Long Exposure Night Shots Noise HELP

[marcdpalmer]

Hi all,

Please take a look at the pic's below. I have attached the pic and the exif data. There seems to be loads of noise in them both. To me anyways. Im not too worried about the composition, more the settings. These were my 1st attempt at long exposure nights involving the sea, and I was pretty unimpressed with the amount of noise. The lens used was a Tamron 28-75 2.8. Can anyone please give me a few tips that would help me reduce the noise...

Thanks

M

[marcdpalmer]

The 2nd shot.

Thanks

M

[Bill Boehme]

Underexposed areas of an image are always noisy. The reason is that the extremely small amount of light falling on the sensor is barely above the inherent noise in the electronics ... some of which is due to amplification and some that is characteristic of the sensor. Every individual sensor element* has a slightly different sensitivity to light, maximum charge capacity, and noise floor. This difference in element-to-element behavior also adds to the noisy appearance. The noise problem is worse in dark areas because the ratio of signal to noise is lowest.



* sensor elements are often referred to as a pixel, although they are not pixels in the same sense as image pixels because each one only records one of the three primary colors whereas an image pixel is full color.

[Bill Pham]

sorry can't help about the noise issue but i like the second shot better. so i ran it through noiseware and it's come out looking fine. hope you don't mind. if so i'll take it down. and usually when doing nite shot i use iso 100.

Bill

[luigis]

f32 and f16 don't make any sense in a Canon 30D for those shots, Diffraction makes the image quality terrible and that increases the noise. You should be shooting at f8 or f11 and the DOF will be enough and the IQ much better. After doing that correction use ISO100 and overexpose the shot as much as you can without blowing any highlights, then just adjust the RAW exposure down to the level you want and you should have a lot less noise in the picture.

Luigi

[Bill Boehme]

Also, before posting an image on the web, it should be converted to sRGB since most people do not use browsers that are color managed. I noticed that both images were saved with AdobeRGB as the embedded profile.

Since your questions about the images are technical, you can probably get much more in-depth feedback on the RAW, Post Processing, and Printing Forum.

p.s. Luigi is right about the aperture. You could probably even shoot wide open on those images and set the focus at the hyperfocal distance.

Also, I do not think that it is a good idea to include bright lights in a long exposure.

[marcdpalmer]

Thanks for that guys.

M

[kirkt]

You can do a few things to help with the noise that will ultimately occur in such shots. You can use a noise reduction app like Neat Image or Noise Ninja to help reduce/suppress the noise. If the noise is truly random, you can also shoot a stack of images and combine them - in PSCS3 (is use the Extended version, so it may only be in the Extended toolkit) there is a module for Image Stacking. This is text from the PS Help, regarding image stacks:


About image stacks (Photoshop Extended)

An image stack combines a group of images with a similar frame of reference, but differences of quality or content across the set. Once combined in a stack, you can process the multiple images to produce a composite view that eliminates unwanted content or noise.

You can use image stacks to enhance images in number of ways:

To reduce image noise and distortion in forensic, medical, or astrophotographic images.
To remove unwanted or accidental objects from a series of stationary photos or a series of video frames. For example, you want to remove a figure walking through an image, or remove a car passing in front of the main subject matter.
Image stacks are stored as Smart Objects. The processing options you can apply to the stack are called stack modes. Applying a stack mode to an image stack is a non-destructive edit. You can change stack modes to produce different effects; the original image information in the stack remains unchanged. To preserve changes after you apply the stack mode, save the result as a new image, or rasterize the Smart Object. You can create an image stack manually or using a script.

The idea is that the randomness of the noise will get averaged out of a stack of similar images because the random noise present at a particular pixel location will become small compared to the actual signal that gets summed at that same pixel location over all of the images. In both of the images that you have posted above, the JPEG artifact is much more prevalent than any noise, so it is difficult to assess the specifics of each image. However, either technique will help in combating noise. Also, your camera may have a noise reduction function for long exposures - check your manual (i am not familiar with the 30d).

Finally, if you really want to get into it, take a shot of the inside of your lens cap (put the lens cap on the lens and open the shutter at your specific iso and shutter speed) and take a look at what you get. You should see noise and this noise can be useful in profiling the noise you might expect in your long exposure images. You can then test your noise reduction techniques on these images (for example, take 10 shots of your lens cap and stack them to see how much reduction there is, etc.). image stacking requires that the scene be fairly static, because changes in the images are being suppressed, by virtue of the technique itself. This may be an issue the longer you need to leave the shutter open for each shot (ie., there is more time elapsed between the first and last shot in your series, and more time for clouds, stars, the moon, to move, etc.).

Also, and sort of unrelated, make sure you cover the viewfinder when performing long exposures so that light does not enter through the back door. That's what that seemingly useless little black rubber thingy on the strap of your camera is for - covering the viewfinder opening. Opening up the aperture and using the hyperfocal distance, as suggested above, will also reduce the amount of time necessary to have the shutter open for the same exposure (or it will permit you to bump the ISO down).

Hope this helps.

Kirk

[marcdpalmer]

Guys, thanks again. I already cover the view finder when taking long exposure shots. It certainly stops the amount of light getting in. I took 2 shots on the same night, one straight after the other, one with a heavy cloth over the VF and another without. Serious difference.. Thanks again for the tips.

M

[PhotosGuy]

I already cover the view finder when taking long exposure shots. Do that if it makes you happy, but you really only need to do that while your taking an exposure reading in M mode without your eye at the viewfinder, OR when the cam is on Av, Tv, or other auto mode.
No light from the viewfinder comes in during the exposure.

Best to stick to even # ISO settings, too. Like 100,400. The cam interpolates the in between readings & some say that causes noise.

[Colorblinded]

I agree it's better to err on the side of overexposure. Also, like kirkt mentioned you may want to turn on in camera noise reduction if you didn't have it on. I also agree with him that I see overall softness and compression artifacts as the biggest problems in these images, not noise itself.

To reduce noise though turn on the noise reduction as mentioned. Also, shoot at ISO 100, the base standard ISO for your camera, rather than at ISO 250. That should improve noise performance a bit. You may also want to look at using aftermarket noise reduction like noise ninja on your computer to process the image and remove some more noise. There are a number of programs designed to help reduce noise though, I just don't know what else is out these days because I haven't used a program like that in several years.

Finally, as someone else mentioned, if you push your exposure towards the higher end (assuming you can or it won't affect the appearance of your image in a negative way) then you can pull the exposure back in RAW processing and that will lower your noise as well. The most noise is always contained in the darker tones of the image.

[Bill Boehme]

Best to stick to even # ISO settings, too. Like 100,400. The cam interpolates the in between readings & some say that causes noise.

It depends on how the "in-between" ISO values are done, but using "interpolation" doesn't make sense since that, by definition, involves calculating two different exposures.

Unlike film which can be obtained in a variety of sensitivities to light, a digital sensor can't change its output except by electronic means in post capture processing. On a CMOS chip, the stored charge at each sensor site is buffered and converted to a voltage by the on-site isolation transistor and then amplified before being processed through the analog to digital converter. The amount of amplification is a function of the selected ISO setting. The only situation in which I can envision lower quality images for "in between" ISO values would be if exposures at those values were done post digital conversion. I don't know the answer, but treating the "in between" ISO values differently would only make sense if there are other constraints such as input interface bits to the processor that would limit the number of analog gain settings and any additional values would then need to be done digitally.

[PhotosGuy]

interpolates Maybe a bad choice of words. I've seen threads on it somewhere, but don't have in between settings so didn't pay that much attention.