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JPEG Quality / Image Sizes


Standard Test Scene

The Coolpix 775 offers nine combinations of image size and quality. There are three image size options: 1600 x 1200 (FULL - CCD native resolution), 1024 x 768 (XGA), 640 x 480 (VGA). In combination with any of these you can select one of the three image quality options: FINE (JPEG 4:1), NORMAL (JPEG 8:1), BASIC (JPEG 16:1). Note: the 775 doesn't have a TIFF option.

To give an impression of what some of the combinations of image size and quality produce the table below is a cross reference of some of them:

  • 1600 x 1200 Fine
  • 1600 x 1200 Normal
  • 1600 x 1200 Basic
  • 1024 x 768 Fine
  • 640 x 480 Fine

Images below are cropped 240 x 100 area of the image magnified 200% (nearest neighbour).


 
1600 x 1200
Fine
590 KB
Normal
389 KB
Basic
226 KB
 

 
1024 x 768
Fine
291 KB
 

 
640 x 480
Fine
132 KB

Looking at the 1600 x 1200 images JPEG artifacts only really become a problem at the Basic compression setting, above this Normal does a very good job of maintaining detail and colour without introducing any major artifacts. Clearly if you're shooting for the best quality you'll use the Fine setting, but for every day shots Normal should suffice (and offer a good number of frames per storage MB).


Digital Zoom

Digital Zoom is implemented by cropping a center portion of the image captured by the CCD. Depending on the output image size this will then be either reduced (downsampled), used as is or enlarged (interpolated). Digital Zoom can be useful when using lower output resolutions than that of the CCD. The Coolpix 775 offers digital zoom's of 1.25x, 1.6x, 2.0x and 2.5x. For example, using digital zoom at XGA (1024 x 768) resolution would perform the following:

  • XGA 1024 x 768, no digital zoom - 1600 x 1200 image is reduced to 1024 x 768
  • XGA 1024 x 768, 1.25x digital zoom - 1280 x 960 crop is reduced to 1024 x 768
  • XGA 1024 x 768, 1.6x digital zoom - 1024 x 768 crop
  • XGA 1024 x 768, 2.0x digital zoom - 800 x 600 crop is enlarged to 1024 x 768 *
  • XGA 1024 x 768, 2.5x digital zoom - 640 x 480 crop is enlarged to 1024 x 768 *

* No additional image detail is gained by using digital zoom

We can see the results of different digital zoom settings at XGA resolution in the 100% crops below:

3x optical zoom, No digital 3x optical zoom, 1.25x digital zoom
3x optical zoom, 1.6x digital zoom 3x optical zoom, 2.0x digital zoom
 
3x optical zoom, 2.5x digital zoom  

Here you can clearly see that the 2.0x and 2.5x digital zoom's are simply enlarging (using nearest neighbour interpolation) the same crop used for the 1.6x digital zoom image.

Thus, using digital zoom at 1600 x 1200 resolution gains nothing, using digital zoom at 1024 x 768 gains image detail up to 1.6x digital zoom, using digital zoom at 640 x 480 will gain image detail at any digital zoom value.
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