Format of High-Dynamic Range (HDR) images and how to process them?

Question

I have some questions regarding High-Dynamic Range (HDR) images. First, can somebody please tell me about how these images are stored, I mean in which format? and how many bits per pixel?

Second, is it possible to store these kind of images in a commonly used image formats, like PNG, TIFF etc, with 8 bits per pixel (per channel)?

Actually, I want to compare images from a commercial camera and from a HDR camera. So, it would be ideal for me, if they are in the same format with same number of bits per pixel. I intend to use OpenCV for image processing algorithms.

Thanks a lot.

Answer 1

HDR images are usually composed using several "normal" images captured with varying exposures. There are cameras and softwares that do this automatically, but it can also be done manually by choosing different images and regions. For example, this can be done using GIMP.

The format used to store images is entirely up to the camera, the software or the user respectively. Some formats store all the input images and the composite image, while others simply create a single composite image and store that. So yes, you can have an HDR image stored in a commonly used format.

With respect to what you're trying to do, it will definitely be possible to use OpenCV to create an HDR image and store it off in the same format as your camera does.

Answer 2

It depends on the format, camera and/or software tool you are using.

HDR is a technique/method, not an image format; so yes, for average use, an HDR image can be stored in any format (of course, once saved (rendered), the HDR properties such as the tone map cannot be changed). If you want to dig deeper, OpeneXR is an open source format for industrial-level HDR imaging that even offers 32bit channels.

Also, you can produce HDR images with virtually any commercial/consumer camera, that has manual settings. So the input image color depth depends on your input images - 8bit for JPEG and 10-14bit for raw formats, such as NEF, CR2, PEF, etc.