Gain - in camera or in post

marks27 wrote on 11/23/2008, 6:41 PM

I recently shot a dance event (3 cameras - Sony Z1's) and had a lot of trouble with the lighting (generally low light, and fluctuated from blackhole to supernova).

Anyway, got me thinking (too late), so i am interested in hearing people's thoughts: in low light situations, is it better to pump the gain in the camera while capturing, or is to raise the gain/gamma/curves during post?

I am very interested on your thoughts?

Thanks,

marks

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Comments

fausseplanete wrote on 11/25/2008, 11:59 PM

Also if levels are left low in the camera then only a few of the (typically) 8 available bits wil get any nonzeroes, so the levels will be more quantized, although then I suppose the noise might actually help by (accidentally) dithering these.

Agreed, S-curves etc. are brilliant e.g. for flattening shadows, hence removing more noise than noticeable detail (on some relative psychological scale of units!).

Underexposing to avoid "video look" I am not so sure about. I used to do that with my Z1, to avoid "video" look e.g. room lights not saturated blobs, then boost using S-curves. But then found I needed some kind of denoising software again, which is CPU-intensive. I wonder if the advisability of this depends on the signal/noise ratio in the camera, in which case maybe only advisable for higher-end cameras or at least better s/n (maybe the EX's ?). Any opinions on this?

tumbleweed2 wrote on 11/26/2008, 8:44 AM

I'm no expert, but in the old analog days, it was common for a broadcast quality cam to have a S/N ratio of 62db or higher, where as todays prosumer & lower end professional units seem to be touting 54db levels, the EX1 for example... & I'm pretty sure your Z1 has a 54db level...

My reasoning for underexposing some was to not lose all the detail in the highlights & still be able to bring up my blacks to show some detail that is there....

Serena wrote on 11/26/2008, 1:55 PM

"My reasoning for underexposing some was to not lose all the detail in the highlights"

Yes, that is fine but not always achievable within the dynamic range of 8 bits. However that isn't the problem explored in this thread. You need to go back to the top and read the question and the first few responses. Would be better to start a new thread if you want to discuss the general question of how to optimise exposure under well lit conditions.

tumbleweed2 wrote on 11/26/2008, 9:45 PM

"However that isn't the problem explored in this thread"

I was only answering the previous post.... I'm on the wrong website if that isn't allowed... : )

Serena wrote on 11/26/2008, 11:05 PM

Well that seems OK then! These threads wander so much that it is often very difficult to locate good stuff that one remembers. Only reading the last post (and responding) tends to confusion, but undoubtedly I've done it myself.

fausseplanete wrote on 11/26/2008, 11:09 PM

@Serena: I started a new thread as you suggested, at [http://www.sonycreativesoftware.com/forums/ShowMessage.asp?MessageID=626429&Replies=5].

Lou van Wijhe wrote on 11/27/2008, 3:13 AM

xfx wrote:
I often shoot some night shots in very low light on a fig rig in the crowd where it’s impossible to bring in big lights
So when I edit that clip I duplicate track and use add as compositing mode, it’s amazing how the clip pumps up. Use the sliders if the highlight washes out.

Thanks a lot for this tip! I filmed a large cave in Vietnam with the gain on the camera switched off to avoid grain. The cave was illuminated with floodlights and the shots looked clean but the shadows were too dark. Using your tip the shots still looked clean but you could even see people walking about in the shadows. No need to correct for washed-out highlights.

Lou

Rory Cooper wrote on 11/27/2008, 6:10 AM

glad i could help

Just as a matter of interest after you ‘ADDED” were the lights in the cave washing out nearby detail

And are you filming prog or interlaced ?

Rory

Lou van Wijhe wrote on 11/27/2008, 10:49 AM

Hi Rory,

The original shots were taken with a Canon HV20 in (progressive and) spotlight mode, whereby gain is switched off and exposure is based on the lightest parts, like on openings where daylight seeped through.

The main effect of the ADD operation was that detail in dark parts became clearer whereas lighter parts didn't look overexposed at all. The overall effect was very pleasing. All in all, the cave's interior looked as if it had been professionally lit and no grain was visible in the shots.

Lou

Rory Cooper wrote on 11/27/2008, 8:53 PM

Thanks Lou

I will try the spotlight mode next time I film in low light "canon hg10''

Rory

fausseplanete wrote on 11/28/2008, 3:22 AM

xfx,

If you're going to use auto exposure, then I think you want the opposite: "backlit" mode (as it's called in some cameras), not "spotlight", to make the auto exposure tend to disregard rather than be dominated by the brightest objects (eg lights).

For example I did that recently when shooting (unfortunate ambiguity) a bird against the dusk sky. I used auto rather than manual exposure simply because the shoot was over a period of time when daylight was diminishing rapidly.

Rory Cooper wrote on 11/28/2008, 4:05 AM

Thanks fausseplanete

I appreciate the advice

Also thanks for not getting too technical
My filming is improving and all these little bits of info really helps

Lou van Wijhe wrote on 11/29/2008, 3:56 AM

Spotlight Mode is for what the word says. If the subject is brightly lit and the surroundings are dark, this mode prevents the subject from getting overexposed. It is not for general low-light situations. It is ideal for use in theaters, night shots of illuminated streets, etc. Even in harsh daylight it can come in handy, think of a sunlit flower against a dark wood backdrop.

Lou