For holiday I’ve been to the North Sea this year and of course, like anybody else there too, I had to take a sunset picture. However, I didn’t want it to be too easy. Therefore I took two series of pictures with multiple exposure (-1, 0, 1 EV), which overlapped approximately by half. I do not own a high quality DLR camera, just a good compact camera. In the following I will describe, what I did to create a panorama of these pictures and which problems I experienced. Here are the initial pictures of the sunset:
Combining the multiple exposed pictures
First of all I created the HDR pictures with Luminance HDR. When you create a new HDR picture you are prompted for the pictures and have the options to “Autoalign images” and “Auto-crop” them, which is a good choice if you take the pictures without a tripod like me. I followed more or less the description given here to create the HDR pictures and will briefly describe it:
After the alignment finished, I chose “profile 5” and created three different HDR pictures.
- I immediately saved the HDR image preview (“Save HDR image preview” option in the File menu). You can see the picture in the first column/row below.
- The next picture is with the Ashikhmin algorithm with equation 4 and “Local contrast Threshold” set to 0 (second column).
- The last picture is the default Mantiuk ’06 algorithm (last column)
I repeated this for the second series of pictures (second row).
Next step is combining these three pictures. As you can see above some algorithms are good in capturing the contrast, but are bad in capturing the colors and vice versa. For the further image manipulation I use Gimp. I overlayed the “preview” image with the Ashikhmin” with 80% opacity in Mode “Multiply” and on top with the “Mantiuk ’06” picture at 30% opacity also in multiply mode. Then I flattened the image and went on to create the panorama.
I used Hugin to create the panorama. Since all the camera meta data was lost in the meantime I had to get the “Focal length” and its “multiplier” from one of the original pictures and filled it in by hand, when the pictures were loaded. Then I could let Hugin do all the job and ended up with the following picture:
That looks odd! There are two hills in the flat ocean! That must have something to do with my camera. So far I created panorama pictures only in rough terrain, but never where the horizon should be absolutely flat. Therefore I had to use Gimp again to straighten the horizon. The filter “Lens distortion” in the “Distorts” sub-menu did the job sufficiently. I adjusted the “Main” and “Zoom” values until the horizon was slightly bent to the other direction and I had the following pictures:
And I ended up with this beautiful HDR panorama picture:
That’s almost perfect! The horizon is not yet absolutely straight, but taking into account that this was relatively quick the result looks sufficient. And of course it can never replace viewing the original sunset.