Monday, April 9, 2012

HDR Panoramas

So I was staying up in Perth last night and this morning after breakfast we headed out for a walk and that took us up to Kinnoull Hill. On top of the hill over looking the Tay Valley is a Victorian folly. I'd seen this the day before and wondered what the view would be like from up there. A folley, I was later to learn, is a fake or decorative building that the Victorians would erect to give the area a bit more style and kudos. They usually served no other purpose other than to raise the profile of the resident gentry so that they could boast about castles on their land etc. Anyway, the issue today was that I didn't have my wide angle lens with me. This presented a problem - how was I going to get everything in shot? Also my wide angle has a 77mm filter and these don't fit my other lenses to I was a bit screwed if the sky was going to be very bright. Yes there are other ways round this but I decided to employ some other techniques and see if I could get something decent. Firstly, I decided I wanted a panorama. That meant taking a series of shots from the left hand side of the view through to the right and then stitching them together in photoshop afterwards. But as I said, I didn't have any filters that would fit the lens that I was using so I decided to employ that old love/hate technique of HDR. So here are the first set of shots. 4 portrait orientation shots each of which were made up with 5 different exposures. The dark shots catch the highlights and the bright ones pick up the detail in the dark areas. Merge these together and you get a shot that has detail every where. Below are the 4 shots before the merger.
So that bit above is called tonemapping and I use Photomatix to do this normally. Once in photoshop, I went to "new" and then opened a "photomerge" file. You then take the shots you want and add them to the open window then merge the files. I just used the auto settings and it turned ou quite well. So below is the result of this.
Ok, so the above shot is ok but there is a few things that don't look right. Mainly the colour and the contrast are a bit off so there are plenty of things that can be tinkered with in photoshop. I tend to boost the colour a wee bit and then use a lot of dodge and burn manually to pick out some more detail. Also a bit of vignette helps at this point too. This is a bit of a rush job as I'm back at "real" work tomorrow but I wanted to get this post up.
So the next thing I noticed about the above picture is that when you look at it closely there are some real issues. These mainly come from the fact that each of the shots in the pre-photomerge are a series of several shots. Therefore to take these the camera fires off 3 or 5 or 7 or 9 snaps (depending on how it's set up) in a row at different exposures. During the time it takes to take these shots things move! This is all well and good if you are taking an HDR shot of a building or something static. However, these pictures had moving cars and branches etc in them. This means that each of the 5 shots that I used to build each of the HDRs for the above panorama has slight "ghosting" effects. Up close the branches look a bit blurry or there are trails of cars (usually grey) along the road. Photomatix does a decent job of removing these but it can't deal with all of them. So is there an option to fix this? Yes. Some people spend hours and hours cloning out all the problem bits which essentially erases them from the picture. But as I said this can take a long time. It does give a good result and if you have a lot of time then this is a decent way to go. However, there is another way round this and it's by doing what's called a "pseudo-HDR". The difference with this technique is that you only take one shot instead of a whole series of shots. You then use the RAW file to create an underexposed jpeg, a normally exposed jpeg and an overexposed jpeg - hence three different exposures from a single photograph. This means that these are all identical shots so there are no waving branches and moving cars etc. I did this with three different shots the same way I did the panoramas above (but from a slightly different location) and then dealt with them the same way as the "proper" HDR shots. This is the result and you can see that it's not that different from the second shot in this post. Decent result from only 3 photographs in comparison from the 20 that were used to create the first panorama.
Don't worry, this post is almost at an end. After a few tweaks in Photoshop here is the final result and I think that this might be the way forward for HDR when there are moving objects are involved. I know there are some real masters out there that don't need this in their trick bag but I think I do mainly because it takes me so long to do a normal HDR. Anyway, hope this jibberish all makes sense and if you've got any question then please leave a comment and I'll do my best to answer it.
Who needs a wide angle lens??? Get snappin! Z

1 comment:

  1. I went out oday to try this but have not got a straight horizon-too much curvature from the wide angle lens.

    What focal length did you take this at?