- photographic equipment dynamic range:
- see also:
- this is the ability of a film or digital camera to capture a range of
image intensities that will then be translated to the range of black to
white in the final output.
- Slides have less photographic range than negatives. Slides have
perhaps about 5 or 6 f-stops of total scenic range, compared to perhaps
9 or 10 f-stops for negatives.
- the narrower the capture dynamic range, the more important accurate
- expose a slide half a stop off and the results are objectionable.
Do that with negatives, and you never even realize it.
- digital camera dynamic range:
- this is primarily determined by:
- the characteristics of the image
sensor (the results you get when shooting in RAW mode)
- number of bits A-D converter
- amount of noise produced by the sensor
- modifications by in-camera image processing (or on computer RAW
development processing) which will usually result in some loss of
dynamic range (often 1-2 EV which is usually in the highlight
- digital sensors have a linear analog output from each sensor site
such that the output voltage is proportional to the amount of
photons (light) hitting it. This analog output is then converted to
a numeric digital value via the camera's analog-digital converter
chip which then forms the "RAW" image file (although some
cameras (eg. Nikon dSLRs) have in-built processing that refines the
image file further before outputting the end RAW file.
- in digital data terms, maximum possible dynamic range of sensors
is determined by how many "bits" of data can be saved with
each image, in general, the larger the sensor, the more dynamic
- most prosumer cameras capture 9 to 10 bits which equates to
5-6 EV dynamic range (ie. equiv. to slide film)
- digital SLR's may capture:
- 8 bits (24 bits per pixel):
- each colour channel can have up to 256 values
- this is the most common final image format such as
- this is the reason you should really shoot in RAW mode
if you want to post-process your files - the limited bit
depth of 256 values will result in posterisation
artefacts if jpeg files are significantly
- cameras and RAW development software convert their
10-14bit RAW data & map it to the 256 values of an 8
bit jpeg file (see below).
- 12 bits (36 bits per pixel):
- most current digital SLR's
- equates to
approx. 8EV usable dynamic range, max. 9EV
- each colour channel can have up to 4,096 values
- 14 bits (42 bits per pixel):
- 9EV usable dynamic range, max. 10EV eg. Canon 1D
- each colour channel can have up to 16,384 values
- 16 bits (48 bits per pixel):
- this currently is only the high end digital
medium format cameras costing upwards of $A30,000 although
they may not be true 16bit range.
- each colour channel can have up to 65,536 values
- 32 bits (96 bits per pixel):
- HDR files generated from multiple exposures via HDR
- RAW image file processing:
- the RAW image file needs to be processed to derive an image
that can be viewed, this involves:
- gamma encoding correction to the desired color space (eg.
sRGB has gamma=2.2)
- de-mosaicing (Bayer array interpolation) - each photosite
on a sensor is sensitive to only one RGB colour channel and
thus the data from adjacent photosites must be interpolated
to give a 3 color channel RGB pixel.
- sharpening - although lower end cameras often over-sharpen
to give better looking small files but produce artefacts
that can be hard to remove, thus it is better to minimise
in-camera sharpening and leave it to the last step in image
- white balance adjustment
- image files and dynamic range:
- for details on tonal quality, dynamic range and digital see here
- RAW files can be converted to either 8 bit JPEG or TIFF files, or
to keep as much information as possible, to 16 bit TIFF.
- note that jpeg files are only 8 bit so you have lost range by
converting to jpeg.
- 8 bits mean that the data per color channel for each pixel can
have a value within the range of 0 to 255.
- if one uses a linear 8-bit image file (ie. gamma = 1 such that
data spread is even for each part of the exposure range) then to
fit a dynamic range of 8EV equally, each 1EV in dynamic range
would only have 256/8 = 32 possible values per channel which
would not give a sub-optimal image quality.
- Gamma encoding spreads the data and shifts the results towards
the more sensitive end of the human visual range. The stages are
first to convert the analog signal to a 10-bit or higher
internal values (depending on the hardware), then apply the
gamma function to these values, before finally rounding down to
8-bits. This preserves much of the dynamic range, and minimises
the perceptible quantisation errors in 8-bit values.
- Thus if we look at the brightest 1EV exposure zone in an
image, if it was shot in 12bit RAW using sRGB color space, this
zone would have available to it 2048 brightness levels per
channel, when this is directly converted to a 8-bit jpeg, this
same exposure zone has those 2048 levels squeezed into only 69
- If we look at the exposure zone 3 stops down from the
brightest, and thus closer to skin tones, in 12bit RAW there are
512 levels which are squeezed into only 37 levels in an 8-bit
- if we under-exposed our skin tones by 2 stops, we would have
only 128 levels in RAW which are squeezed into a measly 20
levels in jpeg with resultant marked loss of tonal range - what
could have been 512 levels of tonal range has been converted to
- THUS GENERAL RULES OF DIGITAL FOR GOOD SKIN TONAL RANGE:
- shoot in RAW mode at lowest ISO and don't under-expose.
- effect of ISO on dynamic range:
- why don't we all just shoot with camera set at ISO 100 and
under-expose as need be instead of changing the ISO upwards?
- if one assumed there was no in-camera sensor boosting
taking place, then if you double the ISO, this would equate
to under-exposing by 1EV (then boosting it by 1EV in
Photoshop to give correct exposure appearance), but the
result would be you would lose 1EV of shadow detail, and
perhaps worse if shooting in jpeg mode, due to gamma
encoding as above, you move your most important part of your
subject exposure to a lower data range which has less data
elements available for the same amount of exposure range,
thereby degrading you image.
- In actual fact, there is some sensor boosting going on
when you select a different ISO in the camera, and this
reduces the dynamic range loss from 1EV to about 0.5EV for
each doubling of EV and reduces the
- this maximum dynamic range value only applies to the ISO range
where the camera best performs at which is usually ISO 100-200.
As you increase the ISO, noise adversely impacts shadow detail
and thus the shadow region dynamic range reduces perhaps by
0.5EV for every doubling of the ISO on digital SLRs.
- dynamic range of the highlight region remains relatively
- to get maximum dynamic range, shoot in RAW mode at the
lowest ISO setting, expose correctly to avoid blown-out highlights and then select a RAW developer program and
settings that give the best dynamic range (this may include reducing
EV by 1-2 stops to capture the highlights from being blown out and
reducing the contrast setting, but color accuracy may be affected
with extreme settings).
- digital effects use of Photoshop can improve over-exposed or
under-exposed regions of an image but it cannot restore image detail
once it is lost due to insufficent dynamic range.
- to get even more dynamic range, one can bracket exposures
by +/- 2 f-stops and then combine the images to give a high dynamic
- high dynamic range (HDR) image production and tone mapping from
multiple images of differing exposures (ie. bracketed exposures such
as -2, 0, +2 stops using a tripod):
- Photomatrix or
- free basic version, but need pro version
($US99) to do tone mapping.
- may be of use to reduce noise in astrophotography
- see tutorial here
- you'll need 3 exposures (-2, 0, +2) from the camera,
adjust the light blending in photomatix, push the black up a
bit, turn micro contrast down to max, micro smoothing to
zero. push the whites a bit, the rest is up to you and the
effect you want. if the light smoothing is to the right
more, it will be more real, to the left, much less real. Use
PS to finish.
- high dynamic range
landscapes from 2 images using gradient tool in PS:
- see tutorial here
- one image exposed for the
sky, the other for the foreground
- combine as layers in PS
then add a layer mask on the over-exposed image and use the
linear gradient tool and drag the line from the top of the image
to the horizon, then adjust the opacity slider for effect
- pseudo high dynamic range from a single RAW file - suitable
for motion images but gives more noise:
Photomatix 2.2 or later
- Automate-Batch Processing select
one RAW file & hit run; need PS white balance
- photographic scene dynamic range:
- this is the EV range from the darkest shadows in which you wish to see
detail to the brightest highlights in which you wish to see detail.
- see light values and exposure
- the scene dynamic range depends on:
- subject dynamic range:
- eg. bride in white, groom in black creates an extreme subject
- lighting dynamic range:
- ie. the difference in exposure for the main light source vs
the light source lighting the shadow region.
- if you take a photo on a sunny day with the sun directly behind you so
there are no shadows, then the dynamic range will match quite well with
the cameras ability to capture it, but the lighting may not be how you
would like it.
- if you shoot with light source to the side of in a backlit situation,
then the resultant shadows will cause extreme scene dynamic range which
may need to be managed, either by:
- exposing for the highlights and let the shadows come out black
- exposing for the shadows and let the highlights come out white
- exposing somewhere in between and having black shadows and blown
- modify the scene dynamic range as below.
- if you take photos on a heavily overcast day with minimal shadowing,
the scene dynamic range may be quite small and the resultant image may
appear quite "flat" and boring
- the scene can be given contrast in a variety of ways such as:
- adding colour objects to give colour contrast
- using Photoshop to stretch the contrast so you get black
blacks and white whites, but this process may add noise.
- the scene dynamic range can be effectively modified by either:
- additional lighting or flash
to fill-in or lighten up the shadows, or,
- use of gradient &/or polariser filters
to darken bright highlights such as the sky
- use of colour filters to
modify the contrast range in B&W photography
- print or film dynamic range:
- see also:
- this is the range of optical density on a given image and becomes
important when using a scanner to copy it as the scanner ideally needs
to have sufficient image capture dynamic range to cover the image
- Image density is measured from image brightness with optical
densitometers, and ranges from 0 to 4, where 0 is pure white and 4 is
very black. More density is less brightness. Density is measured on a
logarithmic scale (similar to the Richter Scale for earthquakes).
Density of 3.0 is 10 times greater intensity than a density of 2.0.
- The minimum and maximum values of density capable of being captured by
a specific scanner are called DMin and DMax. If the scanner's DMin were
0.2 and DMax were 3.1, its Dynamic Range would be 2.9. DMax implies
unique image tone values are distinguishable, and not hidden by
- 24 bit scanners might have a dynamic range specifications near 2.4,
needed for photo prints. 30 bit scanners might be near 3.0, needed for
negatives. The best 36 bit scanners might approach 3.6, better for
- A printed magazine image has a dynamic range well less than 2.0, maybe
half of that (1.7). The blackest ink still reflects some light, the
white paper is not so bright that it blinds us, and the difference is
relatively small. Photographic color prints have a dynamic range of less
than 2.0 too. Film negatives might have a range up near 2.8. Slides may
be near 3.2. These are not precise numbers.
Dynamic range of prosumer cameras:
- consumer digital cameras tend to behave similar to color slides and
thus one should consider underexposing by 1/3 EV as one cannot retrieve
- Olympus info from George Sinesios:
- RAW files such as ORF's are stored as 16 bit files (we don't use a
12 bit file system structure; anything over 8 bits must be stored as
a 16 bit file - even though the extra bits don't contain any real or
useful information; they're just insignificant zero's).
- The C series cameras capture data as 9 or 10 bits (not 12 bits).
- No matter how many data bits are captured by a C series camera;
the image sensor is still only capable of capturing a limited
dynamic range; those 4 to 5 stops captured may be stored as 10 (or
12) significant bits, but the number of bits stored do not affect
what the image sensor is capable of capturing in the first place.
- The C series cameras are not only hampered by the limited dynamic
range directly related to the shortcomings of the image sensor; the
images are also compromised by the constant 'corrections' that the
camera's image circuits do (differently) to/for each image. The
camera's circuits 'think' we want each image to look a certain way
and then proceeds to mangle the data to give us that 'look' it
thinks we want. The result is a very 'digital' look with high
contrast and saturation and poor rendering of minute details.
- When shooting raw ORF files, a lot of the corrections the camera
does are bypassed. Shooting raw gives you the most the C series
image sensors can give: about 5 stops of usable picture information.
- BTW, the Phase One H25 22MP digital back (121 MB files) is rated
at a true 16 bit capture and a corresponding 12 stop dynamic range.
It's also listed at over $45,000 CDN so I wouldn't expect a Canon at
less than 1/10 the cost or an Olympus at less than 1/45 the cost to
compete in that stratosphere (specifically in Dynamic Range in