When I've shot night photography in Raw, I sometimes get grainy pictures. Why?
When I've shot night photography in Raw, I sometimes get grainy pictures. Why?
A bit fuzzy question, as you do not show any such image, nor do you analyse what difference there might be compared to images that you consider less grainy or not grainy. So you can only have a general answer.
Grain is something we had when shooting on film, where the image was built up of silver grains. When such grains clumped together in some particular patterns, we saw the image as grainy.
Grain-like structures in digital photography is noise that primarily comes from the sensor, and the noise level is higher compared to the image impressions, when the image impressions are faint, when there is very little exposure.
So you get visible levels of noise when you have dark areas in the image that are not pitch black. The noise is more conspicuous when these dark areas are lifted in development (conversion), to become brighter. Hence if using high ISO, or if lifting dark areas of the image by manipulating the curves, noise can become more visible and provide an image that looks grainy.
The only way to decrease graininess outside noise reduction with software is to increase exposure. Hence lower ISO and more exposure will provide images with less noise, which appear less grainy. Also, holding those dark noisy areas back, so that they do not become too bright in the final image will diminish the appearance of noise. A pitch black area will not seem grainy, while a middle tone area, made brighter in the software, will also have the noise lifted to visible levels.
And the noise is not in any way related to the fact that you shoot RAW, except if the firmware of your camera has noise reduction that is applied automatically. The same noise reduction can also be applied in the RAW converter or later in the process, but often image quality suffers from noise reduction. The image might look better with the noise than without it.
Last edited by Inkanyezi; 31st December 2012 at 11:51 AM.
Last edited by Mike Buckley; 31st December 2012 at 12:08 PM.
There are two main sources of "noise" in night time photography.
I assume that you are shooting at fairly high ISO levels, which means that in low light situations, you are going to have the gain (amplification) turned up and that will accentuate any sensor noise. This will be especially apparent in the dark areas of your image.
The other potential source of noise is from "hot" pixels, i.e. pixels that show up being brighter than they should be. This comes from leakage current in the sensor and the warmer the sensor is the more apparent the problem will be. If you are shooting long exposures (over a couple of seconds), the sensor circuitry is on for a longer time and you will get more impact from the heat.
As RAW images are unprocessed, none of the noise reduction algorithms in your camera that are used to generate jpgs are used, so noise will be more apparent in RAW files.
We're all suggesting different/similar things because you didn't give us much to go on.
I don't disagree with the other replies above, but I would 'toss into the pot' the following;
you do not crop excessively in PPAND
you have not under exposedAND
you are downsizing for web publishing from an image say 5,000 px on longest edge to say 1000 to 1600px on longest edgeTHEN
in the final image, it won't matter.
If you do need to noise reduce, try Neat Image
This is one of the issues which I sometimes address with the 2 Raw conversions from the same original file method.
As previously mentioned, using noise reduction can soften the image slightly (depending on the amount used). So I convert one Raw image using normal settings to suit the average scene and another with more noise suppression for the problem areas.
Then combine the two as layers with masks so the noise suppression is only applied to the required areas, which are manually chosen by editing the mask.
The same method can be applied to an edited layer (with mask) using any noise suppression software after Raw conversion or even on a Jpeg shot.
Going over problem areas with a suitable Blur Brush is another method which I sometimes use.
More info is needed, maybe a photo of the problem your having. Are you shooting in Auto mode, if so the camera I bet is setting a high ISO in trying to adjust for the low light. Just guessing here, tell us what setup your using and a photo of the problem.
ISO too high
Exposure - long exposure noise reduction on or off??
Plenty of dark areas in your photos (I presume) - means you are shooting to the left of the histogram - less data on the lfet than the right means inherently more noise/grain
There is plenty of info about how the raw data is used throughout the colour range. There is an exponential drop in the number of bits from right to left across the tonal range. There is a school of thought that we should always push our images as far t the right as possible without blowing any highlights and then pull the exposure back to a "correct" level during post processing.
Well I was shooting in low light (northern lights) ISO was set at 200, maual mode
When I get to my computer I will put the picture file in here
Last edited by slooky; 1st January 2013 at 11:52 AM.
I'll apologise in advance for being 'direct'.
Basically it was horrendously under exposed, so the Northern Lights were down in the noise and when you PP'd, the noise came up with the 'lights
EXIF says; Manual exposure: 20 seconds, f/6.3 at iso200 using the kit lens at 18mm on a Nikon D5000
Looking deeper into the EXIF data, I think you have;
Published in AdobeRGB, not sRGB
Camera Auto WB (4,100/-10)
In PP you have set;
Exposure + 2.65
Fill Light 67
Sharpness 25 (this may not be relevant)
Colour Noise Reduction 25
Possibly sharpened with a radius of 1
A lot of those things are going to bring up the noise.
In my view, given the circumstances, we need to deal with the noise first, with something like Neat Image, then set about recovering the exposure - this is far from ideal, but (bluntly) we're starting from a very bad place.
However, you did shoot RAW, so another processing of the RAW file might achieve a better result - I don't mind giving it a try if you can get it to me via DropBox or Mediafire.
I have applied Neat Image to the jpg and sharpened slightly, I think this is much better; flick between them in Lytebox at fullsize to confirm.
I am sure, from the RAW, a better result still can be obtained.
This is a classic case, I believe you'd have been far better off to shoot at 1000iso and f/5.6, because keeping the iso low to avoid noise just does not work if there isn't enough light.
Hope that helps,
Last edited by Dave Humphries; 1st January 2013 at 01:41 PM.
I am new to Raw but I always thought to shoot in low ISO equals less noise.
With what I processed made it a little less noise.
There is a lot of good information here, but I think one basic question might get lost. You started by saying that
A lot of the responses have to do with the "why is there noise" part of this, as opposed to the "shooting raw" part.When I've shot night photography in Raw, I sometimes get grainy pictures
Shooting raw will never increase the amount of noise in the base image. All images start out as raw. The only relevance is that if you shoot jpeg, the processing algorithim the camera uses to convert the image to jpeg may apply noise reduction.
This has nothing to do with shooting raw. Shooting in lower ISO will generally produce less noise if the image is properly exposed. If you underexpose, you will get noise. Google "expose to the right". The amount of noise is not reduced if you let in less light, but the amount of signal is reduced, so when you boost exposure in post processing to compensate for a weak signal, you are boosting the noise as well.I am new to Raw but I always thought to shoot in low ISO equals less noise.
Another issue may be the 20-second exposure. I don't know the sensor in your camera, but a lot of sensors will produce a lot of noise with exposures that long. On my camera, I use "long-exposure noise reduction" with long exposures for this reason. Unlike noise reduction in postprocessing, this does not soften the image. It just does a second exposure without opening the shutter to find the noise signature, and then it subtracts that from the image.
My suggestions for this sort of thing: expose to the right, and then pull exposure down in postprocessing if you need a darker image. And if your camera has it, use long-exposure noise reduction for captures longer than one or two seconds.
Just a little note on the long-exposure noise reduction.
As it is a black frame subtraction, you can still try it with the existing images:
take an exposure at the same ISO and exposure time settings, while leaving the lens cap in place,
then in your PP package subtract this image from the one to be treated, and develop the resulting image as usual.
Long-exposure noise contains so-called 'hot pixels', pixels that get more intense with increasing exposition times.
Those pixels are always in the same position (so this is not random noise). By taking an exposure under the same
conditions as the image, but with the lens cap in place, you get an image with every thing but the hot pixels as black,
the hot pixels will still be hot. So by then subtracting this black image from the original image, you remove the hot pixels.
Although the number and intensity of the hot pixels can increase with the age of the camera, this is a slow process.
So in practice you can take one black exposure and use it for a number of images. I prefer using that over using the
camera long-exposure noise reduction, as the latter doubles the time used for one image (not a problem when exposing 1s,
but when you get in really long exposures...). Do try to take the black frame at the same temperature as the images.
Even for experienced photographers, nighttime photography can be a tricky situation. Photos often look unfocused, blurry, or lacking crucial details, and many may not come out at all. There are some tricks, though, to taking spectacular nighttime photos with your digital camera, tricks that can be explained yet only completely learned through practice.
thanks everyone for the help!
Kevin - I see that you are using the kit lens for the image. I know the lens well (I have one) and at the 55mm setting it is rather slow at f/5.6; not a great lens for low-light photography. A reasonably affordable f/1.8 50mm lens would really cut down on your exposure as one of these lenses would be 3-1/3 stops faster and your 20 second exposure would be down to around 2 seconds.