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JPEG Image Size & Quality


Standard Test Scene

The Optio 550 allows you to select image size and quality separately. For image size you have the following options; 2592 x 1944, 2048 x 1536, 1600 x 1200, 1024 x 768 and 640 x 480. For image quality there are three levels of JPEG compression represented by one, two or three stars (best) plus a TIFF uncompressed option. It's interesting that Pentax has chosen to use a larger-than-the-rest (other 5 mp digital cameras) 2592 x 1944 image size, this pushes the output pixel count to just greater than 5 million (the rest are 4.92 million).

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:

  • 2592 x 1944 TIFF
  • 2592 x 1944 JPEG
  • 2592 x 1944 JPEG
  • 2592 x 1944 JPEG
  • 1600 x 1200 JPEG
  • 1600 x 1200 JPEG
  • 1024 x 768 JPEG

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


 
2592 x 1944
TIFF
14,873 KB - not available for download

2,803 KB

1,174 KB

759 KB
 

 
2048 x 1536

1,113 KB
 

 
1600 x 1200

695 KB
 

 
1024 x 768

360 KB

As we normally find highest quality JPEG (three star in the case of the Optio 550) is virtually indistinguishable from the TIFF image. However a three star full resolution image weighs in at 2.7 MB, not a small file by anyone's standards. Most people will opt for the two star quality where there are some very slight artifacts around detail edges, but nothing that would be particularly noticeable at reasonable viewing or print sizes. The Optio 550 appears not to apply any interpolation to downsampled images, hence the jagged appearance of reduced resolution images (such as the 1024 x 768 above).


Image parameters

The Optio 550 allows you to modify the contrast, saturation or sharpness levels which are applied to the image before it is converted to its output format. It provides just three levels of adjustment for each parameter (-1,0,+1) which is a surprise because I would have expected more latitude on a prosumer digital.

Image parameters: Contrast

  Contrast Luminosity histogram
-1
0
+1

Image parameters: Saturation

  Saturation 100% crop
-1
0
+1

Image parameters: Sharpness

  Sharpness, 100% crop
-1
0
+1
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