SUMMARY
Digital images are broken into a chessboard pattern of pixels.
The more pixels the camera (or scanner) can record, the more detail
the image will retain. Image data are recorded by storing the levels
of red, green, and blue (i.e. RGB) light striking each pixel as a
numerical value of 0-255.
Cameras are defined by the number of pixels recorded by the
CCD image sensor (e.g., a 1.6 megapixel camera will have a 1600 x 1000
pixel sensor). Most cameras allow recording at resolutions (pixel
dimensions) other than that of the CCD array, but in general the best
results will be obtained by recording the image at the default CCD
array size.
Image data can be stored in its uncompressed state of 24 bits / 3
bytes per pixel as a TIFF file, or processed in the camera using JPEG
compression. TIFF provides the highest resolution images, but minimal amounts of
in-camera JPEG compression can yield significant space savings with very little
loss of image detail. It is very difficult to tell the difference between TIFF
and low-compression JPEG recording by the time the images is edited, resized,
sharpened, and output on an ink jet or other printer. Excessive amounts of
in-camera JPEG compression should be avoided because image detail is forever
lost.
Most cameras apply some degree of processing to the images
to increase the apparent sharpness. Excessive sharpening results in a
visible "halo" around dark objects. Because the amount of
sharpening needed varies with output mode the sharpening is best done
during the post-processing phase using an image editing application
such as Adobe PhotoShop. In light of this, a camera which allows the
user to control sharpness is very desirable. Other factors such as the
camera optics and design can affect the overall quality of the image.
With my Kodak DC290 I use the low-compression JPEG mode at the maximum
CCD resolution size of 1200 x 1792 pixels for most photos. In this mode I am
able to fit about 92 images on a 64MB Compact Flash card. The actual number
varies because JPEG file sizes vary. For example an image with a flat background
with large areas of similar tone may have a file size of 250K, but one with a
large range of tones and fine detail may be 850K. A 1200 x 1792 TIFF file is
always 6.6 MB regardless of image content. Since I edit all of my images in
Adobe PhotoShop I use no in-camera sharpening. The DC290 uses the Flashpoint
Digita operating system, which allowed me to write a script for the camera which
turns off the default sharpening.
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