Crispening effect on noise: which luma range?

[Piotr Wozniacki]

While trying to make the best use of the Crispening setting for my various PPs on the EX1, I realized one dilemma has never been definitely and conclusively addressed on this forum:

- does Crispening setting affect detail across the entire luma range, or just low-light areas?

In the thread http://www.dvinfo.net/forum/sony-xdc...mma-noise.html, some people (e.g. Serena) suggested it only affects the low-luma range; others (e.g. Simon Wyndham) insisted that on cameras without Level depend adjustment, Crispening applies to detail in the entire luma range.. Mind you - that discussion took place before the 350 arrived; also, both parties referred to Sony's information contained in their "creative shooting techniques" webpage at Sony | Micro Site - XDCAM EX.

So - while with the new 350 XDCAM EX camera, which has the Level Depend setting implemented - this question might be considered as answered, in the case of the EX1/3 it's still open.

To complicate things even more, our forum's guru Alister recommends positive Crispening setting, while the BBC's Alan states negative setting should be used.

And finally, without using truly professional equipment/methodology, it's very difficult to assess this particular setting influence judging with just a naked eye...

Personally, I always used higher Crispening values in low-light situations, where large areas of single-color, dark objects (walls and alike) inevitably suffer from excessive noise. With plenty of light, I dialed it down to negative values, hoping I could take full advantage of the available sharpness without amplifying noise... But now, I'm really not sure this has been the right thing to do, again!

Welcome to a discussion - but please, those using both the EX1/3 AND the 350, do differentiate which of those two camera classes you're talking about.

[Alister Chapman]

Crispening works across the entire luma range. It's really difficult to explain how the level adjustment works, it is a threshold adjustment for the detail circuit, but I'll have a go anyway.

First off lets consider how the detail circuit works. The camera uses delay circuits to compare how the brightness (luma) levels of adjacent pixels are changing, both from left to right and line by line. If the circuit sees a rapid change from light to dark or dark to light (or light to lighter, dark to darker etc) the circuit regards this as an edge and detail correction is applied by brightening or darkening the transition, exaggerating the edge. This is seen in extreme cases as a black or white halo around edges.

On the EX cameras crispening works by adjusting the threshold at which the light to dark transition between pixels triggers the application of detail correction. So when you set a negative number, say -99 even the slightest luma difference between pixels will have detail correction applied. Set it to +99 and it takes a much greater luma change to trigger the detail circuit.

What you need to understand is that if you set crispening such that the threshold before detail is applied is 100mV (for example) then between 0v (black) and 99mV little to no detail correction will be applied, keeping blacks clean by not applying detail correction to any noise with an amplitude less than 100mV. But if there are subtle textures in the image, going say from 500mV to 599mV (mid tones) then no detail correction will be applied here either, so the image will appear a little softer, only larger luma changes of more than 100mV will have detail correction applied. These small luma changes can be anywhere within the full luma range and it is not confined just to the darker parts of the image.

Raising the crispening level setting to a positive number raises the threshold at which detail is applied to the image, so a high number prevents detail correction from being added to small luma changes. A negative number means that detail correction will be applied to smaller luma changes, this increases the appearance of noise but also makes textures appear sharper.

I don't really know why Alan Roberts went for a negative value, it seems counter to what he is normally trying to achieve which is a clean image that mimics film. I like to run crispening at +10 or higher just to help with image noise.

Sony have a PDF about it here:
http://www.sony.co.uk/res/attachment...6605183226.pdf

Why Alan Roberts specified a minus value I don't know as this clearly increase value

[Piotr Wozniacki]

Thanks Alister - while understanding your reasoning, I still believe one can "afford" negative crispening values with full of light (when the noise is minimal), and only set it to positive values in low-light conditions (at least this is how I set my PPs). Watching those super-sharp HD productions on the Polish HDTV broadcast, I can see they are terribly noisy when shot in dark insides, but as clean and sharp as a razor in full sunlight (or studio lighting).

Also, in the excerpt below, I guess you meant "raising the crispening level...", and not " Raising the detail level setting..." - am I right?

Originally Posted by Alister Chapman

Raising the detail level setting to a positive number raises the threshold at which detail is applied to the image, so a high number prevents detail correction from being added to small luma changes. A negative number means that detail correction will be applied to smaller luma changes, this increases the appearance of noise but also makes textures appear sharper.

[Piotr Wozniacki]

Have no idea why my post appeared here...

It should go after your last post!

[Alister Chapman]

Yes, it should be raising the crispening level.

One thing to consider is that the noise the camera produces is not only in the blacks. If the noise amplitude (level) is for example 5mV, then if you have a subject at 500mV (mid tones) it will still have random 5mV noise added to it. It just tends to be that noise is most visible in the blacks as 5mV of noise on a 5mV (very dark) signal is modulating (varying) the signal by 100% so it's quite obvious, however 5mV on top of 500mV is only 1% so less obvious, but still there and still visible.

One thing to take into account is that the cleaner you can make the recorded image the less stress there is on the codec. This in turn means less mosquito noise and macro blocking giving an image that looks cleaner still and grades better. I struggle to see the difference between crispening at 0 and at +20 in most normally exposed shots, but if I look closely I do see less noise in shadow and low contrast areas. Low contrast areas tend to have little detail anyway, so being able to clean these up a little helps in post production.

[Piotr Wozniacki]

Agree 100% - thanks a lot.

Piotr

[Leonard Levy]

Alister,
Yes! - Thanks Alister - that is the only good explanation of crispening I have heard in my life. Very clear. I will have to think a bit to figure out how this affects my images in practice, but after 25 years you have finally cleared up a complete mystery. How about how it interfaces with frequency next and then Horizontal vs. Vertical Detail. Detail has always been a dark hole for me.

Lenny Levy

[Marty Welk]

thanks Alister Chapman , now if you could just put into HUMAN language all the rest of this stuff :-)

Ex1r
i noticed wierd areas of noise on particular things in my test setup, like a brighter lime green of all things, and the crispener adjustement got rid of that noise, The noise i saw should not (nessisarily) have been caused by edge sharpeneing stuff.
Great point about making a clean image before it gets compressed with the codec.

Another thing i have been wondering is WHY these cameras are using so much "false sharpeneing" with a HD signal that is going to be compressed so highly. I was looking at the 350 pics posted, and it was doing that too.

It seems if you got that many pixels per inch the point of sharpening excessivly seems to be lost, causing more unnatural looking stuff especially on certian details. Then playback is going to be Pixel-for-Pixel on Digital displays UNLIKE the smoothing that goes on with analog stuff.
Examples Sort of like sharpeneing our high-res Computer LCD monitors, something that wouldnt help seeing fine detail, and only help distance viewing when that kind of detail can even be seen AT a distance.

I shut off a lot of that stuff completely, and view the more rawer signal and on the HD tv in HD it still looked great. getting up "too Close" to the BIG tv the excess sharpening just looks wrong.
When it comes to downscaling to SD signals all that excessive sharpening seems like it is just going to cause ummm whats the word flickering, moiereing and interline noise stuff?