Neat Image user guide / Filtration
process details / Stage
III. Adjust filter settings
Adjust filter settings (Advanced mode)
As compared with the Standard mode (see the Adjust
filter settings (Standard mode) subsection), the Advanced
mode offers a more sophisticated sets of filter controls. There are also
two main filters - noise reduction filter and sharpening filter - but these
have more adjustable settings now. Please follow the guidelines below to enable
/ disable and adjust both filters.
Adjusting noise filter settings in Advanced mode
In the Advanced
mode, the noise filter has separate settings for all frequency
and channel components of the input image. There are pairs of noise
level - noise reduction amount controls for each of these image components.
The meaning of each noise level - noise reduction amount
pair is the same as explained in the Adjusting
noise filter settings in Standard mode: a noise level control determines
which image elements are considered noise in corresponding image component;
a noise reduction amount control determines how much reduction is applied to
the image elements identified as noise.
Because the noise level controls are relative to the device noise profile,
their defaults usually produce good results. The noise level defaults are 0%
(some of the noise level defaults may be different from 0%), which means the
noise levels are completely determined by the noise profile. When the level
controls are set differently, the noise level estimations are raised or lowered
accordingly. A noise level can be in the range from -100%, which means no image
elements are considered noise, and therefore, no noise reduction is applied
in the corresponding image component; to +150%, which means noise reduction
is applied to the image elements that are weaker than 250% of the noise profile's
noise level.
Noise reduction amounts can be in the range from 0% (none of the detected noise
is removed) to 100% (all the detected noise is removed). By default, the noise
filter removes 100% of detected noise (some of the noise reduction amount defaults
may be different from 100%).
Decreasing the noise reduction amounts can have a positive effect if the input
image contains some natural noise. For example, when you filter images of asphalt,
sand, or anything else that contains fine natural noise-like features, it may
be helpful to reduce amounts down to 40-50% (see Partial
filtration for additional tips). Our experience shows that these values
generally provide a good balance between preserving image details and noise
removal.
It is recommended to disable the sharpening filter when adjusting the noise
filter. To disable the sharpening filter, uncheck all channels in the Sharpening
Settings box.
Adjust noise reduction amounts (optional)
- Use the Noise Reduction Amounts: High, Mid,
and Low; Y, Cr,
Cb (R, G,
B) sliders.
You can vary the noise reduction amount for each frequency and channel component
of the input image. The higher a specific noise reduction amount, the more
of the detected noise is removed in the corresponding image component. Be
careful, setting the noise reduction amounts too high can lead to loss of
fine details and unnaturally looking (over-smooth, plastic-like)
results. Too low amounts may be not enough to sufficiently remove the objectionable
part of the noise. You have to balance the noise reduction amounts (most importantly,
the amount of noise reduction in the Y channel) to
get the result that looks best to your eyes.
Comment |
As human vision is not very sensitive to variations
of colors, strong filtration in the Cr and Cb channels does not noticeably
distort an image, but efficiently removes color noise. |
If the input image has only fine (high frequency) noise elements you can utilize
only the high frequency filter and switch off the filters for other frequencies
by setting their amounts to 0%.
Noise samples of different frequency/size are shown
in the Noise Filter Settings box. These are
examples of grainy structures typically regarded as noise. |
 |
Adjust additional filter settings (optional)
- If the input image contains strong low frequency noise then you may want
to switch on the very low frequency filter (check the Very
low freq checkbox in the Noise Filter Settings
box).
Smooth edges
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Off
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On
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- Check the Smooth edges checkbox to make edges
and lines look smoother (see an example on the right).
- Check the High quality checkbox to enable higher
quality noise reduction filter. This will slightly slow down processing but
will deliver the most accurate results in return. You may want to check this
option in the very end just before applying the filtration to the whole image.
- Check the High resolution checkbox to enable the
higher resolution noise filter. This may be useful when processing images
with very fine details that should be better preserved by the filter.
Use preview
- Use the preview when adjusting the noise filter settings.
After you have made changes to the noise filter parameters, do not forget
to check the preview. Use the preview on different parts of the image to get
a better feeling for the results of noise reduction. Using the Auto
recalculate preview option is recommended (see Filtration
options).
If the noise filtration looks too strong (weak) try to decrease (increase)
the noise reduction amounts for appropriate channels and/or frequency ranges.
Usually it is not necessary to change the noise levels if the noise profile
is accurate. You only have to adjust the noise levels if you see that some
noise elements are not reduced even if you set the noise reduction amounts
to 100%. Such residual noise elements are caused by inaccurate noise profile
(providing inaccurate noise levels). This may be compensated by adjusting
(increasing) the noise levels in the filter settings.
Adjust noise levels (optional)
- Use the Noise Levels: High, Mid,
and Low; Y, Cr,
Cb (R, G,
B) sliders.
The noise filter has access to three frequency components and three channel
components of the input image. Corresponding sliders adjust the estimated
noise levels for each of these components.
The higher a specific noise level, the more image elements in the corresponding
image component are considered noise. Be careful, setting a noise level setting
too high can lead to removal of important image details. Setting a noise level
setting too low can lead to incomplete filtration: residual noise and compression
artifacts can stay in the output image.
As a rule, if the device noise profile has been built properly, it is not
necessary to increase the noise levels by more than 50%. If the input image
contains strong surges of noise in the high frequency range, it is recommended
to increase the high frequency noise level up to +20 to 40%.
If the input image contains strong color noise, it is recommended to increase
the Cr and Cb noise levels to +30%. In some cases, it may be useful to increase
these noise levels up to +100%.
If adjusting noise levels still does not help and some noise elements remain
in the image, probably the device noise profile is not good at all. Return
to Stage II. Prepare a device
noise profile and additionally fine-tune the device noise profile or simply
rebuild the profile from scratch.
Use Component Viewer (optional)
The Component Viewer is intended for detailed examination
of both frequency and channel components of the image. Find more details about
using this tool in the Component
Viewer subsection.
Use Variant Selector (optional)
The Variant Selector is designed to compare several
variants of filtration side-by-side to find the optimum filter settings easier
and faster. More information about this tool is available in the Variant
Selector subsection.
Adjusting sharpening settings in Advanced mode (optional)
Note: You can skip this subsection when reading for the first time.
The sharpening filter is designed to increase image sharpness without increasing
the noise strength.
The default values of the sharpening settings should produce satisfactory results
(when sharpening is enabled for any of the channel components) but you are encouraged
to vary the settings to find values that produce the desired level of sharpness.
Zero sharpening amounts will not sharpen the image at all. The non-zero sharpening
amounts will apply sharpening of the specified strength. Use sharpening controls
for different frequency components to sharpen fine, medium or large image details.
As with any other sharpening method, you have to balance the amounts to avoid
over-sharpening.
Use the preview when adjusting the sharpening settings.
Select color channels where sharpening should be applied
Use checkboxes
in the Sharpening Settings box.
If the working color space is RGB, then all color channels should typically
be processed. If it is the YCrCb color space (JPEG or Symmetric), then, usually,
there is no need to sharpen the Cr and Cb channels.
Select sharpening mode
- Check the Conservative checkbox to enable more
accurate sharpening, which produces much less halo effect around sharpened
image details.
Adjust sharpening amounts
- Use the High, Mid and
Low sliders in the Sharpening Settings
box.
Specify how much sharpening should be applied to each frequency component
of the image.
The standard sharpening settings used by many graphic editors are 100% for
high frequency and 0% for medium and low frequencies (used by default).
Use preview
- Use the preview when adjusting the sharpening settings.
After you have made changes to the sharpening settings, do not forget to check
the preview. Use the preview on different parts of the image to get a better
feeling for the results of sharpening.
As soon as you are happy with the preview results regarding both noise reduction
and sharpening, proceed to the subsection about saving
the filter settings into a preset or to the Stage
IV. Apply filter to the input image.