Here is
my understand regarding Calibration, Negafix and Color Cast Removal.
Calibration
Calibration serves to match the colour data received from the scanner with known colour data. It does not perform any colour balancing, mask removal or color cast removal. It ensures that the scan data after digital mapping is as true a representation of the
film as possible.
While some people may disagree, I believe that calibration should be independent of Negafix, producing accurate scan data which would include the orange mask if present. Negafix could then be applied to accurate calibrated scan data. If possible, I would prefer to use SF Ai to produce calibrated HDR scans of negative film, and then use SF HDR's Negafix to extract the orange mask and invert the image.
In my mind, turning on
ColorSync for
Scanner > Internal is equal to turning on IT-8 Calibration
only if the corresponding scanner profile is accurate. If the scanner profile is a generic profile for the scanner model, turning on ColorSync does not represent an
accurate CMS workflow; just an
automated workflow. Beggars (such as myself) cannot be choosers though and using a generic profile is probably better than not using any profile at all.
(In case any other Super Coolscan 4000 ED owners are interested, I was able to produce SilverFast-recognised generic icc profiles for the scanner from the Nikon-provided profiles for 14-bit and 8-bit scanning using a HEX editor to replace the 4-character profile type code. If anyone would like to know how to produce the profiles, please send me a Private Message.)
Calibration result:
Accurate scan data.NegafixNegafix is the foundation of getting true (ie, accurate, precise, faithful) scans from Negative film.
Negafix's only purpose is to effectively extract the negative film's 'orange mask' from the image data
before inversion.
Once the mask has been extracted, the image data should be the equivalent of what we would see if we developed a photograph from the film using conventional projection methods. This means that all colour casts caused by light temperature variables should be retained within the image. Only then would we have a
true image.
For the average user, standard Negafix should be sufficiently accurate to produce acceptable images. ('should' would be true if the profiles were accurate which unfortunately is not true for many of the profiles provided with SF Ai NikonM.) For the consummate expert or for those cases where an appropriate film brand/type/speed profile does not exist, Negafix Expert mode allows duplication and customisation of profile mapping.
Negafix result:
Accurate image data from negative film.(Automatic)
Color Cast RemovalThe Color Cast Removal tool removes colour casts caused by light temperature variables. These might include sunrise, sunset, overcast skies, florescent lighting, tungsten lighting, etc.
Removal of the colour cast is optional. As Ian Lyon points out in his excellent SilverFast tutorials (see the section
The Levels Histogram), there are occasions when the colour cast is desirable such as the colour cast caused by a sunset. In these cases, the Color Cast Removal tool would not be used or would only be used to a limited degree (ie, somewhere between 0% and 100%).
Automatic colour cast removal was designed principally as a batch scanning tool. A real-world example of its use: a roll of APS film whose images include:
- photographs shot outdoors on a sunny day (no cast)
- photographs shot outdoors on an overcast day (blue-ish cast)
- photographs shot indoors with florescent lighting ('dirty' green cast)
- photographs shot indoors with flash lighting (no cast)
Automatic colour cast removal allows SilverFast to automatically remove the different colour casts without intervention by the user. Note that these colour casts are not a characteristic of the film itself, and hence should
not be affected in any way by Negafix. Nor should they be affected by calibration.
While the Color Cast Removal tool provides automatic colour cast removal, SilverFast also provides the
Global Color Correction tool which allows the user to manually and very efficiently create, edit or remove any colour cast within the image.
I believe that Color Cast Removal affects the whole dynamic range of the image, not just the end points. Color Cast Removal may not be as absolute in the middle as it is at the end points but it will never the less have a visible effect.
Color Cast Removal remaps the end points of the RGB colour data which is then redistributed to utilise the full dynamic range of the image subject to the (Auto) Threshold values. This redistribution or stretching of the colour data indirectly affects the mid-tones effectively removing much of the colour cast found there. Pressing the Option key while viewing the histogram data will show that the mid-tones are redistributed along with the end points of the image.
Color Cast Removal result:
Accurate colour without the unwanted effects of light temperature variables.
Conclusion
These are my impressions. They may be incorrect. Hopefully, Lasersoft will point out any errors in my logic.
Currently, SilverFast disables calibration when Negafix is used. I (and a few other people in the
Tips & Tricks forum) don't agree with this logic but that's the way it is. Hopefully, combining SF Ai and SF HDR will allow us to use both Calibration and Negafix together.
Back to the original problem:
When SilverFast is
first installed (very important point), automatic Color Cast Removal will be triggered whenever the Image Auto-adjust tool is used
if the Auto: Color Cast Removal value is non-zero, and the CMS:Scanner > Internal value is <NONE>. This is true for both Positive and Negative scan types.
If Scan Type is then set to Positive, CMS: Scanner > Internal is changed to Calibration or ColorSync and a scanner profile is specified via CMS: Scanner Profile, automatic Color Cast Removal will be disabled (the Image Auto-adjust button will be coloured).
At this point, I only perceive a problem in the
logic that automatic Color Cast Removal should be disabled when Calibration or ColorSync is enabled. As I have already stated, I believe that Color Cast Removal should be independent of Calibration or ColorSync.
If Scan Type is now reverted to Negative, SilverFast automatically reverts CMS: Scanner > Internal to <NONE> and
disables the CMS: Scanner Profile effectively turning Calibration or ColorSync off. Now, even though SilverFast has automatically reverted CMS: Scanner > Internal to <NONE>, automatic Color Cast Removal is still disabled (the Image Auto-adjust button is still coloured).
If we now switch Scan Type back to Positive, set CMS: Scanner > Internal to <NONE> and CMS: Scanner Profile to <NONE>, and then switch Scan Type back to Negative again, we can see that automatic Color Cast Removal has been activated once again.
So what's going on? Does the scanner profile still affect the CMS workflow even when its disabled by the switch to Negative Scan Type?
Or is this a bug?
Many thanks to Ian Lyons for his replies. Even though we may have different opinions, his replies stimulate further examination and learning of the SilverFast environment and imaging in general; always a worthy and educational exercise.
P.S. In general, I abhor flashy web technology too, especially HTML email messages and Flash 'enhanced' web sites.
kind regards
Gregory
(time to walk the dogs, take a break and contemplate the meaning of the universe and life itself
)
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