This morning we've been talking about the I/O system and how digital images are represented. Concepts as resolution and color depth must be familiar to you. But have you noticed that the quality of the pictures is not as good as your own eyes? For instance, if you're inside a room looking throw a window you can see details of the room and outside. But if you take a photograph you can't see both (inside & outside). You have to configure your shot for one of these scences. That's because the 24 bits of RGB are not enough to represent all the shades os the real world. For doing that a new technique apeared in the middle 90s: the High Dynamic Range Imaging or HDRI.
It's based on the representation of the luminance of the real world. Basically, if you eliminate the information about the color, information about the intensity of the light is all what you get. Remember a 256-grey scale picture; it just represents 256 different values of light, whereas the human eye can distinguish between 10.000 different values or so. That's why we can see things that a camera can't take.
How can we solve that? Well, the HDR format use high definition pictures by increasing the number of bits to represent each colour. So we can use 8-bit pictures (8 bits for each component -RGB model-), 16-bit pictures (48-bits per pixel in total) or 32-bit pixels (96 bits per pixel). Only the last one are considered High Dynamic Range Pictures.
Ok, I've understood it. But now... how can I take this photographs? Because I can't change the bits of my camera. It stores the picture in a JPEG file, using 8-bit images. Well, yes, that's true. But there is a way to do that. Just follow these advices, the post How to Create Professional HDR Pictures, from Backing Winds or this tutorial of HDR in Photoshop.
Some interesting links are
- Notes on the Resolution and Other Details of the Human Eye
- Photomatrix, software to merge common shots into a HDR picture
- New York City at night (3024 x 1998, 3Mb)
- John Miles HDR Gallery
- Flickr group for HDR.
(Picture source: Paulo Barcellos Jr., from the Wikipedia)