Film versus DSLR dynamic range

Started Jul 24, 2007 | Discussions thread
Jay Turberville Forum Pro • Posts: 12,917
Re: Bit depth and dynamic range...

You are correct when you describe how many "levels" are available to
describe shades of gray in each channel for a 12-bit bitmap image.

However this does not map directly to dynamic range. It is certainly
possible to compress the tonal values of the scene that has dynamic
range more than 11 stops into this range and still have some
measurable detail in both shadows and highlights.

Sure. It is possible. But show me one manufacturer who is doing that when they record their raw data. So far every camera I know maps the sensor tonal values in a linear fashion. So you are right that it is possible. In fact, that is exactly what is done with in-camera images that are output as JPEGs and TIFFs with 8-bit depths. But since those in-camera images start with the same 12-bit linear raw data, they also can't output more than the 11 stops.

When manufacturers start outputting raw files with non-liear tone mapping, then it will take more than a simple math analysis to understand the potential for DR. But until then, it is a perfectly good way to look at how much DR digital cameras can deliver.

There is some slight non-linearity in real life in the darkest shadows which is probably due to lens flare. That probably explains why we can actually reach and even exceed a tiny bit the theoretical DR limits. You can see that slight non-linearity in this Imatest graph. It is interesting on its own merits, but I don't think it has much relevance to practical photography with most cameras. Note the otherwise linear response.

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