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HDR on the iOS 4.1
I was looking at the Keynote from Steve Jobs at the Apple Special Event celebrated this 1st of September. And one thing that interested me was the new ability for the iOS 4.1 in the iPhone and the new iPod touches with camera (event next generation iPads that is rumored to have camera….) to take HDR pictures.
I don’t know if to get excited or not… In one hand I’ve been taking HDR pictures and Tonemapping them for some time, I know a thing or two even-though I’m no pro. I’ve also developed a VFX oriented application called LIG3D for my undergraduate Thesis that works with HDR images. There is a general misconcept about HDR images.
First of all what is an HDR image?
Well, the easy way to explain, this is with an example:
As you can see this are three pictures of the same space captured with different exposures. The picture in the middle has an exposure od +0.0 and has some detail but the parts ont the left and right of the picture are a little two dark and also the interior is a bit blown up. (I know it’s really small). An HDR image combines a Dynamic Range of light captured in a single image so all the light and color information are available in one photo. It can be created from multiple exposed images or with special cameras.
The problem is that HDR images can be displayed in a Low Dynamic Range (LDR) display such as a normal computer screen or a mobile device screen. So there are techniques of “faking” the display of HDR images and it’s called Tonemapping.
This capture shows this proces called tonemapping and you can see all parts of the picture well illuminated. This is not an HDR image. It’s a Tonemapped HDR image. A real HDR image is a 32-bit image normally wit extensions such as .hdr .exr etc. In a normal display they look like a normal picture. If you open it in a HDR ready program you can tweak the exposure and see the whole dynamic range of light in the image.
So what does the iPhone do?
The iPhone (for what I’ve seen in the keynote) takes 3 exposures of your photo and combines them with some tonemapping algorithm giving you a tonemapped HDR image. A little like the one you see up above. So if you take a picture of you girlfriend with a great sunset on the back, you’ll get the sunset and your girlfriend in the foreground. (Although I’m a little scheptic about the quality of the tonemapping algorithm because tonemapping is almost an art and leaving everything by default doesn’t give you always a good result.)
Is this good or bad?
It’s good in a way that it’s going to get out to the mainstream. HDR photography has been around for a long time. Gustave Le Gray already had in mind the problem of fixing over or under exposed photographs in the 1850’s! He combined different exposed captures to create the first set of “HDR” images. I just say this so nobody claims that Apple has invented this concept like what happened with FaceTime.But we all know that some things are thrown out to the mainstream that the mainstream isn’t prepared to assimilate or that it’s just going to give a misunderstood of what HDR is really about. Because as I said before, tonemapping an image is not easy to get a good result. So leaving it all in the hands of the phone will give some bad results and people will begin to wonder if this really works…
We’ll see how it goes. And I’ll try it myself to see what it really is about.
Finally if you want to see some of my HDR work head on to:
