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I'm editing some RAW images using RawTherapee, and after editing I'm seeing a significant amount of noise that wasn't present in the original RAW image. I'm increasing the exposure, contrast, and saturation. I've posted links to the files on my Google Drive.

Original RAW Image https://drive.google.com/file/d/0B1AevSHD2CtcUXVfSGpBS2xqMm8/view?usp=sharing

Edited image (JPEG output) https://drive.google.com/file/d/0B1AevSHD2CtccHNaQ29JR0I2YVU/view?usp=sharing

As you can see in the edited image, there is a ton of noise, especially in the sky.

What exactly is causing this noise to appear, and what can be done about it? Is it the kind of edits I'm making that's causing it or is it just noise that's already there that I'm only seeing when I make these edits? I'm very much a novice (I picked up photography about a month ago), so would you guys recommend just editing in JPEG for now? I don't recall running into this issue on the few JPEGs I've edited.

Thanks in advance!

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The noise is present in the original file.

What you have done with your choice of settings is amplified it. Noise is mostly present in dark areas but you have basically applied gain to those areas and hence to noise noise.

All channels have noise but the blue and red channels have more noise since they are formed using fewer photosites. In your processing, it is clear that you increased its level beyond anything resembling reality. Keep it down. A friend said processing is like applying make-up: A little goes a long way but too much looks trashy.

To reduce this issue, you need to improve the exposure right in-camera which will allows you to get better output since you will not to apply go much gain. The simplest and on of the most effectives is to Exposure-To-The-Right (ETTR) as described in the linked answer on mine.

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  • \$\begingroup\$ Thanks, that makes a lot of sense. I did in fact take two more shots at higher exposure levels. The reason I didn't use those is because 1) The signs on the buildings are blown out and sometimes unreadable. For example, the Transamerica sign blurrier on the brighter exposures, and the FNB and Sun Trust signs are almost unreadable 2) The sky looks washed out, and you don't see the deep red/orange hues of the sunset. With the sky in the light exposure, I should be able to up the saturation and contrast without amplifying the noise, right? What do I do about the blown out signs though? \$\endgroup\$
    – user2654217
    Jun 20, 2017 at 11:11
  • \$\begingroup\$ Oh and here are the lighter exposures for reference. Thanks again! drive.google.com/open?id=0B1AevSHD2CtcS1o1QmtuNC01QWM drive.google.com/open?id=0B1AevSHD2CtcQmpxOEpIMXRfWVU \$\endgroup\$
    – user2654217
    Jun 20, 2017 at 11:15
  • \$\begingroup\$ @user2654217 The middle exposure is probably the better starting point but you do have a scene which exceeded the dynamic range of the camera, so this is when people often use Exposure Fusion. If your shots were taken from a tripod, you can easily give it a try with Enfuse. Unfortunately, if you want the buildings backlit by the sunset, it is simply what the situation will be. \$\endgroup\$
    – Itai
    Jun 20, 2017 at 13:24
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There are several things that can increase perceived noise in a photo:

  • Increasing brightness/exposure in post processing. When you amplify the shadows you also amplify the noise in the shadows.
  • Increasing saturation. The will particularly affect chrominance noise.
  • Applying peripheral illumination lens correction. If you use lens correction to brighten up the corners of a photo that has light falloff in the corners you are raising the brightness levels of the corners. The noise in those darker corners will also be raised.

After editing I'm seeing a significant amount of noise that wasn't present in the original RAW image.

There's really no way to see an "original raw image." Raw data is much like a latent negative. It can wind up looking a lot of different ways depending on how we develop it and how we print from it. Luckily, for digital raw image files we don't have to make irreversible decisions like we do when developing film.

What may be happening when you first select the image you are viewing is that you are seeing the jpeg preview generated by the camera and attached to the raw file. Many raw processing applications use the attached preview jpeg to display thumbnails of raw image files. Depending on your RawTherapee settings, you may be seeing the jpeg preview image when you first open an image file. The jpeg preview image probably had an amount of noise reduction applied by the camera.

Or you may be seeing how the default options in RawTherapee interpret the data from the raw data. In any case, your monitor can not simultaneously display all of the information contained in the raw file. It has to be interpreted to be displayed on a monitor.

If you were importing your raw files into Canon's Digital Photo Professional then the application would be applying the same settings that you had set in-camera at the time the image was taken and the result will look near identical to the camera generated preview image.

When you start editing in RawTherapee many of the in-camera settings applied to the jpeg preview are ignored. RT opens your raw image and applies its default profile instead. If your default profile in RT does not include any noise reduction and you don't add any while editing then none is being applied to the image as you edit and export it. Even if you do apply some noise reduction, if it is less than what the camera applied to the jpeg preview, then your edited image will be noisier than the jpeg preview you saw when you selected the image.

For more, please see:
Why do RAW images look worse than JPEGs in editing programs?
Why do RAW images in Darktable have a lot of noise?
While shooting in RAW, do you have to post-process it to make the picture look good?
Why is there a loss of quality from camera to computer screen
Why do my images look different on my camera than when imported to my laptop?
How can I undo Canon Auto Lighting Optimizer in Lightroom? Although the question is different, this answer directly explains what you are experiencing.

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