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Exposure

DSLR  -  Beginner's most confused and must know information 
#Please note, almost all info is available on web, motivation is to convey the content in one short go. (refer: http://www.cambridgeincolour.com)

A mentor will make an impact with practical presentation, that will root firm in mind - be it physical or abstract.

Raw

Picture
Why Gamma ? 18% Eye/Camera different perception.
  • Unprocessed capture of data on sensor - raw data.
  • With user selected settings tagged along, to apply during display.

   Advantages of shooting Raw (Post Process)
  • White Balance, desired color temperature can be applied (before Gamma correction).                             Color temperature - Nikon applies warmer colors than Canon.
  • Color (Bayer) conversion accomplished with complex algorithms (better outside camera).
  • Apply desired Color space, using DPP Tool.
  • Apply desired Gamma correction i.e. brightness/contrast selection.

   Gamma
  • Camera is a Linear recording device. Eye interprets Light in a Non-Linear function.
  • 18% Linear illuminance is perceived by Eye as 50% Grey (but camera records it as 18%)
  • Graph on left indicate detected light, that would apply to output of an Analog/Digital converter to create RAW.
  • Humans cannot differentiate Highlights (allocate here few bits) and sensitive to Shadow values (more bits required for preserving more details)
  • Non-Linear bit allocations and encoding is Gamma correction ( offer uniform gradation in perception and efficient use to available data bits ).
  • Gamma is relationship between a pixel's numerical value and its actual luminance.
  • Gamma 2.2 used by Adobe RGB and sRGB.
  • Vout  = k. Vin ^ Gamma  : Gamma<1, the line arches upward (Graph), Gamma>1, the line arches downward.
  • Image Gamma is used in Encoding process -   (JPEG encoding from RAW, Image gamma of 1/2.2)
  • Display Gamma is used in Decoding process - (CRT/ Video card a display gamma of 2.2)
  • Image gamma is usually specified by a color profile.
  • No color profile is embedded, then a standard gamma of 1/2.2 is assumed, eg: GIF, PNG.

   Some facts
   # Canon S5IS saves at 95, Canon 550D saves 97 quality for JPEG.

 Raw 14 - bit A/D sensor data bits per stop

Picture
Only for estimate/understanding (not accurate)
   Advantage of 14-Bits in Canon 550D
  • Digital sensor offer a dynamic range, of 5 f-stops. (Human eye is capable of 8 - 14 stops)
  • Due to Linear function of camera sensor, more bits in for Bright Highlights, and few bits in for dark tones.
  • Shadow regions have more bits (better details) to modify in RAW (14bit) than Jpeg (gamma applied on 8bit).
  • Hence, better detail and quality is preserved in Raw stage.
  • Further processed as 16 bit image with 65,536 levels (rather than 8-bit image 256 level limiting JPG).
  • SNR is important, noise is critical in Darkest tones, ISO 100 is recommended, Nikon D90 beats Canon 550D here.
  # As processor speed performance improves, even more bits are possible challenging for better SNR - 'Digital camera body / sensor' are on evolutionary track, better invest on Lens, unless and already own them.

 CCD sensors are claimed to have better dynamic range of sensing Light threshold upto saturation almost double the general CMOS capability, 
 Purpose of using CMOS is cost effective and Low power consumption, moreover a new technology so more pitfalls.
 Canon Powershot S5IS was last in that series for using CCD sensor.

  Sequence in editing RAW (my preference)
  • Choose the color space.
  • Check noise - Apply Luminence/ Chrominence noise reduction, if desired with Sharpness minized.
  • Now improve sharpness for the loss due to anti-aliasing filter, results are good after noise correction.
  • Apply sufficient sharpness, do not let halos appears at transitions or discontinuities.


Exposure

Picture
(Hue/Saturation/Light) - HSL plot
   Exposure in other words may term as brightness recorded.
  • Over-exposure contrast is lost in highlights.
  • Under-exposure contrast is lost to darkness.
  • Correct Exposure (Balanced) preserves maximum details and information.
  
   Shooting at correct exposure is important and useful for color retention, as seen with the HSL cylinder 
  • Over exposure will turn your colors to white. 
  • Under exposure will give away color to black.
  • Correct exposure will retain color information, saturation is in editor's control. 

   Metering
  • Camera's built-in Light Meter can fail, as it measures Reflected Light, instead of the Incident Light.
  • Correct exposure is possible by compensating the exposure suggested by Camera's built-in Light Meter at its limitations/ failures.

   Standard Tools for correct exposure
  • 18% Grey Card
  • Light Meter

   Alternative Tools 
  • Histogram - show gamma encoded data values for selected exposure.

   Other Realities
  • Many an occasions - captured image do not match with what your eye experiences through viewfinder of DSLR, yes - dynamic range of Eye is far superior to digital sensor of consumer DSLR, the outcome brighter object render very bright and dimmer object as dark, lacking same details far from the beauty experienced by our eyes.
  • Do not expect to photograph every thing - what we see, camera may not see, show your understanding in choosing what your companion finds good. Humans the only species, who makes best use of tools :)

   Books to Refer
  • Understanding Exposure by Bryan Peterson.

Lights

refer: lighting 


Classic methods-Rembrant Light
-Split Light
-Broad Light
-Butterfly Light-Loop Light

Color Spaces

Picture
Color gamut for ProPhoto RGB /Adobe RGB /sRGB.
   Canon 550D supported color spaces for JPEG shooting  
  • Adobe RGB
  • sRGB

   A color space - has a color gamut (is a certain complete subset of colors)
  • Adobe RGB - encompasses more colors visible to eye.
  • sRGB - offers more gradient within available limited few colors.

   
Printing
  • Adobe RGB - suitable for Printing (may look dull in Web)
  • sRGB - suitable for  Web (Not for printing)
   #  Shoot in RAW to apply desired color space.
  • In color printing, subtractive color model is employed like CMYK color space, 
  • Some colors in sRGB are not available in CMYK space.
  • Identifying the colors in an image which are out of gamut in the target color space during processing is critical for the quality of the final product. 

          The CMM can deal with this problem, ICC profiles offer,
  • -Relative intent, handles out-of-gamut by clipping (burning) these colors to the edge of the gamut, leaving in-gamut colors unchanged.
  • -Perceptual intent, smoothly moves out-of-gamut colors into gamut, preserving gradations, but distorts in-gamut colors in the process.
           http://www.normankoren.com/color_management.html

   [ I never tried to print, below info might help to explore further ] 
   Care to configure printer and Adobe Photoshop
  • select the source space
  • select in print space, 
          - Color Profile
          - Paper  Type
  • Go to printer properties, set Printer profile (.icc/icm) settings to OFF
          (To avoid re-doing the job)

  Books to Refer 
  •  Mastering Digital Printing, by Harald Johnson


Hue - Applications of Hue - Black & white Images

Picture
 When an image is desired to Converted into a Black and White Image 
 Always the Subject is Desired to look distinctly bright than its surroundings
 Take color image modify its Hue distribution favouring the bright 
 Then covert the image to grey scale 

Picture
Picture

Lens - Abberations and Alternatives

Picture
Optical abberations and remedies
  Essentially important to know about Lens to identify to satisfy requirements or have remedies.
     - What you need - Macro, Telephoto, WideAngle.
     - What to own to fulfill your need - Prime, Zoom, Fast Lens, USM, Rear Focus, Image Stabilizer.
     - At least know how to overcome weakness of your lens to attain your need.

  Category
  • Macro Lens - designed for Closeup of miniature subjects astigmatism is best managed.
  • Telephoto Lens - Telescopic Lens, narrow angle of view coverage for Far off subjects.    
  • Wide angle Lens - Wider angle of view coverage, for scenery, landscape - extreme is a Fish Eye lens.

   Type and Design
  
  • Prime Lens - Fixed focal Length Lens, with only focus ring - Best corrected for most aberrations for a Focal Length.
  • Zoom Lens - Support a wider focal range, usually abberations are not very well manageable, need not change lens frequently.
  • Fast Lens - Large aperture typical Gaussian design may be employed, supports faster shutter speeds, shallow DOF for great Bokehs. 



















Tools not to be ignored in DPP for Canon

The distortion due to kit lens can be corrected both pincushion and barrel distortion forms 
Chromatic abberations are also effectively managed.
Choose your Lens considering for your eclectic interest

Bird Photography

Picture
In Flight - Painted Stroke - with Canon S5 IS
 
Beauty in Bird Photography with focal lengths of 200-300mm, is you might have learnt to make the bird feel comfortable
- Identify place, pattern of their movements.
- Never use eye contact, follow it through your view finder, 
- Don't not make quick moves take yourself into slow motion, 
- Do not move straight towards your beautiful bird, make it look tangential. 
- Hiding is critical if you are too close, a suspicion will drive it off. 
Few birds usually rest pluming their feathers, once they find the place comfortable say after 10:00am / afternoons.
so the point you need to stay over in the place for a long time, and appear to involve in a work of your ownfairly you are not considered as major distraction,  

Settings in my preferences with 550D while shooting most birds.
  • Load on Sigma APO 70-300mm zoom, ISO 100/200, f9/f10/f11 preferably on Tripod when situation permits.
  • Turn Off Auto Light Optimizer (for Flash control - in case opted to use) 
  • RAW (To leverage on exposure curve adjustments to bring details from shadows, suppress Highlights) 
  • Continuous Frame shoot drive (Prepared for bird taking to flight/eating, quick changing moments)
  • Position subject to center (Center part of lens tends more sharp, and aberration free) 

     Birds alight on branches
  • Enable the central AF point* (being more sensitive & accurate)/ or other single AF point orient it on Subject.
  • ISO 100 (TriPod) /200 (MonoPod)
  • Mono/Tripod
  • Mirror Lockup at 300mm, with 2 sec timer -or- external wired Trigger. (depending on shutter speeds in use). 
         *With multiple AF points active, leaves in foreground may defocus, when your subject is close remember your DOF is really shallow.

    Birds in Flight
  • Enable all AF point (if Background is far off).
  • ISO 400(For motion blur)/ 800/ 1600 (Sharp + Extreme Noise).
  • Elbow supported/ Elbow+Knee supported (guessing the bird for a take off)

 Guidelines:
 1.  Fill your frame with Subject - (First step to bird photography)
 2.  Details are critical - use sweet spot whenever  possible (Tripod helps).
 3.  You need a hide to be close, to satisfy (1) - most of the time.

 Handheld Image Blur: 
  • Practice to press the shutter after you exhale. 
  • Using Back-pack as a prop up.  
  • Lean to a pole,  support elbow to the body.  
  • Prop on car window (car was a wonderful Hide too).    
     (Quick release plate is always attached to the body)

  Sharpen the image on Raw
  Capture sharpening
   Blurring is caused by the camera sensor's (in addition to your camera's lens)
    1. Demosaicing process: A color filter array (CFA, e.g. Bayer filter) is a mosaic of color filters in front of the image sensor, color subsampling result in aliasing.
    2. Anti-aliasing filter (optical lowpass filter /blur filter) is employeed to minimize the aliasing effects.
    Demosaicing Algorithms for Canon
    dcraw - linux
   Output sharpening
   Settings customized for a particular output device (print/monitor), and is applied at the very end of the image editing workflow.

   Refer: http://www.cambridgeincolour.com/tutorials/image-sharpening.htm
 # Images without story, is no attention catcher..... deliver content... demand attention. 

Getting sharper Images with what is available...

Picture
Tripod is just a must.
 What one expect to get sharp images ?
  • Quality L series lens - well corrected for aberrations.
  • Fast Prime Lens - enabling good shutter speeds and advantages of fixed focal length.
  • Image stabilizer for Low light
 
 Too Expensive..... It is a real opportunity before you, to learn small habits and build up your capabilities.

  • Exploit the sweet spot of your Lens, Its your job to know it - refer MTF charts.
  • Use Tripod - enabling more light through slow shutters. (Get rid of handshake blur, when ever possible)
  • Practice, develop and discipline yourself to properly handle the tools - Camera, Tripod.
         (........are some of the suggestions in short, bestowed by my mentor, though I attained a little - they work miraculously well)
 As a beginner, options/selection for a Tripod / Monopod is based on criterions below, available in various ranges and specifications.
some pointers to look for
1. Compact and weight     -Steel/aluminium/carbon   -(convenience)
2. Steady and solid             -Construction/design         -(sharp images)
3. Expanded Height            -usability                               -(convenience - standing)
4. Compact  Height             -usability                               -(convenience - sitting)
5. Mount capacity                 -Camera weight support   -(effective mount system)
6. Mount flexibility                 -Roll, Yawn, Pitch               -(ease of orientation)  


Nature Shoot

Picture
Clouded hill terrain - minutes after Sun rise - kodaikanal.
Photographing is all about Light - Paint with Light and do it right, 

Sun is one of greatest photographer's delight, spectrally so good, there are favorable times for sunlight to take advantage, to make your graphs all look so brilliant !!!  

So Care to plan, to be at shooting site in time, usually on those clear Sub-continent sunny days,
Summer Mornings  - 5:30am* - 8:00am    Winter Mornings  - 6:00am* - 9:00am
Summer Evenings   - 4:00pm  - 7:00pm*  Winter Evenings  - 2:30pm  - 6:00pm*
*Dawn or Dusk.

In short favorable times allow favorable front light for your subjects, especially in Latitude ranges of South India, midday we do have lots of light, but light from Zenith is no much help, we have limited opportunity of a day, than what the higher latitudes can offer. 

Panorama Shoots

  • Use a Good stable Tripod, Such that the Mount pan across comfortably - without adding varying inclinations effectively spoils during merging.
  • Shoot in Manual mode to avoid exposure changes with changing scene brightness which could prop up discontinuities for stitch.
  • Eliminate close objects they introduce parallax in consecutive pan images.
  • Lens ? 


Portrayal

Picture
Color Temperature - Representation
  • Diffused Light brings in softness, more visible features. Some naturally diffused light sources are common with Window light, Door curtains, conjunction points of 3/4 tree cover and 1/4 open grass fields with Sun.
  • Color Temperature dramatically changes the impression of image, usually Auto White Balance makes a good choice, photographer always have a choice to choose with various color temperatures available (Daylight, Cloudy, Shade) mid-range 6000K -4000K works well with my usage.
  • Background contrast, Eye is more sensitive to luminance than color, each color has a luminance, choosing a background in color which is in contrast with subject color usually proves image enhancing.
  • Preferably, work out to frame your composition - cover 5 Stops of dynamic light range only, especially in choosing the backgrounds will help, this is a limitation of system - now work to hide its weakness.
  • Frame to exclude clutter and High-lights as much as possible.
  • Bokeh creation using widest aperture, renders your image softer and background High-light smudge out as circles gives in a pleasing Bokeh /Blur, Telephoto lens is wonderful.
   #     A wonderful analogy from my mentor teachings:  For your diffusion system to be effective, in rendering details soft, 
      -   Your diffused light source must be larger than your subject (e.g. Face alone).
      -   If your diffusser is large but placed far of subject - it works as a point source, Bring it closer.


     For successful portrait artists, capturing personality is the end goal. 
     Capturing personality is an exciting challenge, but it is not impossible. 
     All it takes is attention to detail, and genuine care about your subject as an individual.

     Watch your subject as you interact with them. 
     Find out their little tendencies, find these hidden signatures, 
     You will be empowered to capture your client’s personality like no one else.
     If you truly want to highlight your clients’ personality, you will draw them out of their skin.

     Body language: The key is simply to learn to observe quickly, and respond in kind for the shot.
     (extract from Digital Photography School - guest post)



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