Dynamic Range and Raw Conversion

Having recently acquired a Canon 1DMkIII and read so much about its 14bit raw capture capability, I decided to check out what impact these extra bits had (if any) on dynamic range.

However part way through the process I noticed something quite surprising related to raw conversion, namely that different converters yield significantly different levels of dynamic range.

Using a Kodak Q13 grey-scale step chart, a whibal and a Sekonic 758 Lightmeter, I decided to capture a broad selection of manual exposures from -6EV through to +3EV of the step chart..

I then chose 3 raw images which gave me the widest dynamic range e.g. 0,0,0 through to 255,255,255 on the step chart.

Using each raw converter in turn (at default settings), I white balanced the correctly exposure image and applied this to both the under and overexposed variants. Each image was then cropped appropriately and outputted as an sRGB 16-bit tif, before being loaded into Imatest for stepchart and DR measurement.

Here are my findings:

Lightroom / ACR yielded ~8 stops

Capture One yielded ~11 stops

DPP yielded ~11 stops

SilkyPix yielded ~10 stops

Conclusion

My observations suggest that Lightroom/ACR compresses shadow detail by ~2 stops, while both Lightroom and Silkypix compress highlight detail by ~1 stop.

Only DPP and Capture One seem to offer the broadest dynamic range “out of the tin”.

Obviously, one can expand the dynamic range using functionality within any of these raw converters, however this adds time to the image editing process, especially if it’s done on an individual basis. Furthermore it’s possible that such processing would increases noise.

I suppose the key driver of this exercise was to understand what impact these raw converters have on rendering shadow and highlight detail.

My guess would be that if a raw converter provides greater dynamic range at the outset, then this would lead to better detail extraction at the DR extremes.

Before I draw any solid conclusions, my next step is to consider how raw converters address such detail extraction on real world images.

So watch this space for part two!

Until then, perhaps it’s time to re-consider what converter I use for 1DMkIII raw conversions!