70D Dynamic Range is actually great, despite what DXOMark says

Started Jan 21, 2014 | Discussions thread
David Hull
David Hull Veteran Member • Posts: 6,388
Re: 70D Dynamic Range is actually great, despite what DXOMark says

TTMartin wrote:

Sid911 wrote:

Apologies for noobie question, do all the Canon APS-C sensors display the same dynamic range? What I am really trying to find out is, from just the DR perspective, would Canon 70D be similar to say, a T4i or T3i?

According to DxOMark every Canon dSLR they have tested basically has the same per pixel dynamic range. That includes the original 2003 APS-C Digital Rebel and the full frame 1D X. Any changes in dynamic range scores is because DxOMark uses a formula that changes the print dynamic range score based on the number of megapixels.

So you can choose to believe DxOMark, or you can look at possible flaws that would explain these seemingly erroneous results.

There is a group here that believe the results are accurate and can be explained by noise from the external analog to digital converter, I don't believe this is correct.

First DxOMark attempts to measure sensor noise by looking at the RAW file. This basic concept is inaccurate because manufactures can apply different amounts noise reduction prior to the RAW file being written. Case in point the Nikon D300, Nikon D300s, and the Nikon D90 all use the same sensor. Yet the Nikon D90 scores higher than the Nikon D300 and Nikon D300s, because the D90 applies more noise reduction PRIOR to the RAW file being written.

Camera that use Sony sensors apply noise reduction at the sensor level prior to the RAW file being written.

Canon embeds information in the RAW file to be used by their RAW converter DPP. Third party RAW converters don't take advantage of this information. For example Canon masks portions of the edge of their sensor, to provide information on both row and column sensor noise, 3rd party RAW converters like the one used by DxOMark do not use this information.

Third party RAW converters attempt to directly read portions of the Canon CR2 file and directly convert them to RGB. There are several problems with this, first according to Canon's Chuck Westfall Canon RAW data is recorded in sYCC and not RGB.

So the process of direct conversion to RGB often result in unexpected results, like this CR2 image from my Canon 6D with a 3rd party RAW converter that doesn't know the 6D exists.

Another flaw in this attempted direct conversion to RGB is that it uses the HSB/HSV color space instead of the HSL color space used by Canon.

So what does all this actually mean. In my opinion the Canon CR2 file has been incorrectly reverse engineered by 3rd party RAW converters. This incorrect reverse engineering has only resulted in 12 bits of usable data per pixel and not the full 14 bits. And it is this that actually explains why testing sites that use 3rd party RAW converters show that Canon's per pixel dynamic range has remained unchanged in the last 10 years and not that the 2003 Digital Rebel and the Canon 1D X have the same per pixel dynamic range.

DxO doesn't tell the whole story though.  The real issue is the pattern noise which they don't even report.  The 70D is a good performer in that regard.  Hopefully Canon won't loose the recipe for future designs.

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