Introduction To Digital Photography

Why Digital ?

• Conventional Photos Can Be Scanned
• Film Cost

1. Digital "Film" Is Expensive But Reusable
2. No Processing Required

• Review and Playback Gives Immediate Feedback
• Permanence Of Digital Data Can Be Excellent ( e.g., Color Reference Is Preserved )

Exposure

• How Much Light Energy Does The Sensor Process ?
• A Function Of 4 Things:

1. Available Light... Which Is Hard To Control
2. Shutter Speed
3. Aperture Of F/Stop
4. "Film" Speed ( Sensor Again )

•  Generally, If Available Light Is Constant, Other Parameters Trade-Off

Exposure: Shutter Speed

• The Time Period During Which Light Is Sensed
• 2X Time Is 2X Light Energy
• Speed Usually Range From About 1 Second To 1/1000s
• Things Moving Faster Than Shutter Are Blurred ( and That`s Everything If You Move The Camera. )
• Under 1/30s, Brace The Camera ( e.g.., Use Tripod )

Exposure: Aperture , F/Stop, or T/Stop

• How Much Light Is Admitted ( Transmitted ) By The Lens
• Larger Aperture Is Smaller F/Stop number; 2X Steps F2, 2.8, 4, 5.6, 8, 11, 16

Exposure: Film Speed EI, ISO, ASA

• Light Measured By Electric Charge, Amplified, and Digitized
• Higher Is More Sensitive ; 2X Steps 50, 100, 200, 400
• Higher Implies More Amplification, Hence More Noise
• Moderate Underexposure Correctable With Higher Noise : Moderate Over Exposure Clips ( Looses Detail In ) Highlights
• Example Equivalent Exposures:

E1 50, 1/250s @ F2.8
E1 50, 1/15s @ F11
E1 200, 1/60s @ F2.8

Exposure: Film Speed & Sensor Noise

Exposure: Film Speed & Sensor Noise

Photographic Effects

• Focal Length

1. Shorter Means Wider Viewing Angle
2. Sensor Size Varies, So Quote 35mm Equivalents ;

Wide Angle Is < 43mm ( e.g., 35mm )
Telephoto Is > 43mm ( e.g., 135mm )

• Depth Of Field

1. Depth Of Field Is Distance Range That Is Sharp
2. Smaller Focal Length Increases Range
3. Higher F/Stop ( Smaller Aperture ) Increase Range

Depth Of Field

Depth Of Field ( Click Image To Enlarge )

Photographic Effects : Flash

• A Pulsed Light Source Synchronized With The Shutter
• Give Fast Exposure Without Enough Ambient Lighting, But Easily Yields Images Of Poor Quality
• Flash Has A Limited Useful Range, Images Look Flat
• Red Eye And Red-Eye Reduction Flash Modes
• Fill-in Flash And Flash With Slow Shutter Speeds
• Bounce Or Otherwise Soften Flash Lighting

Photographic Effects: Fill-In Flash

Photographic Effects: Fill-In Flash ( Click Images To Enlarge )

Image Capture: Sensor

• CCD Or CMOS Arrays With RGB Or CMYG Filters; Foveon R-G-B Sensor Stacks
• Analog Readings Converted To 8, 10, Or 12 Bit Digital
• Each Light-Sensitive Position Is Called PIXEL ( 1.5-3M Pixels Is Roughly Comparable To 35mm Film )
• Grain Is Mostly Noise, But Also Sensor Pixel Count
• Sensor Noise Is Less When Cold
• Sensor Noise Is Less For Fast Shutter Speeds

Image Capture: Sensor Filters

Image Capture: Sensor Filters ( Click Image To Enlarge )

Image Capture: Overexposure

Loss of highlight detail; possible local distortion of color

Image Capture: Overexposure ( Click Image To Enlarge )

Image Capture: Speed & Sensor Noise

Conventional Film has reciprocity failure problems;
for digital, very long times increase sensor noise

Image Capture: Speed & Sensor Noise ( Click Image To Enlarge )

Image Capture: Storage Media

• Types: CF, Smart Media, Memory Stick, XD,etc
• Capacity From 4MB To 1GB, With 50KB, To 2MB Per Image

Image Capture: Resolution  and Image Quality

• Resolution ( Of The Sensor ):

1. Some Sensor Pixels Are Used As A " Black Reference "
2. Can Interpolate Sensor Data To Any Image Resolution

• Image Quality ( Compression ) Settings:

1. JPEG Images Are Interploated And Compressed
2. JPEG Works Better With Higher Resolutions
3. Even " 100% Quality" JPEGs Are Imperfect

• TIFF Images Are Interpolated, Saved 24 Bits/Pixel RGB
• RAW Formats Save Sensor Data To Process Later ( e.g., 12-12 Bits/Pixel One Color )

Image Capture: Resolution & Image Quality

JPEG compression is effective for photos ( Click Image To Enlarge )

JPEG is more effective at higher resolutions
Both 100% and 50% 256x256 better than 100% 128x128

Image Capture : Color Balance

• Color Reproduction And Perception Is Tricky Stuff
• Use Manual White Balance Where Possible
• Can Fix Later ( Best Using RAW Format )

Color Balance ( Click Image To Enlarge )

Digital Darkroom Techniques

• Done With The Lights On, No Nasty Chemicals
• Can Do Some On - Site Using In - Camera Preview, Options
• Corrections:

1. Fixing Underexposure Increases Noise: Overexposure Clips Highlights, Information Is Lost
2. Adjust Color, Contrast, Dodge/Burn
3. Can Fix RedEye, Remove Unwanted Objects, etc.

• Cropping : Sensors Are 4:3 Or 3:2, Not 7:5, 10:8, 14:11, etc.

Digital Darkroom Techniques : Printing

• Various Printing Techonoligies:

1. Dye Sublimation: Highest Quality, Expensive And Slow
2. Inkjet : Good Quality ( With The Right Paper )
3. Laser: Fast and Cheap Per Print

• Does The Monitor  Match The Printer ?
• Want More Than 1000 Pixels Per Inch For Printed Image

Advanced / Specialized Darkroom Techniques

• Remove / Replace Backgronds
• Panorama Stitching : Create Larger, Hi-Res Image From Multiple Low-Res Images
• Correction Of Lens / Perspective Distortions: Can Undo Barrel / Pincushion Distortion, Logically Tilt The Lens, etc.
• Various Special Effects ( To Use Sparingly ) : Page Curl, Tiling / Mosaics, "Old Photo" Effects, etc.

 Non - Traditional Uses ( Of Images )

• Images For The WWW

1. Download Time Matters;  Keep Image File Size Small ( Generally, 640X480 Or Lower Resolution )
2. Use JPEG, GIF, Or PNG Compression

• Image Archiving :

1. CD Or DVD as "Archival" Storage... ( Many DVD Players Can Show JPEGs From A CD )
2. Can Easily Make Slideshows On Videotape, etc.

Non- Traditional Uses ( Of The Camera )

• The Camera Is A ( NTSC/PAL ) Presentation Device: 

1. Can Do Slide Shows Of The Umages
2. Upload And Then Show Any Images ( Often, Cameras Are Picky About Image Format )

• Visual Note-Taking: Photography Where You Parked, Notes On A Chalkboard, etc.

Thanks To Hank Dietz