seconds.

After that you need to determine how long you want your video to last. Let's say you want your video clip to last 2 minutes. Again you figure out the seconds in that period. In this case 2 minutes * 60 seconds = 120 seconds.

Lastly you need to figure out the frame rate of your video. In the States that's usually 30fps while in Europe it's 25fps. Of course you can choose whatever you wish. You can have extra fast or even extra slow frame rates. Let's go with 25 for this example.

So our video will consist of 25 frames/second * 120 seconds = 3000 frames.

Now that we know how many frames we are going to shoot and the time frame for those we can calculate how often a new frame must be photographed. Thats 43200 seconds / 3000 frames = 14.4 seconds.

That means that we must set our remote to take a new picture every 14.4 seconds (unfortunately the model i bought only has a setting for integer values and so i would have to choose between 14 and 15 seconds which would yield similar results)

You then set your exposure and start taking pictures. Note that you have to set your camera to manual mode and adjust the settings correctly.

One last note about shooting time lapse at night. I tried shooting the stars . In the very dark conditions when i shot it, i realized that each frame had to be exposed for 30 seconds to get a bright enough result. So in this case the exposure time for each frame will dictate your other settings (such as how often you will shoot new frames and how long the animation will last).

The last step is to compile a video. You can use a lot of different programs (some free some not. Google and you'll find many) but for my very simple first attempts i used Picasa 3 which has a time lapse feature. The main reason i used that was that i had it installed, it is easy and i was bored to install another program. The only downside is the .wmv files it produces :D

These are my first results :