01 July 2017

Difference between Digital Noise and Background Blur

Difference between Digital Noise and Background Blur
Blur can really mean different things in digital photography, but should not to be confused with unwanted graininess or digital noise across a digitally created image. Unwanted noise generally occurs when:
  • shooting in low light, when a digital camera's ISO setting is too high
  • shooting within the digital zoom range of a compact camera 
  • over-cropping an image

Unwanted blur
Out-of-focus blurred area(s) in an image that came about via unintentional camera movement, unwanted subject movement and / or wrong shutter speed settings when photographing movement - something you don't really want.


Deliberate blur
This will appear in areas of the image when the photographer attempts to blur certain areas of a composition / image. With foreground in focus, but the background deliberately blurred depending on the Depth Of Field (DOF) - distance between nearest and farthest object(s) of the composition / framing requirements ie. when isolating a flower from its immediate surroundings.

Deep vs Shallow Depth-Of-Field (DOF)
With a deep DOF more of the entire image will be in focus and its more likely to be used in Landscape Photography with smaller apertures of ie. f/11 - f16. With shallow DOF specific area(s) of an image is deliberately out of focus and can be applied in a variety of genres (Wildlife / Sport / Macro / Portraits) where the photographer deliberately wants to separate the main subject from the background - for this effect, larger apertures will be applied ie. f/1.8 - 5.6. 


DOF Aperture Test: Canon EOS 6D / EF 50mm f/1.8 STM lens - view>>

DOF flower series demonstration with Canon EOS 700D / EF-S 55-250 IS II lens - view>>



The visual quality of [deliberate] blur is also referred to as Bokeh
Bokeh: visual quality of the blur...The visual quality of [deliberate] blur is also referred to as Bokeh - Japanese for the out-of-focus aesthetic quality of the deliberate out-of-focus (blurred) area. a Wide aperture of i.e. f/1.8 - f/5.6 or so will be used (depending on the lens / optical distance from subject) to create the required out-of-focus effect.

See attached images below: white rose bud, the yellow rose and red rose bud with sharp / in-focus foreground sharp and background deliberately blurred (using wide apertures of f/5.8 and f/5.6). 

Lens apertures
In DSLR photography different lenses are used to create / select different levels of DOF depending on the lens aperture range, optical length of the lens and distance from subject. Different lenses / aperture settings will be applied  for different type of photography genres requiring blur effects at various focal lengths ie. for close-up / macro, portraiture or wildlife photography.  a  DSLR camera system is not necessarily required for creating deliberate image blur, a compact camera with a wide aperture lens with some optical zoom will also work. 

The images below were captured with apertures of f5.6 Yellow Rose (Non-DSLR Canon PowerShot SX40 HS with its f/2.7 - 5.8 35x telephoto zoom lens) and  f/5.6 Red Rose Bud (EOS 700D / EF-S 18-135mm f/3.5 - 5.6 IS STM lens / EF-S 55-250mm f/4 - 5.6 IS II lens).


Canon EOS 6D / EF 70-300mm f/4-5.6L IS USM lens / Extension Tue
Which Canon lenses?
Desired Bokeh-effects for close-up or macro flower photography can be achieved with a variety of lenses with wide apertures i.e. with fix aperture lenses such as Canon EF-S 60mm f/2.8 Macro USM or the EF 100mm f2.9 Macro USM prime lenses.

Any Canon DSLR camera body with either an EF or EF-S lens (or other compatible lenses) attached will generate deliberate background / selected blur, but the Bokeh quality will depend on the following factors:

  • Aperture settings (wider is better) 
  • Type of EF / EF-S lens (design and optical length) 
  • Depth of field of objects in the frame 
  • Distance to subject / lighting conditions 
  • Accessories used (extension tubes / close-up filters) 

Different lighting conditions
In all the images the objective was to keep the 'unwanted digital noise' across the frame as low as possible. For the "Yellow Rose' image, shot with Canon PowerShot SX40 HS, I used ISO 100 (in crisp early morning sun light) and the 'Red Rose Bud', shot with the Canon EOS 700D, I used ISO 400 with a Speedlite 430 EX II flash (in early morning overcast / raining conditions).

Canon EOS 6D / Canon EF 50mm f/1.8 STM lens
Photographers use blur for various shallow depth-of-field / artistic effects (image on the right - 'blue flower' and first image below - 'red mailbox' with Canon EOS 6D both at an aperture of f/2.8 with Canon EF 50mm f/1.8 STM lens. 

Last image 'bee on flower' was captured with Canon EOS 700D /  55-250mm IS II lens and Canon 500D close-up lens filter), Bee in focus, most of the flower blurred / out of focus, in a deliberate, aperture-controlled and planned way.

Optimal exposure settings
Just to come back to noise - you may have noticed that many of my own photos are not always shot in good lighting conditions. Most of my low light / long exposure DSLR photography shoots are done in Av mode, ISO 100 and apertures between f/16 - f/22 generating automatic shutter speeds of between 1 and 30 seconds.


I often use the camera's Manual shooting mode with similar aperture settings and Bulb Mode - the ability to have manual time control over shutter speeds during every single shot. A time to use this mode is when shooting fireworks. These exposure combinations together with the use of a tripod and RC-6 remote shutter release, almost entirely limits all unwanted  noise / graininess and unwanted blur. © Vernon Chalmers

(click to enlarge)
Difference between Digital Noise and Background Blur
Canon EOS 6D / EF 50mm f/1.8 STM Lens flash


Difference between Digital Noise and Background Blur
Canon EOS 700D   ISO 100  f/5.6  No Flash


Difference between 'digital noise' and subject / background blur
Canon PowerShot SX40 HS   ISO 100  f/5.8 


Canon EOS 700D ISO 400  f/5.6  Flash  Photo: © Vernon Chalmers
Canon EOS 700D   ISO 400  f/5.6  Flash 


Difference between Digital Noise and Background Blur
Canon EOS 700D   ISO 100  f/5.6  No Flash 


More Depth Of Field (DOF) Examples: DSLR / Non-DSLR / More Bee On Flower with Close-Up Filter