dSLR dynamic range question

Question: from what I understand, RAW files have more dynamic range than
JPEG files, i.e. one can choose some slight "exposure compensation" (+/-
0.5, maybe +/- 1 stop) when going from RAW to JPEG. Now, if this
information is in there anyway, why can't it be displayed in jpeg??? I
read of people making 2 JPEGs, from the same RAW file, one under and one
over-"exposed" and then blending them in Photoshop. Why can't the RAW
converter do that, i.e. extract the entire dynamic range from a file???

chibitul wrote:
Question: from what I understand, RAW files have more dynamic range than
JPEG files, i.e. one can choose some slight "exposure compensation" (+/-
0.5, maybe +/- 1 stop) when going from RAW to JPEG. Now, if this
information is in there anyway, why can't it be displayed in jpeg??? I
read of people making 2 JPEGs, from the same RAW file, one under and one
over-"exposed" and then blending them in Photoshop. Why can't the RAW
converter do that, i.e. extract the entire dynamic range from a file???

Yes, the full dynamic range is preserved in the raw file.
If one converts the raw to 16-bit output, e.g. a 16-bit tif,
then one can process in one file the full precision dynamic range.

Note that the jpeg is 8-bit (256 levels) whereas raw is 12-bit
(4096 levels), or 14-bit (16,384 levels). The jpeg 256 levels
can be spread out over the same dynamic range as the 12 or 14 bit
raw, just that there is not the fine intensity detail. The jpeg
conversion is not linear either, but follows a transfer curve
similar to film, with less intensity detail in the shadows and
highlights. A raw file can usually be used to extract subtle
information in the shadows and highlights, if processed in
16-bit mode. To extract 2 jpegs, a high level and a low
is just extra work in my opinion. Older versions
of photoshop had less 16-bit ability so perhaps it was
needed, but not with modern software. Note you must effectively
compress the intensity range for display anyway as no screen
or print medium has much more than 8-bits of range. Depending on the
scene, a jpeg, if exposed well, may be adequate. I shoot both
jpeg and raw files, depending on the situation.

Roger Clark
photos, digital info at: http://www.clarkvision.com

In article ,
"Roger N. Clark (change username to rnclark)"
wrote:
[snip]
A raw file can usually be used to extract subtle
information in the shadows and highlights, if processed in
16-bit mode. To extract 2 jpegs, a high level and a low
is just extra work in my opinion. Older versions
of photoshop had less 16-bit ability so perhaps it was
needed, but not with modern software. Note you must effectively
compress the intensity range for display anyway as no screen
or print medium has much more than 8-bits of range. Depending on the
scene, a jpeg, if exposed well, may be adequate. I shoot both
jpeg and raw files, depending on the situation.

Thanks for your comments; i had some trouble with shadows myself, next
time i will try to shoot RAW as well as jpeg.

In article ,
"Roger N. Clark (change username to rnclark)"
wrote:
[snip]
A raw file can usually be used to extract subtle
information in the shadows and highlights, if processed in
16-bit mode. To extract 2 jpegs, a high level and a low
is just extra work in my opinion. Older versions
of photoshop had less 16-bit ability so perhaps it was
needed, but not with modern software. Note you must effectively
compress the intensity range for display anyway as no screen
or print medium has much more than 8-bits of range. Depending on the
scene, a jpeg, if exposed well, may be adequate. I shoot both
jpeg and raw files, depending on the situation.

Thanks for your comments; i had some trouble with shadows myself, next
time i will try to shoot RAW as well as jpeg.

Very interesting comments.

One further comment: The resolution of each ccd sensor is unlikely to
be able to resolve anything like 16 bits which is probably why the
manufacturers limit the raw resolution to 12 bits. At higher ISOs
the resolution is 'swamped' by noise so there is no point in attempting
to preserve all 12 bits.

Graham


"Roger N. Clark (change username to rnclark)"
Yes, the full dynamic range is preserved in the raw file.
If one converts the raw to 16-bit output, e.g. a 16-bit tif,
then one can process in one file the full precision dynamic range.

Note that the jpeg is 8-bit (256 levels) whereas raw is 12-bit
(4096 levels), or 14-bit (16,384 levels). The jpeg 256 levels
can be spread out over the same dynamic range as the 12 or 14 bit
raw, just that there is not the fine intensity detail. The jpeg
conversion is not linear either, but follows a transfer curve
similar to film, with less intensity detail in the shadows and
highlights. A raw file can usually be used to extract subtle
information in the shadows and highlights, if processed in
16-bit mode. To extract 2 jpegs, a high level and a low
is just extra work in my opinion. Older versions
of photoshop had less 16-bit ability so perhaps it was
needed, but not with modern software. Note you must effectively
compress the intensity range for display anyway as no screen
or print medium has much more than 8-bits of range. Depending on the
scene, a jpeg, if exposed well, may be adequate. I shoot both
jpeg and raw files, depending on the situation.

Roger Clark
photos, digital info at: http://www.clarkvision.com

Very interesting comments.

One further comment: The resolution of each ccd sensor is unlikely to
be able to resolve anything like 16 bits which is probably why the
manufacturers limit the raw resolution to 12 bits. At higher ISOs
the resolution is 'swamped' by noise so there is no point in attempting
to preserve all 12 bits.

Graham


"Roger N. Clark (change username to rnclark)"
Yes, the full dynamic range is preserved in the raw file.
If one converts the raw to 16-bit output, e.g. a 16-bit tif,
then one can process in one file the full precision dynamic range.

Note that the jpeg is 8-bit (256 levels) whereas raw is 12-bit
(4096 levels), or 14-bit (16,384 levels). The jpeg 256 levels
can be spread out over the same dynamic range as the 12 or 14 bit
raw, just that there is not the fine intensity detail. The jpeg
conversion is not linear either, but follows a transfer curve
similar to film, with less intensity detail in the shadows and
highlights. A raw file can usually be used to extract subtle
information in the shadows and highlights, if processed in
16-bit mode. To extract 2 jpegs, a high level and a low
is just extra work in my opinion. Older versions
of photoshop had less 16-bit ability so perhaps it was
needed, but not with modern software. Note you must effectively
compress the intensity range for display anyway as no screen
or print medium has much more than 8-bits of range. Depending on the
scene, a jpeg, if exposed well, may be adequate. I shoot both
jpeg and raw files, depending on the situation.

Roger Clark
photos, digital info at: http://www.clarkvision.com

"Roger N. Clark (change username to rnclark)"
wrote in message ...
SNIP
Note that the jpeg is 8-bit (256 levels) whereas raw is
12-bit (4096 levels), or 14-bit (16,384 levels).

True, but do note that the JPEG is 8-bit after gamma adjustment, and
the Raw data is before gamma adjustment. Also, there is probably 1.5
bits of noise in the Raw data (ADC + quantization).

Bart

"Roger N. Clark (change username to rnclark)"
wrote in message ...
SNIP
Note that the jpeg is 8-bit (256 levels) whereas raw is
12-bit (4096 levels), or 14-bit (16,384 levels).

True, but do note that the JPEG is 8-bit after gamma adjustment, and
the Raw data is before gamma adjustment. Also, there is probably 1.5
bits of noise in the Raw data (ADC + quantization).

Bart

"Roger N. Clark (change username to rnclark)"
wrote in message ...
SNIP
Note that the jpeg is 8-bit (256 levels) whereas raw is
12-bit (4096 levels), or 14-bit (16,384 levels).

True, but do note that the JPEG is 8-bit after gamma adjustment, and
the Raw data is before gamma adjustment. Also, there is probably 1.5
bits of noise in the Raw data (ADC + quantization).

Bart

Bart van der Wolf wrote:
"Roger N. Clark (change username to rnclark)"
wrote in message ...
SNIP

Note that the jpeg is 8-bit (256 levels) whereas raw is
12-bit (4096 levels), or 14-bit (16,384 levels).


True, but do note that the JPEG is 8-bit after gamma adjustment, and
the Raw data is before gamma adjustment. Also, there is probably 1.5
bits of noise in the Raw data (ADC + quantization).

Bart

Bart,
Yes, that is what I meant when I said
"The jpeg conversion is not linear either, but
follows a transfer curve similar to film..."

Roger