How to Shoot Virtually Noise Free RAWs :) - RAW Shooting and Processing - CHDK Forum
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How to Shoot Virtually Noise Free RAWs :)

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Offline Mr_Speedy

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How to Shoot Virtually Noise Free RAWs :)
« on: 22 / December / 2011, 18:04:09 »
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I thought I'd post a few tips that will help people get the cleanest possible RAW files, and post-processing (noise reduction) that will help even more. Add your own findings and opinions!  :)

I have found what some other people found, which is that sometimes even low ISO (ISO 100, ISO 80) files are overly noisy, here are some tips for an entire workflow:

1) Shoot at the lowest possible ISO setting. I have found that overriding the ISO to ISO 50 works often (it works on my Powershot A640 and Powershot SX130 IS). However, the lowest native ISO is just fine too.
-If you choose ISO 50, remember to compensate your exposure accordingly. I find it easiest to use the camera's ISO 100 setting and set the exposure dial to +1 (then use CHDK to override to ISO 50).

2) Experiment with overexposing the image (Google "expose to the right").
Simply put, you overexpose the image a certain amount (I overexpose by one stop), which will result in a cleaner RAW file. The value you can overexpose by without blowing out the highlights varies from camera to camera... I dont think you will get very different results from me (using a point and shoot camera, dSLR cameras are more flexible). If you are shooting a scene where you are already in danger of blowing out the highlights, then do not overexpose the image.

3) When you open the RAW (DNG) file on your computer, reduce the exposure setting in Camera Raw or other program, by the amount that you overexposed by. Or simply darken the image with the exposure setting until the exposure is correct and there are no highlights being blown.

4) Noise reduction. I use Noise Ninja to reduce noise, but there are other programs out there.
To get even better performance from Noise Ninja than the standard settings, make a camera profile for each ISO setting on your camera. This involves photographing a chart at each ISO setting, and putting the images through the program. Use the profile for the ISO setting you shot with when you reduce noise from that image. You can read more about that in the manual for Noise Ninja.

5) Optional: Depending on your needs, if you do not need full resolution, resize your image to a smaller size. I find viewing at 100% shows a certain amount of noise. Resizing to 50% gives a perfect picture if using a low ISO. Resizing to 25% gives good results with the high ISO files.

That's it!  :)

I'll post a couple images so you can judge for yourself  :)

Here are 3 DNG images straight out of the camera, as well as 3 PNG images made from those DNG after I have applied my workflow (correct exposure, noise reduction and sharpening). EDIT: I needed to do more sharpening.... I'm still perfecting my workslow.
http://www7.zippyshare.com/v/14641985/file.html (80MB) 3 random pics I took indoors to test my workflow.
« Last Edit: 23 / December / 2011, 04:40:36 by Mr_Speedy »
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Offline dynamix

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Re: How to Shoot Virtually Noise Free RAWs :)
« Reply #1 on: 07 / January / 2012, 10:45:02 »
nice tips, will definately use it.  :)
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Offline Lebeau

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Re: How to Shoot Virtually Noise Free RAWs :)
« Reply #2 on: 07 / January / 2012, 11:58:04 »
Point 5: Demosaicing process creates virtually colored pixels from adjacent Bayer pixels. When you are rescaling to 50%, you are doing equivalent to un-demosaicing, returning to "real" pixel resolution.

Demosaicing and un-demosaicing processes generate less quality than Canon sRAW format where a Bayer quartet becomes a raw pixel. No virtual pixelisation to de-virtualize, just RGGB Bayer quartet forms a RGB raw pixel. "sRAW" stands for small raw, at 50% of the demosaiced captured raw.
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Offline Mr_Speedy

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Re: How to Shoot Virtually Noise Free RAWs :)
« Reply #3 on: 11 / January / 2012, 03:07:29 »
Well, I am sort of regretting not buying the older Canon Powershot SX120IS (I bought the newer SX130IS).

You more or less need bright daylight to be at full zoom and still use ISO 80. That's what you get for buying a point and shoot with a slow lens  :(

Anyway, that is one thing I did not mention in the original post, obviously ISO performance concerning noise depends on the camera sensor, but it also depends on the camera lens. A camera with a faster lens is going to let you use low ISO more often than slow lenses.
If you're zoomed in, the aperture gets smaller (higher F value) and you get less light to the sensor. This means you will be forced to crank up the ISO = more noise. (not to mention that you will need a faster shutter speed to get a sharp image, further raising the need to boost ISO levels). If you can, get closer to the subject or back off a little with the zoom, you may be able to lower the ISO by one or more stops.

Here is another example of an ISO 80 DNG and PNG:
http://www52.zippyshare.com/v/83399407/file.html
« Last Edit: 11 / January / 2012, 03:10:33 by Mr_Speedy »
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Offline Pier

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Re: How to Shoot Virtually Noise Free RAWs :)
« Reply #4 on: 11 / January / 2012, 04:35:02 »
What You think is loss in % between extra fine lens and these persist in SX130 IS.I don't know.
For such a sensor size is not substantiated, and not possible to use large in diameter lens for more light,
if this percentage is not high enoug.
I know it persist, but is not very high.If existing lens would be replacet, it will be not enough to compesate
the need of more light like the lens to say with largest diameter.
Otherwise the diameter is related to sensor size.
Exept if the lens are very bad quality plexiglass chainamade.Maybe I'm wrong, but have had several expensive old 35 mm cameras with very good lens and they also needs (remember) from more light for quality pictures..
Light is Light ... :)
« Last Edit: 11 / January / 2012, 04:37:59 by Pier »
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Offline Mr_Speedy

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Re: How to Shoot Virtually Noise Free RAWs :)
« Reply #5 on: 11 / January / 2012, 07:00:58 »
At maximum zoom (336mm compared to 35mm film cameras), the SX130IS has an aperture of 5.6. 
At maximum zoom,(360mm compared to 35mm film cameras), the SX120IS has an aperture of 4.3.
This is nearly 1 full stop faster (twice as much light) than the SX130IS.
In simple terms, you can use half the ISO value with the faster lens of the SX120IS.

So in percentages, nearly 100% more light just by going between two point and shoot cameras.

However, there are much better lenses for dSLR cameras. For example, the 300mm 2.8L is an excellent lens. It gives you 4 times more light than the SX130IS and twice as much light as the SX120IS when using it on a full frame camera. (using it on a crop camera will give the same light, but longer equivalent focal length).

Or using the 200mm F2.0L lens with a 1.6x crop camera (like the 1100D) will give you 320mm at F2.0.
This is 8 times more light than the SX130IS (800%)   :)

I mentioned these lens/camera combinations because I was trying to keep the comparison with similar equivalent focal lengths. (around 300mm).


In short...  I would have to use ISO 800 to get a sharp image with my SX130IS, and somebody with the Canon 1100D and 2.0L lens standing next to me could use ISO 100 and still get the same shutter speed because my aperture is 5.6, and his is 2.0...  letting in 8x more light.

He will get nice and clean RAW/JPG images, my ones will be full of noise  :)


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Offline Pier

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Re: How to Shoot Virtually Noise Free RAWs :)
« Reply #6 on: 11 / January / 2012, 11:23:05 »
@Mr_Speedy,
O'Kay about all You said if we play with Fx.
But I'v thought that the word is for the material (glass) of the lenses and they enlighten.I'v know that any expensive binoculars (field-glasses) Svarovski have till 70 layers over the glass, to to let-pass more light.Same  situation and with lens glasses - the type of glass...less or more enlighten...e.t.c.
Thanks.
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Offline Mr_Speedy

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Re: How to Shoot Virtually Noise Free RAWs :)
« Reply #7 on: 12 / January / 2012, 04:56:31 »
I really have no idea about how the type of glass affects the image. I haven't done any research into it.
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Offline PS

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Re: How to Shoot Virtually Noise Free RAWs :)
« Reply #8 on: 17 / January / 2012, 15:02:35 »
Quote from: Mr_Speedy on 22 / December / 2011, 18:04:09
1) Shoot at the lowest possible ISO setting.
If your priority is max. S/N, then shoot at the highest possible ISO and in general max. the exposure.

What is "overexpose without blowing highlights"? (2, 3) Either you overexpose i.e. clip or not.

By permanently downsizing the image you only lose resolution without gaining anything (5).
« Last Edit: 19 / January / 2012, 14:09:53 by PS »
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Offline Mr_Speedy

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Re: How to Shoot Virtually Noise Free RAWs :)
« Reply #9 on: 19 / January / 2012, 10:13:43 »
Overexposing is not the same as clipping. (overexposing leads to clipping if you go too far).
If you are shooting a scene that is fairy consistent in lighting, you can usually dial in either 1/3, 2/3, or +1 stop of exposure compensation (therefore overexposing the image), without clipping any part of the image to white. Clipping starts to occur at about +1 stop and over on point and shoot cameras.

Also, there will be situations when parts of the jpeg image have clipped to white, but the RAW image still contains color information in those areas.

All three images that I supplied in the first post were overexposed to +1, but there was hardly any clipping.

As far as point 5 is concerned, all I wanted to point out was that if the image is too noisy when viewing at 100% zoom, then try viewing at a smaller size. With a 12 megapixel image, you will probably not be viewing at 100% anyway (image larger than screen). Keep the original image, but make a smaller copy that looks best visually to you.

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