The maximum resolution (in pixels) and color bit depth are
the key factors that determine the quality of the image from the digital camera.
Resolution defines how many pixels a CCD image sensor can capture when taking
a picture, while bit depth defines the number of color bits per pixel. The higher
the resolution, the better the image, but storing high-resolution images reduces
the number of images that can be placed into the camera's memory bank. Similarly,
the higher the bit depth, the richer the color.
With higher resolutions, an image will have much sharper definition
to the edge of all subjects in the image. It can be enlarged in size
and/or output to print and still retain the sharpness of detail. Images
with lower resolution cannot be effectively enlarged without losing
quality. The pixels become "blocky" and very visible with
rough or jagged edges around the subject matter.
Resolution can be expressed as either optical or interpolated.
- Optical resolution is a more reliable gauge for the quality of
- Optical resolution is determined by the number of pixels a camera
can capture both horizontally and vertically such as 1280 x 960.
- Interpolated resolution inspects two pixels, averages the data
pertaining to them, and then applies an algorithm to create a third
pixel placed between the other two. Thus, the interpolated resolution
will always be higher than the optical.
- When choosing a camera, optical or true resolution is more important
to consider than interpolated resolution. Interpolated is often
the resolution stated by camera manufacturers as the resolution
of the camera.
Selection of resolution for the stored or output images will depend
on the end use of the images. A resolution calculation would be as
follows: 640 x 480 = 307,200 total pixels or 640 distinct dots
on each of 480 horizontal lines.
Low resolution: 640 x 480
- Use: Web sites and multimedia presentations
- Average camera media storage: 30 or more images
Medium resolution: 1024 x 768
- Use: Proofs, inspection work, mock-ups, and general purpose
- Average camera media storage: 10 to 25 images
High resolution: 1280 x 960, 1524 x 1012,
1768 x 1152, 1792 x 1200
- Use: Higher quality print output for magazines, folders, or promotional
- Average camera media storage: 5 to 10 images
Examples of Resolution Setting for Image Output
1. Web output: 320 x 240 pixel resolution for lower quality
2. Web output: 640 x 480 pixel resolution for higher quality
3. Print output: A minimum of 1600 x 1200 pixel resolution
- Provides 4" x 6" image with 266 dpi
- Provides 8" x 6" image with 200 dpi
- As a comparison, 1800 x 1200 delivers a 4" x 6" image
at 300 dpi
As a general rule, the following resolutions can apply for print output.
The resolutions do not take into consideration any cropping of the
image, which may require going to a higher resolution for a higher
- 1000 x 700 pixels for 5" x 7" prints - medium quality
- 1280 x 960 pixels for 5" x 7" prints - high quality
- 1280 x 960 pixels for 8" x 10" prints - medium quality
- 1600 x 1200 pixels for 8" x 10" prints - high quality
- 1600 x 1200 pixels for 11" X 14" prints - medium quality
- 1920 x 1600 pixels for 11" x 14" prints - high quality
Color and Bit Depth
Color depth or bit
depth is the term applied to the ability of the camera sensor
to record the spectrum of colors in the image. Digital images are
recorded as pixels, which are small square blocks or picture elements
that are combined to form the image. Pixels are created as tiny points
of light, which have been converted from data compiled by the camera's
image sensor. Each pixel contains information about the colors recorded.
The color depth refers to the number of bits within each pixel and
the corresponding number of colors within those bits. When more data
can be recorded or captured (higher resolution devices), the bit depth
is higher, which results in greater color accuracy. If, for example,
24 bits of color are recorded, each image pixel will have 8 bits of
data for each of the three color channels of red, green and blue.
The higher the bits, the better the color reproduction, and consequently,
the larger the overall file size. Almost all consumer and professional
digital cameras capture images in 24-bit color, however, the studio
digital camera backs (the high performance sensor and storage attachments
for digital camera bodies) capture images in 30 or 42 bits.
To insure better color images and increased color
accuracy, it is important to select camera models offering RGB color
filtering. Other factors controlling color quality include the quality
of the optics, the circuitry controlling the camera color imaging,
and the program algorithms used in the camera's computer chip to control
the analog to digital conversion of data.
The blown-up section in the illustration at the
left shows a close-up view of the pixels from the corresponding area
of the bitmap image.
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