Noise Reduction and RAW

[hernhombeecaryb]

I use a Rebel T4i, but the model really should not matter I think.

When Hi ISO or Long Exposure Noise Reduction is set does it apply to RAW?

I am under the impression that RAW get no additional processing. But I'm learning to look at my images in new ways. Something doesn't add up. It seems like the noise reduction is applied to RAW images. My mind is going to explode pretty soon if somebody doesn't set me straight.

[ebiggs1]

Don't explode!!!!!!  

If you've saved the file in raw mode and it is later loaded into a raw conversion program (PS, LR, DPP) and then saved to a TIFF or .PSD it can be exported in 16 bit mode.

Camera's record either 12 bit, 4,096 brightness levels, or 14 bit,16,384 brightness levels. If you've saved the file in the camera as a JPG, it is converted by the camera to 8 bit and you will only have 256 of brightness levels.

In post this can be spread over the entire16 bit workspace.  No camera at present does 16 bit that I know of.

This raw image data, what the camera sensor saw along with meta-data is now saved to the card. Some cameras compress these files. If they are compressed it is done losslessly so that there is no deterioration of the file.

A raw file is essentially the data that the camera recorded along with some additional information piggy-backed.

A JPG has had the camera apply linear conversion, matrix conversion, white balance, contrast, and saturation, and has destructive compression applied.

A RAW holds exactly what the sensor recorded. Nothing more. Nothing less.

But the biggest advantage with raw is the 16 bit image in post. You have 65,536 levels to work with. Where a JPG 's 8 bit has that measely 256 brightness levels. This is very important when editing a photo.

However this does not mean to say RAW is the answer and JPG should never be used.  They are simply tools the camera has.  You must make the best use of each.

If you are a guy that just posts to Facebook, JPG is just fine.  If you are going to make 4x6 snapshots for grandma at Walmart, JPG is just fine.  If you are in a big hurry and or don't have post handy, JPG is just fine.

 On the other hand if your work is critical or you are making fine prints, RAW is the answer.  And of course you need to have the software and knowledge to use it.

One word of caution, don't listen to the RAW "snobs".  Use each format to your advantage.  Each has it's place in photography.  Is it any clearer or is it still foggy?  

[Skirball · Accepted solution]

Long exposure noise reduction is applied directly to RAW.  It's "destructive", burnt into the file.  It takes the noise readings from the second "dark" shot and subtracts them from the first image, and creates a single RAW out of it.

High ISO noise on the other hand is just listed as a setting.  Programs like Lightroom will ignore it, but some programs, like Canon's DPP will apply it on import.  I don't use it so I can't say for sure, but I'd imagine that you can adjust it since it's just a setting.

[hsbn]

Like Skirball said, but also depend on what software you use to view your RAW file. Some software will display imbedded JPG in the RAW file instead of the RAW itselft. If this is the case, then you'll see noise reduction applied (because it is applied on the embedded JPG). Aslo Canon DPP can view this.

[hernhombeecaryb]

Skirball, can you elaborate a little more on "the second dark shot". I understand how noise removal will use it with a subtraction (XOR function), but I fail to find mention of it related to the T4i documentation. Just point me in the right direction, I can dig up the details myself. Thanks!

[Skirball]

When shooting long exposures certain pixels will heat up more than others creating noise.  The good news is that thermal noise is repeatable, the same pixels will heat up more or less the same amount.  So the camera takes a first picture of whatever you’re shooting, then takes a second picture without opening the iris.  Theoretically the second picture would be pure black, with no data for any pixel.  But the hot pixels show up and those values are subtracted from the values given by those same pixels in the first picture, which should give the true value that it would have been without thermal noise.  Make sense?  All of this is done in camera, and you get one single image from the two shots. 

[ebiggs1]

The second dark shot is exactly the same as the first regular shot except the shutter does not open.

Some folks say you can map out "hot pixels" doing this. (?)

JPEG images are processed into finished files in your camera. Then they are written to the memory card.  All color and detail information is written to your final image.  Settings affecting image quality that you make in the camera are immediately visible in finished JPEG images.

RAW images are more dependent upon how you process the RAW file.  The RAW finished image is made in your computer. Using your favorite RAW file processing software.

Adobe’s Camera Raw, (ACR) and my favorite, ignores in-camera settings including High ISO Noise Reduction or Long Exposure Noise Reduction.  You will have to use Adobe's tools,( ACR, Lightroom, or PS) to change your final photos.

In Digital Photo Professional, you can independently adjust chrominance and luminance noise reduction beyond what the

in-camera settings were.

[Skirball]

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@ebiggs1 wrote:

Adobe’s Camera Raw, (ACR) and my favorite, ignores in-camera settings including...  Long Exposure Noise Reduction.

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That's incorrect.