XL-1 black level

[Don Bazley]

I've been pretty happy with my XL-1. The one "complaint" I have is that the black levels seem to be crushed quite a bit. I've seen on related threads that the XL-1s can set set-up level. Is there any way to adjust black levels on the XL-1. If not...is there any other recommendations for reducing the contrast?

I'm considering shipping it to Canon for inspection (which I know some folks will suggest anyway). I'd love it if the black levels could be boosted a bit.

-Don

[Ken Tanaka]

Don,

Would a -3dB gain setting help you? I know that many of us use that as our standard setting since the XL1/1s factory settings tend to be a touch hot.

Canon being a Japanese company uses the super black standard. In the USA we use 7.5 ire black (for whatever reason, I tthink super black looks richer).

[Chris Hurd]

The XL1 black level is 0 IRE, however the XL1S allows you to adjust the set-up level in the camera menu. Hope this helps,

[Don Bazley]

Thanks Ken I will try the -3db gain. That is sure to help a bit.

I guess I'm wondering if theres a way that the Canon folks in NJ can boost the black level a bit.

BTW: The suggestion of -3db makes me think of the "spotlight" mode. Does anyone use this? I usually stay in full manual.

(I'm pshched that I just landed a job teaching video production at a college that has....XL-s and GL-1s! This camera has been my hobby to this point. I'm sure I'm going to be getting to know the XL-1 much more this year)

[Ken Tanaka]

That's great news, Don! Congratulations. Of course you'll send your students over here for extra-credit work. ;-)

[Chris Hurd]

Actually Don, Ken isn't kidding at all, your students will be more than welcome here. We can set up a special forum just for them with you as a moderator, or a special account to give them access to all the boards here. Hope this helps,

[Charles Papert]

Ken:

Please help me understand this. I thought that the gain setting is similar to the ASA setting, that it is adjusting the sensitivity of the chips. Thus a mid-level (i.e. plenty of light) exposure of the same scene under different gain settings should have similar gray scale values, the main difference being that the lower gain setting will require the aperture to compensate.

Now how does that effect the baseline black level? Shouldn't that remain constant at 0 db regardless of the gain setting? I have seen that at high gain settings the image appears more contrasty, but I think of that as being a function of increased gamma, wherein the blacks and whites remain constant (0 and 100 ire) but the intermediate points are more steeply stepped.

[Ken Tanaka]

Charles,
Fundamentally the only action that will change the camera's true black level would be...well...changing the black level setting.

(I'm no true video engineering tech but here's my best shot at an explanation.)

I believe that the XL1/1s' AE control would be the closest analog to film's ASA/ISO adjustments, although the analog is somewhat loose. That is, by making AE adjustments you're essentially adjusting the relationship between shutter speed and iris, much as the setting on a film camera performs this function. In a rather metaphorical sense, therefore, you can think of the AE adjustment as an intervention -in front- of the CCD.

I don't think that the gain control has a direct analog in the film world. Rather, it's closest analog may be in the radio world since its setting adjusts the strength of the signal coming from the CCD block. Higher settings=higher signal strength but more noise. Lower settings=lower signal with less noise. Gain settings, however, will not have an effect on the camera's shutter/iris behavior. That is, by the same metaphor above, the gain intervenes -behind- the CCD block.

I've seen people use both AE and gain to very effectively tweak their image to taste. Since the XL1/1s tends to shoot a bit hot, with somewhat noisy blacks, many folks just leave their gain set to -3dB as standard. Ozzie Alfonso's friend who shot those two Las Vegas shows ( http://www.dvinfo.net/conf/showthread.php?s=&threadid=2273 ) reportedly used a Sony DSR-PD150 with his gain set to -5 (!) for most of the shots. And the results were remarkable, although it's a different camera and DSP.

So, while gain does not change the camera's true black setting, by reducing the signal noise it can produce an -apparent- deepening of black levels and, by visual relationship, slightly higher contrast. When you get a chance, it's fun to set-up some test shots for these various settings.

Hopefully someone with more knowledge than I will correct and/or modify my explanation.

[John Klein]

0 dB is the minimum gain on a PD150

Noise will begin to appear with added gain, which may appear to raise the black level but it's just noise.

Not that my NLE is a true waveform monitor, but on an xl1S and a pd-150 it indicates about 5 IRE with no setup added. Everybody says it's really zero in the digidomain, but noise or whatever, it shows to be that.

Both appear to be just a tad under 7.5 IRE with the PD using the 7.5 setup level and the xl1S at +1 setup. I think it's around 9 IRE at +2.

[Don Bazley]

I just wanted to thank everyone for the input on this thread. As time allows I do plan on spending more time on this board. Chris & Ken..when fall comes around I do plan on having my vid prod students use the board. Thanks for the "invite".

Regarding my original post to this thread: It seems that is all I can really try to bring the black level up a bit (or at least appear that way) is try shooting in -3 db. I am going to try this asap. It seems there's no way for the facory to set the black level on the XL-1 (?). Thanks again for all responses.


-Don B.

[Bill Ravens]

The gain setting is, indeed, just like the ISO/ASA rating for film speed. Changing the AE setting is equivalent to changing the ASA dial on a still camera, but, leave the same ASA film in it. The AE setting just biases the light meter plus or minus, while the gain actually changes the sensitivity of the CCD to light. Neither have a direct effect on black level, except for the noise generated as explained by Ken.

The DV standard requires 0 IRE for black. That is a given. Adjustment to black level for NTSC standard has gotta be done in post.The "Black Level Adjust" on the XL1s is more than just pedestal.

[Charles Papert]

Bill:

Please expound on the statement "The Black Level Adjust on the XL1s is more than just pedestal". What else does it affect/what exactly is it doing?

Don:

I had thought that the reported effects here of going to -3db were to improve the noise characteristics rather than raise/lower the black level.

One thing that comes to mind for your dilemma is the use of filtration such as Tiffen's Low Contrast filter, which will elevate the black level. There is a slight softening or blooming of highlights with this filter, which can actually be a desirable effect. I'm a fan of their Ultra Contrast filter which transfers some of the highlights into the shadows, effectively increasing the dynamic range of the camera by as much as a stop, and they don't have the blooming characteristic of the Low Cons, but they have to be used with care. Check out tiffen.com, they have some pictures that demonstrate those filters in use.

[Bill Ravens]

I will tell you what I know, which admittedly isn't much. I don't know the exact details of the "Level Adjust" on the XL1s except that it isn't true pedestal. At nominal, according to my Vectorscope, the IRE is 0. At negative settings, the black level remains at 0 IRE. At +2, the black level is about 7.5 IRE, at +3 it's 16 IRE. At intermediate settings, the black level remains at 0 IRE. The Level adjust seems to also adjust the contrast of the image so that, in addition to pedestal, it's adjusting the "bandwidth" of the entire signal range. All this is the result of testing I did with my XL1s and a vectorscope, so, take it for what it's worth. In order to view images, I had to download into my NLE, so, there's some effect of the image decoding by the NLE codec before I can view it.

As I said, the DV standard is for black to default to 0 IRE. If the XL1s allows you to vary from DV standard, what happens when you try to lay the signal down to tape? The camera's codec, which I assume is according to DV standard, will crush or stretch the measured black signal to 0 IRE. Why, then, did Canon provide this adjustment. If anyone can shed uhhhhhh, light, on this question, forgive the pun, I'd be interested.

[Michael Rosenberger]

Here is some other ramblings that might help:

- DV range for IRE is 0 to 115(120 for some cameras) That is the equivallent to RGB 16,16,16 and around 255,255,255

- Broadcast standard NTSC IRE is 7.5 to 100. That is equivallent to RGB 36,36,36 and 235,235,235.

- Super Black is actually below 0 IRE and is equivallent to RGB 0,0,0. That is what many title programs use for keying.

- As Bill said, the black level adjustments like a contrast control. It will raise your black levels of the video. A good adjustment for bringing detail out of shadows. What it does not do is raise the pedestal (or blanking) of the signal which will remain at 0 IRE. That can create problems. Though your black levels are within broadcast spec above 7.5 IRE broadcast also has the blanking level at 7.5. Your best bet with DV is to shoot your 0 to 100+ IRE and color correct in post, raising the black levels and pedestal all at once. I find once I bring the video signal into spec it smooths out the picture and actually adds to the color saturation.

So back to the original question about lightening darks, you might also consider a simple proc amp.

(As a side note about color correction and broadcast spec. We have had TONS of discussions about IRE and NTSC standards, and I know we all are learning and trying to do things right. The funny part is I just received several PSA's from the foerest service, local wildlife agencies, state parks, and others for this season of show. All were produced by highend production and post houses. Guess what? More than 75% had illegal IRE levels, going down to 0 and well above 100.) The biggest culprit was graphics. Thought you all might get a chuckle.