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Digital Photography

Digital Photography

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Digital Photography

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  1. Digital Photography Photo Organization September 13

  2. Checkpoint • Signed Camera Check Out Form • Brainstorm notes • Think about what types of images you may take • Think about when you may take them • Think about how you may edit them in class • Keep in mind that you may take several thousand photos this semester, and may have several saved versions of each

  3. Organization • Let’s discuss what we came up with • We can always use somebody else’s ideas for this, if we like it better than the way we did it! • You guys have it much easier for organization than past classes, because Adobe CS2 offers a lot of cool stuff • Note: only the black computers have CS2, not the silver ones

  4. Adobe Bridge

  5. Adobe Bridge • Views: • Thumbnail • Filmstrip • Details • (Versions and alternates) • For all these views, you can change size of image displayed

  6. Metadata File PropertiesIPTC Core - Standard bunch of metadata for filesCamera Data

  7. Keywords • Some pre-defined keywords, but the user has complete freedom in choosing Keyword Sets and individual keywords

  8. Ranking • Built-in easy way to rank images • Select an image and the dots beneath the image are selectable and change to stars, based on your choices

  9. Other Features • Rotation of images • Labeling • Filtering (based on rank or labels) • Find - can base it on several criteria • And more!

  10. Lab Time • You can begin to use Bridge • To set up your organization structure • To rotate any images • To identify and delete any “out-takes” • To assign rankings, keywords, etc • Have fun, but begin a solid structure that you can build upon

  11. Homework • Read Chapter 2 • We will discuss tomorrow & Thursday in class • It is difficult material!

  12. Light and Sensors Lecture 04 September 14, 2005

  13. Entering complex material… MDP Chapter 2

  14. Photography is about light • Photography = “to write with light” • So we have to understand a little about light to understand how cameras work

  15. How we see light • White Light (from the sun) is made up of colors, and each light has a certain wavelength • Light waves are either reflected, absorbed, or transmitted – which is determined by the object that the wave hits • The color we see is based on the type of light sent to our eyes  An apple is red because it reflects red light • For an objects to be black, all wavelengths of light are absorbed, no light is reflected • The primary colors of light are red, blue and green (we will talk more about this later) http://imagers.gsfc.nasa.gov/ems/visible.html

  16. How a camera takes a picture • A camera is like our eyes – to “see” color, it must be able to capture the light that is reflected from objects • Reflected light enters the camera – passing through the lens’s glass (which may have many elements) • This light gets focused onto a sensor • The sensor is sensitive to light, so it captures the light and stores it – creating the image

  17. What happens inside the camera

  18. After light hits sensor • Allows viewing of image on viewfinder or LCD • Viewfinder • can roughly match what sensor sees • Could be like a mini tv • Might be a reflection of the light from the lens • Push the shutter release button – the shutter opens/closes for a period of time • Camera may autofocus, lock exposure, cause flash to fire, etc • Digital information is stored on memory – the speed that it takes to write the information to memory depends on size of image, type of compression & compression ratio, and speed of media)

  19. Sensors and colors • Sensors can’t see colors – they can only collect the brightness of the scene • Colored filters are used to limit range of light for each pixel • So each pixel reads a value for the red, green, or blue to define the final color – sometimes only one color is read, and the others need to be interpolated • Different sensor types have different ways that they deal with this limitation

  20. How a sensor works • The sensor is sensitive to light, so it captures the light and stores it – creating the image – how does this work? • Sensor is made of millions of individual light sensitive pixels (diodes) • This sensors are arranged in a grid, or array • Each pixel collects a charge proportionate to the intensity and amount of light • Pixels translate light into specific voltage values • The strength of the charge corresponds to the brightness of the pixel (up to a certain point) • A pixel can only hold so much charge, if too much builds up, it could overflow to neighboring pixels – a process called blooming – proper exposure will eliminate most blooming, if in doubt, underexpose the image • Some sensors have mechanisms built in to minimize effects of blooming

  21. What happens with the charge? • Light has been collected as voltage (charge) • Voltage information has an infinite amount of variation, smooth transitions • This is called ANALOG information • The camera needs the information to be in discrete digital numbers to store the picture • So the sensor (or other circuitry) has to perform analog to digital conversion

  22. Digital Data • The digital data can be written to the cameras memory, and represents the light information that hit the sensor, but in a way a computer can understand. • The image sensor determines the resolution and quality of the final image (by the number of light-sensitive pixels that collect information)

  23. Types of Sensors • Sensors work by having light-sensitive pixels that collect the light • This sensor technology is relatively new (within the last 30 years) and is still being improved. • Physicists are working with different materials and making different kinds of sensors that capture the light

  24. CCD Image Sensor • CCD = Charge Coupled Device • Grabs part of picture with each exposure • Array arranged in mosaic or Bayer pattern • Each pixel registers one of 3 colors • 50% green pixels are registered, 25% (each) blue and red registered • Other colors must be interpolated (guessed) • True resolution of camera is reduced because not all the light is being recorded • Array of pixels gather light and translate to a voltage • CCD sensor is just an analog device – it does not process voltage; so additional circuitry in the camera must do that • Each row read one at a time (like a conveyer belt)

  25. Foveon CMOS Image Sensor • CMOS = Complementary Metal Oxide Semiconductor • Captures RGB light at each pixel; no interpolation (3 layers of photodetectors) • Uses properties of silicon to register light absorption at different layers • No interpolation is necessary – less light is wasted • But sensor is less sensitive, so information is still lost • Pixels in sensor include the circuitry to convert voltage to the digital data • done in parallel – each pixel can be processed individually and immediately • Can record an image more quickly (theoretically) • Use less power because several functions are included on the image sensor

  26. Which image sensor is better? • Currently, CCD has better image quality and a better range • But like we said, it doesn’t do digital conversion, so it uses more power • It requires special production techniques – but generally has less noise • But, CMOS is catching up & is being used in professional level cameras because the sensors consume less power • CMOS sensors are less expensive to produce

  27. Tomorrow • Tomorrow we will look at how lenses affect what light reaches the sensor – and how that affects what image the camera sees.

  28. Lenses and Exposure Lecture 05 September 15, 2005

  29. The Lens • Lens is the eye of the camera • It captures and focuses the light onto the sensor • The lens affects the quality of the image & the kinds of pictures that you can take • What matters: • Quality of lens • Amount of light it can transmit • Focusing range • Amount of magnification

  30. Lenses: Focal Length • Focal Length: The distance from the rear nodal point of the lens to the point where the light rays passing through the lens are focused onto the image sensor • Measured in millimeters (Film standard is 35mm) • Think of it as the amount of a lens’s magnification • The longer the length, the more the lens will magnify the scene Picture from Real World Digital Photography Book

  31. Focal Length Photos from Canon Website Canon Photo Shooting- Techniques (Using a telephoto lens)

  32. Lens Aperture • Size of the opening that admits light to the sensor, relative to the magnification or focal length of the lens • f-stops (denominators of fractions indicating relative size of opening) • Each stop you open up doubles the amount of light reaching the sensor • Maximum aperture – lets in more light – good for dim lighting • Minimum aperture – how much light can you block from the sensor (used for bright lighting) • Also can increase depth-of-field f8 f4 f2

  33. Lens Speed • Lens Speed • Amount of light the lens transmits at maximum aperture • A lens with maximum aperture of f2 is “fast” compared to a lens with max aperture of f8 which is “slow” • Fast lens = large aperture - allows lens to transmit more light • Slow lens = small aperture - little light gets through

  34. Kinds of Lenses • Zoom Lens • Allows you to enlarge or reduce an image without having to get closer or farther away • Optical Zoom - changes the effective focal length of the lens • Telephoto lens • Compresses the apparent distance between objects, making them appear to be closer together • Wide-angle lens • Expands apparent distance between objects, giving vast areas of foreground, making distant objects appear to be farther away

  35. Wide vs. Telephoto Lenses Photos from Canon Website Canon Photo Shooting- Techniques photo with a wide-angle lens (35 mm) a photo with a telephoto lens (equivalent to 150 mm)

  36. Wide-angle lens • Wide angle lenses let you shoot over a wide range (vertically) • But it makes things in the background appear even further away (large depth-of-field) • It can cause strong distortions in up-close photos of subjects Photos from Canon Website Canon Photo Shooting- Techniques

  37. Telephoto Lens • Lets far away objects appear closer • Makes background objects appear to be close to subjects • Can be used to artistically blur the background (short depth of field) Photos from Canon Website Canon Photo Shooting- Techniques

  38. Shutter Speed • Is measured in seconds or fractions of a second • The duration of time the shutter opens and closes during an exposure process • How long the light flows through the lens and onto the image sensor

  39. Introduction to Exposure • Exposure is the amount of light striking the sensor • Three factors determine correct exposure • Amount of light in scene that strikes the image sensor • Length of time the sensor is exposed to light • Sensitivity of the sensor • Think of each pixel on the sensor as a little bucket that catches photons of light as they pass through the lens. • Bucket must fill up to a threshold point before the pixel will register it as part of the image • Raising or lowering the threshold mark will decrease or increase the sensitivity of the sensor

  40. Exposure • Aperture (f-stop) determines how many photons are admitted at once (like a funnel) • Shutter speed determines how much time the photons have to strike the sensor (like a valve controlled by a timer) • Aperture & shutter speed work together to create proper exposure • Buckets can be filled quickly with short shutter speed and large lens opening • Buckets can be filled slowly with long shutter speed and small lens opening •  Same exposure (same amount of light reaching the buckets)  RECIPROCITY – equivalent exposure values

  41. Reciprocity • Equivalent Exposures EV14

  42. Schedule • HW1 -- (For Friday, but bring on Tuesday) • Write 1/2 - 1 page (single-spaced) OR make a PowerPoint presentation of a mini biography of a famous photographer (not Ansel Adams), plus download or bring in 2-3 pictures taken by that photographer to show the class on Tuesdat • Tomorrow no coordinate classes this period. • HW2 - • Friday during class we will take pictures as part of Homework 2 (see website) and experiment with the lenses • Over the weekend - continue taking pictures as part of HW 2