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Colour space confusion

Before we go on to look at some real samples from the camera I'd better explain a little something I discovered about the DiMAGE 7 not long after starting this review. As I do with all my reviews I run the camera through a set of standard checks before commencing the review. These are really designed to ensure that the camera delivered isn't damaged and isn't so pre-production that it's unsuitable for review. I include a couple of colour patch shots and flowers to check colour.

Looking over the D7's images I couldn't help but feel that certain colours seemed under-saturated (mostly greens and blues). At this stage though I simply put this down to how Minolta were processing the image.

I also installed the supplied Minolta Image Viewer application (which I'll cover in more detail later in this review). I noted an interesting option when using this application, there was a 'colour matching' checkbox and you could select any one of nine industry standard colour spaces, I selected sRGB.

Testing the Image Viewer I noticed that the very same images which I'd been viewing in Photoshop and ACDSEE looked significantly different. Notably colours were far more vivid and accurate. Loading a D7 native JPEG into the Minolta Image Viewer application and re-saving it without any modifications resulted in clearly different images:

Native DiMAGE 7 image
(721 KB)
Converted by Image Viewer to sRGB
(637 KB)

For the curious among you click here for the same image saved in Adobe RGB colour space.

You can clearly see the stronger yellow, green and blues as well as a slightly different contrast (gamma). At this stage it was clear to me that the DiMAGE 7 was shooting in its own colour space and that the Minolta Image Viewer application is capable of converting this colour space into an industry accepted colour space (including sRGB, Adobe RGB and ColorMatchRGB). Indeed hunting around in the installation directory for the Image Viewer I found two ICC profiles (one for JPEG/TIFF and one for RAW), however these didn't appear to work well in Photoshop.

Thanks to Mike Chaney for producing the following CIE chromaticity charts for sRGB, Adobe RGB and the DiMAGE 7 colour spaces (both JPEG/TIFF and RAW).

sRGB color space Adobe RGB color space
(used by most professionals)
DiMAGE 7 JPEG/TIFF colour space DiMAGE 7 RAW colour space

This raises a few important points:

  • It's a good thing that the DiMAGE 7 shoots in a wider colour gamut than sRGB (which has a very limiting and tight colour gamut), however it would be better to have a menu option which allows you to select between this special proprietary wide gamut colour space and sRGB.
     
  • This is not documented in the DiMAGE 7 manual. I feel it should be made very clear to users, there's certainly a chance that the average user will simply load images directly from the camera using a card reader and never use the Minolta Image Viewer. These users may well end up disappointed by the D7's colour.
     
  • The average user won't know what colour space they're in, indeed most users don't even calibrated their monitors. However, at a consumer level, most of you will be viewing this web page and all the digital photographs you ever deal with in the sRGB colour space.
     
  • DiMAGE 7 owners will now have to use the Minolta Image Viewer to re-save their images before using them for the web, monitor viewing or printing. This adds another step into an owners workflow.

Raising this issue with Minolta they got back to me with the following statement:

The DiMAGE 7 indeed shoots in its own Colourspace in RAW mode and Tiff/JPEG compressed form.

The Minolta Colourspace is unique to 7 and 5, it most closely resembles the Colourspace of sRGB.

The Minolta Colourspace includes detail taken from the CxProcess. When a file is opened by the Minolta Utility it offers the option of conversion to another 'standard' Colourspace, or ICC profile. This translation is carried out by the Minolta software and is then offered to be retained upon saving in JPEG. Tiff files save this as a matter of course.

When you open the image directly into Photoshop or any other software other than the Minolta Utility it is unable to decipher the additional information, so it plays no part in the final image. This can lead the image to appear less vivid.

It would appear then that it is preferable to always open the images directly into the Minolta Utility first. This is possible directly from the camera or via a cardreader or similar.

I hope Minolta decide to include an addendum in the camera packaging to make owners aware of the advantages of running the images through the Image Viewer.

More examples

A few more examples of the different between images straight from the camera and those re-saved by Minolta Image Viewer:

Native DiMAGE 7 image
(1,715 KB)
Converted by Image Viewer to sRGB
(1,524 KB)
Or as Adobe RGB (1,557 KB)
Native DiMAGE 7 image
(1,886 KB)
Converted by Image Viewer to sRGB
(1,677 KB)
Or as Adobe RGB (1,572 KB)

Important review notes

From this point onwards in the review if you see the following text: "Image re-saved to sRGB colour space" you will know that the images / crops of images you are viewing have been run through the Minolta Image Viewer application. Note that NO adjustments other than the colour space conversion are made. I noticed no difference in detail (resolution) between the native and converted images. The Minolta Image Viewer appears to maintain EXIF information.


JPEG/TIFF Image Size & Quality


Standard Test Scene

The DiMAGE 7 offers a wide variety of resolution and image format options. You can choose from JPEG (three compression levels) or TIFF at 2560 x 1920 (full native resolution), 1600 x 1200, 1280 x 960 or 640 x 480. As well as RAW format which is fixed at 2560 x 1920.

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:

  • 2560 x 1920 RAW
  • 2560 x 1920 TIFF
  • 2560 x 1920 JPEG FINE
  • 2560 x 1920 JPEG STANDARD
  • 2560 x 1920 JPEG ECONOMY
  • 1600 x 1200 JPEG FINE
  • 1280 x 960 JPEG FINE
  • 640 x 480 JPEG FINE

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


 
2560 x 1920
RAW
Minolta RAW (.MRW - not available for download) as saved JPEG 2,753 KB
TIFF
14,457 KB (Not available for download)
JPEG
FINE

2,419 KB
JPEG
STD.

1,247 KB
JPEG
ECON.

827 KB
 

 
1600 x 1200
JPEG
FINE

1,040 KB
 

 
1280 x 960
JPEG
FINE

714 KB
 

 
640 x 480
JPEG
FINE

266 KB

Note that because we're looking here at the quality of the D7's JPEG/TIFF encoder none of these images have been run through the Minolta Image Viewer except for the RAW file (which must be to be viewed / converted). Overall JPEG FINE is indistinguishable from TIFF, though the RAW image looks different (though not necessarily better). After this at the STANDARD and ECONOMY settings JPEG artifacts start to become visible. The D7 delivers very nice crisp clean 1600 x 1200, 1280 x 960 and 640 x 480 images.

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