DPP - Digital Image Qualities - Exercise 3 - Noise
I often use Ken Rockwell's site for information about camera's and lenses. He has a nice easy way of explaining things and in the most errs on the side of cheapness with quality. This can be very handy when looking to buy items second hand
The link below at the top of the page shows an interesting comparison between two images taken with the same Nikon D80 but one at ISO 100 and one at ISO 3200. Ignore the rest of his post if its only ISO you want to learn more about:
http://kenrockwell.com/tech/dslr-comparison/index.htm
With many camera manufacturers' squeezing more and more pixels onto the same size sensor then aside from larger images, image quality can deteriorate when out of prime image create conditions, normally lower light. Larger pixels will retain more tonal differences and be less susceptible to noise. Despite modern technology you only have to look at social media websites with images taken by camera phones in low light to see the noise that can get recorded in images.
I use a D700 which is a full frame camera but with a sensor recording just over 12.1mp it could be considered a low number by today's standards but at the same time is also one of the reasons its a great camera in low light.
I've found from previous experience that my D700 can produce usable images with ISO at 3200 but of course each circumstance when taking an image can be different and so results may differ also. See a previous log entry I have made:
http://warrenjonesphotography.blogspot.co.uk/2013_04_01_archive.html
In line with the exercise I've set up a simple shot of a mechanical hand in the bathroom where there is dappled daylight from an overcast day and utilised both a white and coloured background.
All images have been taken at f/8 with a 50mm lens. I've used the jpegs rather than processed the RAW files. I've taken a series of images starting at ISO 200: All images below are unaltered aside from reducing width of each image to 1000 pixels and reduced image size to around 100k for space reasons.
ISO 200
ISO 250
ISO 320
ISO 400
ISO 500
ISO 640
ISO 800
ISO 1000
ISO 1250
ISO 1600
ISO 2000
ISO 2500
ISO 3200
ISO 4000
ISO 5000
ISO 6400
ISO 8000
As you'd expect the shutter speed started to increase with the camera in Aperture priority at a fixed f/8 when the ISO was increased. Increasing the ISO allows the sensor to be more sensitive to light. Shutter speed appeared to even out around 1/10s then become faster at slightly larger intervals to compensate for more light being received by the sensor.
At this size of images its difficult to see much change in noise. However zooming in on the image at ISO 8000 the image appears to be more grainy as a result of the image noise. This is much more noticeable in the shadow area bottom right on the images.
What I also noticed, partly by accident is that the file sizes of the original images increased as the ISO increased. This varied at early ISO from 80kb up to about 400kb at ISO 8000. Michael zang in the following web page suggests that this is as a result of poor file compression with noisier images:
http://petapixel.com/2009/12/22/why-higher-iso-leads-to-larger-file-sizes/
Image noise and its relation to ISO is explained in much more detail in the following Wiki page:
http://en.wikipedia.org/wiki/Image_noise
In this wiki it mentions banding noise, similar to shadow noise which can be introduced in brightening shadows. My tutor commented on this in one of my images for Assignment 1. The wiki page also mentions Anisotropic noise variances in the columns or rows of pixels subject to the cameras orientation
Exercise Learnings
a) Increasing ISO allows the sensor to become more sensitive to light. This allows for faster shutter speeds
b) When using a camera hand held, increasing the ISO may enable a sharp image to be captured, even if more noise is in the image. Its easier to remove noise from an image, subject to limits where as an out of focus image caused by camera shake is likely unable to be saved by sharpening
c) Noise captured within an image can cause file sizes to increase. This appears to be as a result of file compression in jpeg being more difficult to process with noisy images
d) Noise appears to generate and increase more noticeably in the shadowy areas of an image
e) Noise will generate less noticeable on camera's with larger pixels e.g. cropped sensor with 12mp will have smaller pixel sizes than a full frame sensor with 12mp. For example this could mean a full frame camera at ISO400 produces less noisy images than a cropped sensor at ISO 100
f) Noise in images will become more noticeable / get worse as the image is increased. This one of the reasons why images taken on mobile phones seem OK and sharp when viewed on a small camera screen can look very noisy when viewed on computer screen. This is very evident when looking at images on social websites
g) Acceptable noise v intended image size v noise reduction processing. These are all considerations for the photographer and his/her tolerance for noise in the final image
h) There are various options of noise reduction through software. I personally use Imagenomic Noiseware. Below is an example of its capabilities
This is a zoom crop of the image above at ISO 8000 where I've cropped to display the noisy shadowy area:
ISO 8000 - NO noise processing
The noisy elements within the image are quite noticeable
ISO 8000 - WITH noise processing
In the processed image above noise in the image has been reduced but as a result there does appear to be some smoothing in the image and perhaps some detail lost, look particularly at the wrinkles in the un-processed image then look for these in the second image below
Which image is better? No doubt its permutations of my exercise learning g) above. An experienced photographer will understand what ISO limit produces a usable image for a specific size and at what level of digital post processing will be least disruptive or least noticeable in the final image
There is no doubt a number of good reasons why studio photographers, sports photographers and landscape photographers may use different types of camera.
Nikon D800 - Large images with lots of detail but less good in low light conditions. Great for Studio Photographers where lighting is perfect
Nikon D4 - Medium size images with very good detail. Smaller images mean faster image processing to memory card, sensor size v mp on sensor also allows good images in low light. Great for sports photography.
D700 - Small size images with pretty good detail. Small images can mean fast image processing with extra battery. Sensor size v mp on sensor allows for very good images in low light. Great for landscape photography
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