RAW
The sensor in most digital cameras has a 12 bit resolution, this
means in simple terms that each pixel can have value from 0 to 4098 to
represent its brightness value. JPEG files, used for saving images only
have a resolution of 8 bits, so the values have to be scaled down.
Furthermore the sensor response is not usually linear, so corrections
have to be applied, and corrections made for ambient light (white balance).
The sensor only records luminosity, not colour. Colour is obtained by a
trick using a filter in front of the sensor. Another trick is applied
which defocuses the image to improve rendering, hence the need for sharpening.
All these adjustments and corrections are applied to the image when the camera
saves a JPEG file. However most high end cameras can also store the raw
image as recorded by the sensor, and this is called a RAW file. Because
the RAW image is uncorrected it will normally look worse than the JPEG version,
however it can be processed by software to apply corrections and these are under
your control rather just a default set of changes; your adjustments are normally
done with sliders so you can adjust until it is what you want.
Each manufacturer usually has their own file extension that they use
for saving the RAW file; cr2, nef, kdc, orf, etc.. Adobe also
defined a RAW format with the extension dng which stands for Digital
NeGative, which they submitted to ISO to be issued as a
standard. Most software can handle DNG files. Adobe supply a
utility to convert RAW files to the DNG format, see
Mike Fuller's note. The
wikipedia article
on RAW files contains a list of file extensions and other useful information.
If you are going to get serious about photography then it is
recommended to shoot in RAW + JPG. The JPEG gives you the cameras best
attempt at conversion and can be reviewed on the camera in the field, and also
provides a windows thumbnail for File Explorer. The RAW file is for you
to post process and create the best image you can, even if this is a few years
later when you have mastered Photoshop.
Red-Eye
Usually found on cameras as a setting called "Red Eye Reduction".
"Red eye" is an effect that occurs when using flash, if the subject is looking
directly at the camera, then the flash can light up the retina at the back of the
eye which can be seen through the subject's pupils. This effect can be
corrected in post production by making little selection circles over the
effected part and reducing the red component. Some cameras can do this
automatically for you.
Resolution
This is a measure of the detail in an image, the higher the
resolution the more detail there is in the image. Resolution is related
to viewing distance and is another of those subjects which gets complicated as
soon as the mathematicians start, see
wikipedia
if you don't believe me. However there is a simpler explanation in the
first topic.
An important point, so I will repeat it, is that you can not see the
full resolution of your image on your computer (unless you have a screen that
displays 12 megapixels or so) and certainly not on the screen on the back of
the camera. You can see a small part of your image at full resolution by
using actual pixels.
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