Whertha's Favorite Links on camera from Diigo

ConsumerReports.org - Digital cameras: How to choose

Wed, 09 Aug 2006 13:27:48 -0000

Highlights and Sticky Notes:

Professional digital cameras use as many as 14 megapixels.

If you mainly want to make 4x6 snapshots, a camera with a 3- or 4-megapixel resolution will be fine

But to enlarge the image more or enlarge only part of it, you'll want a 6- to 8-megapixel camera.

Two of the more important capabilities are a zoom range of 5x to 10x or more,

a full complement of manual controls that you determine the shutter speed and lens opening

We think it's more convenient to own a camera that accepts AA batteries.

Most models let you shoot an image every few seconds, but a few make you wait 5 seconds or more

Tags: camera

Posted by: whertha

Burst (Continuous): Camera System: Glossary: Learn: Digital Photography Review

Wed, 09 Aug 2006 13:27:31 -0000

Highlights and Sticky Notes:

Burst or Continuous Shooting mode is the digital camera's ability to take several shots immediately one after another, similar to a film SLR camera with a motorwind.

Tags: camera

Posted by: whertha

Buffer: Camera System: Glossary: Learn: Digital Photography Review

Wed, 09 Aug 2006 13:27:31 -0000

Highlights and Sticky Notes:

After the sensor is exposed, the image data will be processed in the camera and then written to the storage card. A buffer inside a digital camera consists of RAM memory which temporarily holds the image information before it is written out to storage card. This speeds up the "time between shots" and allows burst (continuous) shooting mode. The very first digital cameras didn't have any buffer, so after you took the shot you HAD to wait for the image to be written to the storage card before you could take the next shot.

Tags: camera

Posted by: whertha

AF Servo: Camera System: Glossary: Learn: Digital Photography Review

Wed, 09 Aug 2006 13:27:31 -0000

Highlights and Sticky Notes:

Autofocus Servo refers to the camera's ability to continuously focus on a moving subject, a feature normally only found on digital SLRs. It is generally used by sports or wildlife photographers to keep a moving subject in focus.

Tags: camera

Posted by: whertha

AF Assist Lamp: Camera System: Glossary: Learn: Digital Photography Review

Wed, 09 Aug 2006 13:27:31 -0000

Highlights and Sticky Notes:

Some manufacturers fit their cameras with a lamp (normally located beside or above the lens barrel) which illuminates the subject you are focusing on when shooting in low light conditions. This lamp assists the camera's focusing system where other cameras autofocus will likely have failed. These lamps usually only work over a relatively short range, up to about 4 meters. Some lamps use infrared light instead of visible light which is better for "candid" shots where you don't want to startle the subject.

Tags: camera

Posted by: whertha

Dynamic Range: Digital Imaging: Glossary: Learn: Digital Photography Review

Wed, 09 Aug 2006 13:27:31 -0000

Highlights and Sticky Notes:

The dynamic range of a sensor is defined by the largest possible signal divided by the smallest possible signal it can generate. The largest possible signal is directly proportional to the full well capacity of the pixel. The lowest signal is the noise level when the sensor is not exposed to any light, also called the "noise floor".

Practically, cameras with a large dynamic range are able to capture shadow detail and highlight detail at the same time

Tags: camera

Posted by: whertha

AD Converter: Camera System: Glossary: Learn: Digital Photography Review

Wed, 09 Aug 2006 13:27:31 -0000

Highlights and Sticky Notes:

Most consumer digital cameras use 8 bit ADCs, allowing up to 256 (2^8) distinct values for the brightness of a single pixel.

The minimum bit rate (resolution) of an ADC is determined by the dynamic range (accuracy) of the sensor. If the dynamic range of the sensor is for instance 1000:1 (also quoted as 60dB) the ADC should be at least 10 bit (2^10 = 1,024 discrete levels) in order to avoid loss of information.

Tags: camera

Posted by: whertha

Pixels: Camera System: Glossary: Learn: Digital Photography Review

Wed, 09 Aug 2006 13:27:30 -0000

Highlights and Sticky Notes:

Similar to an array of buckets collecting rain water, digital sensors consist of an array of "pixels" collecting photons, the minute energy packets of which light consists. The number of photons collected in each pixel is converted into an electrical charge by the light sensitive photodiode. This charge is then converted into a voltage, amplified, and converted to a digital value via the analog to digital converter, so that the camera can process the values into the final digital image.

As explained in the sensor sizes topic, sensors of digital compact cameras are substantially smaller than those of digital SLRs with a similar pixel count. As a consequence, the pixel size is substantially smaller. This explains the lower image quality of digital compact cameras, especially in terms of noise and dynamic range.

Tags: camera

Posted by: whertha

EXIF: Camera System: Glossary: Learn: Digital Photography Review

Wed, 09 Aug 2006 13:27:30 -0000

Highlights and Sticky Notes:

Besides information about the pixels of the image, most cameras store additional information such as the date and time the image was taken, aperture, shutterspeed, ISO, and most other camera settings. These data, also known as "metadata" are stored in a "header". A common type of header is the EXIF (Exchangeable Image File) header. EXIF is a standard for storing information created by JEIDA (Japan Electronic Industry Development Association) to encourage interoperability between imaging devices. EXIF data are very useful because you do not need to worry about remembering the settings you used when taking the image. Later you can then analyze on your computer which camera settings created the best results, so you can learn from your experience

Tags: camera

Posted by: whertha

Effective Pixels: Camera System: Glossary: Learn: Digital Photography Review

Wed, 09 Aug 2006 13:27:30 -0000

Highlights and Sticky Notes:

A distinction should be made between the number of pixels in a digital image and the number of sensor pixel measurements that were used to produce that image. In conventional sensors, each pixel has one photodiode which corresponds with one pixel in the image. A conventional sensor in for instance a 5 megapixel camera which outputs 2,560 x 1,920 images has an equal number of "effective" pixels, 4.9 million to be precise.

Tags: camera

Posted by: whertha

Color Filter Array: Camera System: Glossary: Learn: Digital Photography Review

Wed, 09 Aug 2006 13:27:30 -0000

Highlights and Sticky Notes:

Each "pixel" on a digital camera sensor contains a light sensitive photo diode which measures the brightness of light. Because photodiodes are monochrome devices, they are unable to tell the difference between different wavelengths of light. Therefore, a "mosaic" pattern of color filters, a color filter array (CFA), is positioned on top of the sensor to filter out the red, green, and blue components of light falling onto it. The GRGB Bayer Pattern shown in this diagram is the most common CFA used.

The missing pixels in each color layer are estimated based on the values of the neighboring pixels and other color channels via the demosaicing algorithms in the camera.

Tags: camera

Posted by: whertha

White Balance: Digital Imaging: Glossary: Learn: Digital Photography Review

Wed, 09 Aug 2006 13:27:29 -0000

Highlights and Sticky Notes:

Most digital cameras feature automatic white balance whereby the camera looks at the overall color of the image and calculates the best-fit white balance. However these systems are often fooled especially if the scene is dominated by one color, say green, or if there is no natural white present in the scene

Most digital cameras also allow you to choose a white balance manually, typically sunlight, cloudy, fluorescent, incandescent etc. Prosumer and SLR digital cameras allow you to define your own white balance reference. Before making the actual shot, you can focus at an area in the scene which should be white or neutral gray, or at a white or gray target card. The camera will then use this reference when making the actual shot.

Tags: camera

Posted by: whertha

Firmware: Camera System: Glossary: Learn: Digital Photography Review

Wed, 09 Aug 2006 13:27:29 -0000

Highlights and Sticky Notes:

A digital camera's sensor, buffer, LCD, autofocus, etc. are controlled by a set of microprocessors which in turn are controlled by "firmware", which is software stored in the Read Only Memory (1) of the camera. Many cameras allow the firmware to be upgraded (2) in order to enhance performance and/or add new features. This is done by downloading an installer from the camera manufacturer's website, followed by running it from a computer connected to the camera via a USB cable, or by running the installer from the memory card inside the camera.

Tags: camera

Posted by: whertha

Sensor Linearity: Camera System: Glossary: Learn: Digital Photography Review

Wed, 09 Aug 2006 13:27:29 -0000

Highlights and Sticky Notes:

Sensors are linear devices. If you double the amount of light, the sensor output will double, as long as the pixels are not full (*). Once a pixel reaches full capacity, it will give a constant or "clipped" output. Human vision is non-linear, as explained in the dynamic range topic. A doubling of the light in low light conditions has a much larger effect than in bright conditions. Our vision amplifies the shadows and compresses the highlights.

digital cameras apply a tonal curve to the linear raw data so that images viewed on a monitor or printed images are more pleasing to the eye. Applying a gamma correction of 1/2.2=0.45 will allocate more tones to the shadow areas and fewer tones to the highlight areas in line with the characteristics of our vision. When working in a gamma 2.2 color space like sRGB or Adobe RGB the images will appear perceptually uniform on a monitor or print, avoiding posterization (banding).

Tags: camera

Posted by: whertha

Sensor Sizes: Camera System: Glossary: Learn: Digital Photography Review

Wed, 09 Aug 2006 13:27:29 -0000

Highlights and Sticky Notes:

This diagram shows the typical sensor sizes compared to 35mm film. The sensor sizes of digital SLRs are typically 40% to 100% of the surface of 35mm film. Digital compact cameras have substantially smaller sensors offering a similar number of pixels. As a consequence, the pixels are much smaller, which is a key reason for the image quality difference, especially in terms of noise and dynamic range.

Tags: camera

Posted by: whertha

Pixel Quality: Camera System: Glossary: Learn: Digital Photography Review

Wed, 09 Aug 2006 13:27:29 -0000

Highlights and Sticky Notes:

The marketing race for "more megapixels" would like us to believe that "more is better". Unfortunately, it's not that simple. The number of pixels is only one of many factors affecting image quality and more pixels is not always better. The quality of a pixel value can be described in terms of geometrical accuracy, color accuracy, dynamic range, noise, and artifacts. The quality of a pixel value depends on the number of photodetectors that were used to determine it, the quality of the lens and sensor combination, the size of the photodiode(s), the quality of the camera components, the level of sophistication of the in-camera imaging processing software, the image file format used to store it, etc.

Conventional sensors using a color filter array have only one photodiode per pixel location and will display some color inaccuracies around the edges because the missing pixels in each color channel are estimated based on demosaicing algorithms. Increasing the number of pixel locations on the sensor will reduce the visibility of these artifacts. Foveon sensors have three photodetectors per pixel location and create therefore a higher color accuracy by eliminating the demosaicing artifacts. Unfortunately their sensitivities are currently lower than conventional sensors and the technology is only available in a few cameras.

Dynamic Range

The size of the pixel location and the fill factor determine the size of the photodiode and this has a big impact on the dynamic range. Higher quality sensors are more accurate and will be able to output a larger dynamic range which can be preserved when storing the pixel values into a RAW image file. A variant of the Fujifilm Super CCD, the Super CCD SR uses two photodiodes per pixel location with the objective to increase the dynamic range. A more sensitive photodiode measures the shadows, while a less sensitive photodiode measures the highlights.

Tags: camera

Posted by: whertha

Sensitivity (ISO): Digital Imaging: Glossary: Learn: Digital Photography Review

Wed, 09 Aug 2006 13:27:29 -0000

Highlights and Sticky Notes:

digital cameras have an ISO rating indicating their level of sensitivity to light. ISO 100 is the "normal" setting for most cameras, although some go as low as ISO 50. The sensitivities can be increased to 200, 400, 800, or even 3,200 on high-end digital SLRs. When increasing the sensitivity, the output of the sensor is amplified, so less light is needed. Unfortunately that also amplifies the undesired noise. Incidentally, this creates more grainy pictures, just like in conventional photography, but because of different reasons.

Tags: camera

Posted by: whertha

Barrel Distortion: Optical: Glossary: Learn: Digital Photography Review

Wed, 09 Aug 2006 13:27:28 -0000

Highlights and Sticky Notes:

Barrel distortion is a lens effect which causes images to be spherised or "inflated".

Tags: camera

Posted by: whertha

Anti-shake: Optical: Glossary: Learn: Digital Photography Review

Wed, 09 Aug 2006 13:27:28 -0000

Highlights and Sticky Notes:

Another approach to image stabilization is to make the CCD move so that it compensates for the camera movement as implemented in the Konica Minolta DiMAGE A2. The sensor is mounted onto a platform which moves in the opposite way as the movement of the camera, which is determined by motion detectors. According to Konica Minolta, this "anti-shake" system gives you an additional 3 stops. For example if you would require a shutterspeed of 1/1000s to shoot a particular scene, you should be able to shoot at only 1/125s (8 times slower) with anti-shake enabled.

Tags: camera

Posted by: whertha

Image Stabilization: Optical: Glossary: Learn: Digital Photography Review

Wed, 09 Aug 2006 13:27:28 -0000

Highlights and Sticky Notes:

mage stabilization helps to steady the image projected back into the camera by the use of a "floating" optical element—often connected to a fast spinning gyroscope—which helps to compensate for high frequency vibration (hand shake for example) at these long focal lengths.

Tags: camera

Posted by: whertha