Fixing Digital Sensor Noise

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Avatar of Shawn Swanson
Shawn Swanson on May 8, 2012 at 3:51 am

Not sure if this is in the correct forum or not, but I think it is. Anyways, My issue is this, When shooting video on my DSLR (Pentax KR) I seem to be getting a fairly large amount of film grain coming in from the footage (lots of green and purple in the darker areas and just general grainy noise everywhere else). I’ve been able to somewhat correct the issue by applying a heavy color corrections to the shots ( high contrast blues, etc. ) which would be fine for action shots, but for shots where I want a “Normal” coloration of the screen I can’t seem to get rid of the grain/noise, Any suggestions? Many Thanks in advance!

Avatar of Jesse Burns
Jesse Burns on May 8, 2012 at 3:57 am

Hey Shawn,

Do you use a custom white balance for each different lighting situation? It sounds like the purple and green shadows could be due to an incorrect white point. Remember to base the white balance on a point exactly where your subject will be, that way the lighting conditions will be the same.

Also if you’re shooting in low-light situations that could be causing your grain issues. What ISOs/shutter speeds/apertures are you shooting at? A lot of grain is usually a culprit of high ISO levels (anything above about 800).

Avatar of Shawn Swanson
Shawn Swanson on May 8, 2012 at 4:12 am

I Had a seeking suspicion that ISOs might have been a culprit, unfortunately the KR has no manual control over anything but White balance and aperture. ISO and shutter speeds are all auto controlled. I’ve been shooting at f/3.5 (Widest I can get the lens). I will definitely try to get some extra lights in and see if it helps at all (I assume since it’s auto ISO if it’s brighter it will bring it down).

Also since it’s videos hard locked at 24fps, if I go into photo mode and wait for the auto shutter speed to read that it can take a photo at 24fps or faster at say ISO 200-400, do you think that be a good read as to whether or not the video would record at around those settings?

Avatar of O'Ryan McEntire
O'Ryan McEntire on May 8, 2012 at 4:17 am

Hey Shawn,
Yea digital cameras tend to produce a lot of digital noise. That’s the term your looking for here. Google search for that will turn up all sorts of advice.

Typically you want to try and avoid it while your capturing your footage. The Pentax KR has an APS-C sensor which is a little on the small side. Which just means that it’s not as light sensitive as a full frame camera. This usually means you have to crank up your ISO to pretty high levels. Think of the ISO as a gain control When you add more gain your driving the sensor harder and you get more noise. Usually you notice it in the shadows first. Those little flickering blue, red, and green pixels.

To avoid this during capture you want to maximize as much light in the scene as you can (with out ruining your mood of course) and keeping your ISO as low as possible.

If you have to fix this in post it can be quite a pain, but still very doable.
There are tools out there that can help out with this one off the top of my head which has great reviews is http://www.neatimage.com/

Typically digital noise is multi-colored and has weird patterns that are distracting tot he viewer. Film grain however tends to be monochrome and has a very organic look to it. often time having a little film grain can add perceived sharpness and cinematic vibe to your digital footage.

Hope that helps!

Avatar of Jesse Burns
Jesse Burns on May 8, 2012 at 4:17 am

Ah bummer man! Those are some very important things to have control over. If you light the scene well then the camera should definitely pull down the ISO and/or make the shutter speed faster (although shutter speed in and of itself does not produce graininess, but simply affects how much motion blur there is).

I never realized how important having artificial lighting was (especially indoors) until I started using it. Not only does it help with the image quality, but it really adds to the mood and allows more control over the “surrealness”, if you will, of the picture. Any movie you watch has a much more surreal look to it, and it is due in HUGE part to carefully placed lighting.

I recommend starting out just using cheap clamp lights you’d find at a hardware store. That’s what I’ve got! I also use different wattage bulbs to be able to change the intensity of the light. It’s amazing how even a cheap light can really improve the picture quality.

Avatar of Jesse Burns
Jesse Burns on May 8, 2012 at 4:21 am

O’Ryan,

Neat Image looks like only a photo processor. Is it able to process video as well?

Avatar of O'Ryan McEntire
O'Ryan McEntire on May 8, 2012 at 4:53 am

Oh shoot, you’re right. They split off into two different apps.
http://www.neatvideo.com/

Avatar of Shawn Swanson
Shawn Swanson on May 8, 2012 at 10:34 pm

Huge thanks to both of you! I’ll check out the NeatVideo demo, and if I can get to a store this weekend I’ll check out the clamp lights as well. Big thanks again!

Avatar of O'Ryan McEntire
O'Ryan McEntire on May 9, 2012 at 5:18 am

Bringing down the blacks can definitely help, but I would advise caution when doing this.

“Crushing the blacks” is often times overdone and can be a sure sign of an amateur or inexperienced filmmaker.

When you crush the blacks too far you loose important data in the shadows. It essentially turns into an inky mess. Now if your going for the Sin City look then this might work in your favor. But typically you want to avoid crushing the blacks too low.

Watch a professional film and you will almost always notice you will never see true black in the image. If you do it’s often a color correction or grading mistake.

The only thing that is truly ever black is the letter boxing on the top and bottom of the image.

Many of the shorts on youtube have this inky crushed blacks look (or the green matrix look) and has kind of become a trademark of stereotypical youtube videos in the professional world.

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