这个人说的对不对？# PhotoGear - 摄影器材
t*k
1 楼
http://www.dpreview.com/forums/thread/3611126
Re: 70D Dynamic Range is actually great, despite what DXOMark says
In reply to Sid911, 7 months ago
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.
View: original size
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.
View: original size
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.
No EXIF data.
View: original size
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.
Re: 70D Dynamic Range is actually great, despite what DXOMark says
In reply to Sid911, 7 months ago
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.
View: original size
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.
View: original size
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.
No EXIF data.
View: original size
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.
