"Why Raw" Article
 

I have written Part I of an article titled "Why Raw". The article can
be found on my web site at:

http://ronbigelow.com/articles/raw/raw.htm


Other articles can be found on my site at:

http://ronbigelow.com/articles/articles.htm


Comments are always welcome.

Very informative.
Thank you!

"ron" wrote in message
oups.com...
I have written Part I of an article titled "Why Raw". The article can
be found on my web site at:

http://ronbigelow.com/articles/raw/raw.htm


Other articles can be found on my site at:

http://ronbigelow.com/articles/articles.htm


Comments are always welcome.

[]
"ron" wrote in message
oups.com...
I have written Part I of an article titled "Why Raw". The article can
be found on my web site at:

http://ronbigelow.com/articles/raw/raw.htm
[]
Comments are always welcome.

Ron,

There is a major error in the article, section Raw Advantage #2: Bits,
making the comparison between JPEG and RAW quite incorrect. The data in
JPEG files has a gamma correction of (typically) 2.2 applied, which means
that it can accommodate a far greater dynamic range than just 255 linear
light levels. The difference between RAW and JPEG in is the accuracy of
light level representation, not in the dynamic range.

Cheers,
David

Tnx for article, it's great. I'm reading the rest of your work...

"ron" wrote in message
oups.com...
I have written Part I of an article titled "Why Raw". The article can
be found on my web site at:

http://ronbigelow.com/articles/raw/raw.htm


Other articles can be found on my site at:

http://ronbigelow.com/articles/articles.htm


Comments are always welcome.

David,

The 255 light levels have to do with tonal range not dynamic range. The
article assumed a 5 stop dynamic range camera. That is fixed. The
camera can not exceed that. The gamma curve can make the image more
contrasty and make it appear to the eye that there is more dynamic
range. However, that will simply readjust the spread of the 255 light
levels (compressing some and spreading out others), but there will
still only be no more than 255 light levels in a JPEG file. The article
is correct.

ron wrote:
David,

The 255 light levels have to do with tonal range not dynamic range.
The article assumed a 5 stop dynamic range camera. That is fixed. The
camera can not exceed that. The gamma curve can make the image more
contrasty and make it appear to the eye that there is more dynamic
range. However, that will simply readjust the spread of the 255 light
levels (compressing some and spreading out others), but there will
still only be no more than 255 light levels in a JPEG file. The
article is correct.

The way I'm understanding it, "Figure 4: Shades vs. Stops of Light" for
JPEG is wrong. When you half the exposure, while in the RAW file the
digital value will be halved, this does not happen in JPEG. The values
would be (approximately) 255, 186, 135, 99, 72, 52 etc. The JPEG has
twenty different tonal values four stops down and five stops down from
peak white, and 69 different tonal values between peak white and one stop
down. You article gives 16 and 128 shades for these values.

David

David J Taylor wrote:

ron wrote:

David,

The 255 light levels have to do with tonal range not dynamic range.
The article assumed a 5 stop dynamic range camera. That is fixed. The
camera can not exceed that. The gamma curve can make the image more
contrasty and make it appear to the eye that there is more dynamic
range. However, that will simply readjust the spread of the 255 light
levels (compressing some and spreading out others), but there will
still only be no more than 255 light levels in a JPEG file. The
article is correct.


The way I'm understanding it, "Figure 4: Shades vs. Stops of Light" for
JPEG is wrong. When you half the exposure, while in the RAW file the
digital value will be halved, this does not happen in JPEG. The values
would be (approximately) 255, 186, 135, 99, 72, 52 etc. The JPEG has
twenty different tonal values four stops down and five stops down from
peak white, and 69 different tonal values between peak white and one stop
down. You article gives 16 and 128 shades for these values.

David



Ron:
Concerning your writeup at http://ronbigelow.com/articles/raw/raw.htm

See Figure 7 at:

Dynamic Range and Transfer Functions of Digital Images
and Comparison to Film
http://www.clarkvision.com/imagedetail/dynamicrange2

While in a jpeg file there can be no more than 255 levels, those levels
do not have to be linearly distributed. In fact they are not, just as
Figure 7 above shows. Note in that figure the dynamic range of the
jpeg and the raw file cover the same range, except for a slight increase in
noise at the low end. Of course, the 12-bit raw has more precision, and that
is the main difference between the two.


You might also check out:

Digital Camera Raw versus Jpeg Conversion Losses
http://www.clarkvision.com/imagedetail/raw.versus.jpeg1

The statements about digital camera dynamic range of the "better cameras"
have about 5 stops is incorrect. The better cameras (e.g. DSLRs) are
Poisson statistics limited (meaning photon statistics limited by the sensor's
given quantum efficiency). The sensors have over 12-bits dynamic range
and thus are limited by the 12-bit ADC. See Table 3 at:

The Signal-to-Noise of Digital Camera images
and Comparison to Film
http://www.clarkvision.com/imagedeta...gnal.to.noise/

Roger

In message ,
"David J Taylor"

wrote:

There is a major error in the article, section Raw Advantage #2: Bits,
making the comparison between JPEG and RAW quite incorrect. The data in
JPEG files has a gamma correction of (typically) 2.2 applied, which means
that it can accommodate a far greater dynamic range than just 255 linear
light levels. The difference between RAW and JPEG in is the accuracy of
light level representation, not in the dynamic range.

An 8-bit TIFF has more potential shadow detail than a 12-bit RAW file.
It is not usually realized, however, as 8-bit TIFFs generally come from
12-bit RAW files.
--


John P Sheehy

In message .com,
"ron" wrote:

David,

The 255 light levels have to do with tonal range not dynamic range. The
article assumed a 5 stop dynamic range camera. That is fixed. The
camera can not exceed that.

To say that a camera has 5 stops of dynamic range and no more assumes a
certain quality standard. With a definition that gives 5 stops for
DSLRs, you are talking about a standard of very high quality shadows.
The fact is, there is no hard, concrete limit on the dynamic range of an
image if your quality standards are flexible; the quality simply
deteriorates as you go deeper and deeper into the shadows, until noise
dominates and the signal is vague and lost in the chaos.

The gamma curve can make the image more
contrasty and make it appear to the eye that there is more dynamic
range. However, that will simply readjust the spread of the 255 light
levels (compressing some and spreading out others), but there will
still only be no more than 255 light levels in a JPEG file. The article
is correct.

A JPEG can only express 256 light levels for each color channel. Most
of the values less than about 50 only occur by demosaicing and
sharpening when they come from a 12-bit RAW file. If you took each RAW
color channel and made a bitmap from it in 8-bit gamma-adjusted space,
with no sharpening or softening applied, most of the values below 50
would not be used at all. The histogram would be spaced like this:

| | | | | | | ||||||||||||

The section to the right, where the histogram is full (without gaps) is
the range where the 12-bit RAW has more level-definition than the 8-bit
gamma-corrected space. The rightmost section has several RAW values
becoming a single 8-bit value.
--


John P Sheehy

ron wrote:

I have written Part I of an article titled "Why Raw". The article can
be found on my web site at:

http://ronbigelow.com/articles/raw/raw.htm


Other articles can be found on my site at:

http://ronbigelow.com/articles/articles.htm


Comments are always welcome.


Thanks again.

I only have one comment: It would be cool if you made your articles in
an easy to print format, like pdf. I wanted to read it this morning,
but was running a little late.... I could've printed it and read it
during my lunch break.

--
Slack