Does anyone have any insight on detail coring frequencies? I've been experimenting with the detail settings on my 27V and have yet to divine the scientific explanation behind coring. Anyone able to enlighten me on this? Many thanks...
Greg Gillam Producer/Director
Red Sands Production Co. Denver
You might check out this site. It's full of interesting, well presented information.
Warmest regards to all,
John R. Schilberg VP
Sales & Engineering Broadcast Digital Systems
Coring and detail frequency are two different things.
Detail frequency is the horizontal frequency at which the maximum peaking takes place. To visualize this, imagine shooting a multiburst chart with a camera that has a hypothetically flat frequency response. As you turned the detail level up and down, you'd notice that one frequency was affected more than the others and that the response fell off in a gaussian fashion on either side of that frequency. That is the horizontal peaking or corner frequency. From a practical standpoint, detail frequency affects the width or edge of the horizontal detail enhancement. It can also be used to create a flat(er) frequency response when using a real-world camera and shooting a multiburst chart.
Coring is used to remove fine detail information that does not contribute significantly to the detail of the picture but which adds noise to the image. Imagine the detail information viewed on a scope. About the baseline you'd see primarily the noise information, with the detail extending beyond that. Now imagine that you sliced (or cored) this signal so that only the information above the noise on the baseline came through. You would be left with most of the detail information intact but with much of the noise information removed. The coring adjustment determines how far from the baseline the detail information removed. You want to use just enough coring to reduce the noise in the picture but not so much that the fine detail in the image is affected.
I hope this helps.
Detail coring is a technique that allows the goodness of image enhancement - the crispening of video image edges - without driving up noise in the image.
Most of the need for enhancement lies in the brighter regions of the image. The human visual system has less acuity/need for edges in the darker areas.
Coring takes advantage of this by setting a brightness threshold - usually around Zone 3 (Ansel Adams perspective) below which the enhancers are turned off.
Two good things happen. Blacks and shadows are cleaner because they are not enhanced. Further, gamma circuits increase gain (noise) in the darker areas and decrease the gain (and noise) in the bright areas. By not enhancing the darks regions we avoid enhancing the added noise introduced by gamma in the shadows.
To set this coring adjustment you will need a waveform monitor:
Look at the chip chart with enhancement turned on.
On the WFM you will see the characteristic enhancement "spikes" along the stairsteps in the waveform at the edges of each chip.
Temporarily increase the enhancement gain to help see the spikes if necessary
The spikes should suddenly stop on the lower 2-3 steps.
The coring sets the desired brightness step/threshold where enhancement begins.
If you work the coring adjustment you will see the enhancement edges turning on and off step by step up and down the chips stairsteps waveform.
Once you have the coring threshold set to enhance things above step 2 (suggested serving) return the enhancement setting to its preferred/nominal value.
+ + + + + There is also a noise gate circuit - another form of coring - that operates on enhancement all across the range of brightness. This adjustment sets the minimum amplitude difference between compared video elements on either the H or V axis that will be enhanced.
It is another point of noise suppression in the enhancement system.
All we want to enhance is the image - not the random noise. Disclaimer: not all cameras are designed or created equal. My descriptions above are generic and intended as a guide only. See camera manuals for *full details* on adjusting your type of camera. (Full details - get it - enhancem- uhh - never mind... )
Hope this info is useful.
Pete Fasciano Co-founder Fellow,
Advance Development Avid Technology
The definition for coring/crispening/level dependency/threshold are sometimes interchanged, even by some camera manufacturers. Generally though, what you described is usually referred to as Level Dependency or Threshold - detail correction that is gated on and off by the level of the video signal itself. This affects the entire detail signal. Coring or Crispening is the process of removing low level detail information (think of it as removing the core of an apple and leaving the important parts of the apple intact) irrespective of the level of the video signal itself. This affects only the low amplitude portions of the video signal.
Tom wrote :
>By and large I think you may well be correct.
The fact that there is no standard terminology among cameras can add to the confusion. I just want to resolve a bit of confusion in your last sentence below.
Agreed on your description of coring. I referenced it in the bottom of what I wrote. What is unclear in your last line is the terminology - it sounds closer to the threshold setting process.
How does this tweak to your language hit you? "This affects only the low amplitude portions of the *enhancement* signal."
Coring as you indicate does indeed affect (remove) the low level *differences* between compared lines and picture elements in the enhancement circuit - but at all levels of brightness above the threshold setting.
I think we are both working to get our concepts framed correctly.
Another thought for benefit of all. The noise levels obviously rise from 0db +9db +18db to +24db of boost. At about +6db per stop a +24db boost is a 4 stop push. Comparatively noisy.
Your thoughts on setting coring limits at various degrees of boost?
Many cameras (Ikegami immediately comes to mind) automatically increase the setting for coring/crispening at higher camera gain setting (or offer mutliple settings tied to gain) for just this reason. I normally run low detail levels and 0 or -3 gain so I typically use no level dependancy and minimal crispening.
Thanks to everyone for explanations on Coring. If it were called "threshold" in the menu I would have understood.
Red Sands Production Co. Denver, CO
Not to further confuse the issue, but many cameras, e.g. the Thomson LDK series (Philips, BTS, Etc.) cameras provide Noise Slice (analagous to Crispening) and Level Dependence (analagous to Threshold). In the Thomson LDK Digital SD and HD cameras; Noise Slice and Level Dependence are really just tools that allow for the optimum use of Contour (Detail) enhancement while limiting the noise normally associated with Contour and Black processing circuitry. Noise Slice normally functions primarily at the video Gamma crossover point (45-55 IRE) and Level Dependence normally functions primarily near or just above Black. Even if you run nominal (50-60 on a scale of 0-99) Contour (Detail) Level, very minimal Contour noise reduction (Level Dependence and Noise Slice) is required (4-5 on a scale of 0-99)in these cameras because of the inherent "quietness" of the Digital Contour and Black processing.
In my experience, however, many first time HD users, normally accustomed to film, are actually put off by the low noise levels, however, as they are used to seeing more grain, vaguely analagous to the noise in video cameras. --
George C. Palmer HDPIX, Inc.
An Imaging Services Company
You know, it is even worse for people of non English spoken countries. Sometimes it is very hard to find the proper word to translate technical terms.
Jesús HAro (Spain based )