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Image Size / File Quality Options

The *ist D provides a wide variety different image size / quality combinations. Image size choices are by default 3008 x 2008 (Large), 2400 x 1600 (Middle) and 1536 x 1024 (Small). In addition the Small size can be set via custom function to either 1536 x 1024, 1152 x 768 or 960 x 640. Image size choices can be combined with either TIFF (8 bit) image format or JPEG image format with three quality level indicated by a number of stars (, , ). In addition the *ist D also has a RAW image format (.PEF extension), this contains a RAW 'dump' of the data directly from the sensor (12-bits per pixel). Most people consider the RAW format to be the 'digital negative' because it is lossless and has had no image processing applied to it (tone, white balance, sharpening etc.) all of which can be adjusted at a later date before outputting the final image (Pentax include Photo Browser and Photo Laboratory for this purpose).


Standard Test Scene

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:

  • 3008 x 2008 RAW (to TIFF using Photo Laboratory 1.0)
  • 3008 x 2008 (L) TIFF
  • 3008 x 2008 (L) JPEG
  • 3008 x 2008 (L) JPEG
  • 3008 x 2008 (L) JPEG
  • 2400 x 1600 (M) JPEG
  • 1152 x 768 (S) JPEG

Crops below are of the same 240 x 100 area of each image nearest neighbour magnified 200%.

Settings: ISO 200, FA 50 mm F1.4 @ F8


 
3008 x 2008
RAW
13,608 KB .PEF (not available for download), VGA crop - 718 KB .TIF
TIFF
17,708 KB .TIF (not available for download), VGA crop - 762 KB .TIF
JPEG

2,756 KB
JPEG

1,584 KB
JPEG

1,064 KB
   

 
2400 x 1600
JPEG

1,971 KB
   

 
1536 x 1024
JPEG

1,047 KB

TIF output from a RAW converted in Pentax's Photo Laboratory and TIF output from the camera were virtually identical, although obviously RAW is more flexible and approximately 4 MB smaller (I'm not sure many people will be using the TIFF option). JPEG quality has no visible artifacts, drop down to and you can begin to see "mosquito artifacts" around areas of detail. Also interesting (although not strictly relevant here) is that both RAW and TIFF modes produce visibly sharper images than JPEG, hinting that either the camera doesn't sharpen JPEG images as much as TIFF or that the JPEG encoding algorithm itself is somehow affecting the sharpness of the image (I know no technical reason for this).

The camera's downsampling interpolation algorithm appears to be of a high quality with clean sharp images at the smaller image sizes.


Color space

The *ist D provides output color space options of sRGB and Adobe RGB. My only niggle about this is that the option is tucked away on the last page of the custom functions menu, it really should be on the main menu with the other image parameters (contrast, sharpness, saturation). Also like many other digital SLR's the *ist D does not embed the color space profile into the image file so you will have to either remember which shots were taken in which color space or use the Pentax Photo Browser to verify the color space used.

Settings: ISO 200, FA 50 mm F1.4, 1/40 sec, F7.1

sRGB Adobe RGB -> sRGB

Place your mouse over the labels below the image to see a ColorChecker chart taken in each color space. Note that the Adobe RGB image has been converted to the sRGB color space for correct color on your monitor. Below are two studio shots taken as both sRGB and Adobe RGB. Note that in these samples the Adobe RGB image has NOT been converted to sRGB and so to view it correctly you will have to load it into a color space aware photo application and assign the Adobe RGB color space. Below each sample is that image's CIE u'v' Color Distribution chart; larger gray triangle approximately represents the range of color which the human eye can resolve, the inner triangle the available gamut in each color space (sRGB or Adobe RGB).

Settings: ISO 200, FA 50 mm F1.4 @ F14 (Studio Strobe), Small/

sRGB Adobe RGB
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