DPP - Part 2 DR Digital Image Qualities - Exercise 4 - Your camera's dynamic range

DPP - Digital Image Qualities - Exercise 4 - Your camera's dynamic range

The instructions for this exercise was to find a scene with a distinctly high dynamic range.

In addition to the front of the house light by winter sun I've also included an A3 sheet of white card and an open doorway.

The purpose of this exercise is to determine the dynamic range of the camera, in this case I'm using a D700.

I'm using the camera in Aperture priority and have left the camera matrix metering. In the image below I've spot metered on the brick wall just below the lantern. 

I've not needed to make an exposure compensation as the camera has correctly metered at the point just before highlight clipping occurs. This is borne out for the blinkies in the camera and confirmed when looking at the RAW file in CS6


Aperture of F/8 used a shutter speed of 1/500

This is the jpeg above. The image overall appears exposed OK.
I've not needed to make an exposure compensation as the camera has correctly metered at the point just before highlight clipping occurs. This is borne out for the blinkies in the camera and confirmed when looking at the RAW file in CS6



Aperture of F/8 used a shutter speed of 1/2500

This is the jpeg above. Metering for the card the camera has reduced the overall exposure so that the card is not blown out. To achieve this the camera has used a shutter speed of 1/2500, 5 times quicker than the image above.  The result is that the image in general appears under exposed elsewhere.


Aperture of F/8 used a shutter speed of 1/250

This is the jpeg above. Metering for the dark elements in the door way the camera has selected a slower shutter speed which has resulted in all other areas of the image being over exposed

Using the following website I was able to quickly calculate the dynamic range between the 2 exposures, based on the shutter speed difference, was 3 1/3 stops. The camera when not using spot meeting selected a shutter speed of 1/500 as the average exposure which is a difference of just one stop from 1/250.


Zooming in on the first image using the RAW file and getting to 100% zoom crop on the white card using the eye dropper I can see how good the camera has been in its exposure, as mentioned above. The image below is recording, outlined red:
Red       = 251
Green   = 251
Blue      = 252

Continuing the exercise bringing out the detail from the shadows using the exposure tool its maxed out giving a dynamic range of 6.5 stops

Going on to the website DXO Mark, which is a well known company running tests against a vast number of cameras and lenses I found for landscapes the camera is tested, at least for landscapes, per the test to have a dynamic range of 12.2 EVs

http://www.dxomark.com/Cameras/Nikon/D700

As this is an independent company rather than the manufacturer I'm assuming these tests to be accurate but who knows, perhaps something went wrong for me with this exercise

There is some interesting information here on this website which details some interesting facts about the dynamic range and low light sensitivity of the human eye and comparisons between the eye and a camera's abilities:
http://www.cambridgeincolour.com/tutorials/cameras-vs-human-eye.htm

The aperture in the human eye is the pupil and the eye can quickly scan the view in front of it focusing and adjusting across the scene and the brain will also fill in any missing gaps. Alas the camera has just the RAW image to show for it. As I mentioned in an earlier exercise a big disappointment for amateur photographers can be the realisation that the camera cannot always copy what the eye sees then again like the eye, it needs some help in being told what element of the image it should focus on and adjust to.

DPP -Part 2 DR Digital Image Qualities - Exercise 3 - Noise

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