This article contains my notes for the IOP courses unit 2, understanding the technology of digital photography.
- Megapixels
- A megapixel refers to the size and resolution of the pictures that a digital camera can produce.
- Light sensors are pixels.
- The term megapixel is the total number of light sensors a cameras image sensor has.
- The resolution of a digital photograph is defined by the total number of pixles it contains.
- A cameras resolution is calculated by multiplying the total number of vertical pixels by the total number of horizontal pixels.
- TOPTIP: Image quality depends on more than the image sensor:
- The quality of the lens used.
- The quality of the image processing in the camera.
- Image sensor
- There are two types:
- CCD ( Charged Coupled Device )
- CMOS ( Complementary Metal-oxide-Semiconductor )
- Within these sensor types there are different categories:
- Full frame
- APS-C
- The APS-C cropped sensor is the most widely used sensor.
- Typically this means a crop factor of 1.5 or 1.6.
- This means you will need a dedicated lens in order to get 'true' wide-angle results.
- These lenses are also less expensive than full-frame counterparts.
- Four thirds
- Made by Olympus in a bid to improve the quality of images produced by cameras sporting smaller, more compact bodies than the traditional SLRs.
- The format has been slow to catch on.
- The Four-Thirds sensor system is not based on film SLR formats and consequently an entirely new lens mount was created to support the growing range of exclusively 'digital' lenses produced to support it.
- Four thirds it the smallest sensor.
- Which means the body of the camera can be smaller as well.
- Although this type of sensor produces more noise than the others, it is not practically noticeable due to Olympus and Panasonic's image processing technology.
- Crop factor
- Used to describe how much smaller a cameras sensor is than the standard 35mm film format.
- 35mm format came from old 35mm film and it now used as a reference size in the digital age.
- APS-C are smaller which means there focal length is greater, e.g. 50mm lens with a crop factor of 1.6 would give you the equivalent field of view of a 80mm lens.
- Working with a cropped sensor is not all bad though, as when working with telephoto subjects your 300mm lens can produce an equivalent focal length of 450mm.
- Cropped sensor bodies are more affordable.
- They are also good at getting very shallow depth of field effects.
- This makes it particularly well suited for portrait work with fast f1.8 or f2 lenses.
- Unfortunately this also makes it hard for the camera to get everything in the frame in focus.
- Overall, however, working with a full frame sensor affords the photographer more control over depth of field.
- There are two types:
- Resolution
- Scaling images makes them pixelated.
- Interpolation (sometimes called resampling) is the method of increasing or decreasing the number of pixels in a digital image. some digital cameras use interpol produce a large image than the sensor captured or to create digital zoom.
- Resolution in digital photography printing is defined as pixles per inch (PPI) or DPI (dots per inch).
- Inkjet printers work best with images that have a resolution between 200 and 300ppi.
- A computer monitor is 72 DPI.
- File formats
- Every image you capture uses three colours, red, green and blue.
- To store this information, the computer uses 8 bits of data, so 3 x 8 bits = 24-bit image.
- JPEG
- Acronym stands for Joint Photographic Experts Group.
- Who are a industry body setup to agree on an image compression format that would make digital pictures more versatile and easier to use and upload on computers and the internet.
- The JPEG format allows images to be stored with logs of detail with relatively small file sizes.
- They can reduce the size image size by 20 times.
- Unfortunately there is a trade off, the algorithm uses the fact that our syustes are more tuned in to spotting variations in detail than colour. It compresses the colour information inside the image more than the details it contains.
- All cameras allow you to specify how much compression to apply (small, medium or large).
- The size dictates the image quality, so the large size is a high image quality and thus a smaller compression is applied.
- RAW
- Unlike JPEG, raw has a more literal mean, as in the raw file.
- When the shutter releases each light sensor records the colour, this the the raw format.
- This gives you more control as you can change the saturation, exposure, white balance, etc after the shot has been taken.
- The beauty of RAW is the colour depth and detail is preserved.
- What's more, many of the setting you choose for the image can be undone on the computer.
- Because RAW files contain so much more information than JPEGs( generally 12 bits verus 8 bits) subtle tonal variations in shadows and highlights are faithfully recorded, producing an image with a high dynamic range.
- RAW can only be viewed on the computer using specialist software such as Photoshop.
- The other problem with RAW is speed.
- Some cameras allow you to save both RAW and JPEGs of the image.
- Scene modes
- Auto exposure
- Shutter priority
- Aperture priority
- EV, exposure compensation can be used to control the exposure, e.g. a man in a black suit will cause the camera to over expose, use -1EV to tone things down.
- Focus modes
- Use Single area Autofocus for still subjects (AF-S)
- Continuous Autofocus for moving subjects
- Hybrid Autofocus (AF-A) can do both, downside of AF-A is it does not work well with fast moving objects.
- White balance
- Cameras, unlike our eyes struggle with changes in colour temperate.
- Most cameras have auto white balance to over comethis
- White balance can be changed
- Photo means light in Greek and graphis means to paint, so photograph translates to Painting with light.
- Shutter speeds
- Freezing motion
- by using a fast shutter speed like 1.2,000 sec will stop a moving object in its tracks.
- Suggest motion
- by using a slow shutter speed like 1/80th sec will create a blur effect.
- Panning action
- Same as above but move the camera along with the moving object to create a slightly blured effect around the object, giving the impression of speed.
- Action Scene Modes
- This is a camera mode that will automatically freezes the action without you having to manually select a shutter speed.
- Use shutter speed and depth of field
- using a low fstop like f2.8 creates a shall depth of field with will blur the background whilst keeping the subject in focus (bokeh)
- Long exposures and traffic trails
- Use long exposure for night time photograph, this allows more light to hit the image sensor.
- Long exposures can also be used for waterfalls or traffic merging a lot of light into one photograph.
- TOPTIP: Use a high ISO setting when shooting at nighttime if you don't have a tripod and cant lower the shutter speed, however high ISO settings can can distortion on the image.
- Freezing motion