Resolution, Bit Depth, and Color Printing Knowledge
Resolution, Bit Depth, and Color

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.


Resolution
 
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 the image.
  • 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.

 

Resolution Selection
 
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 materials
  • 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 quality output.
 

  • 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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