08.12.2012 Views

Imatest Documentation

Imatest Documentation

Imatest Documentation

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

<strong>Imatest</strong> <strong>Documentation</strong><br />

but their noise may be objectionable at high ISO speeds. Dpreview.com has found the Sony DSC-828's noise at ISO 64 to be as<br />

high as the Canon EOS-300D (similar to the EOS-10D) at ISO 800.<br />

The 6 megapixel raw/12 megapixel interpolated Fuji S7000, which uses Fuji's SuperCCD, has sharpness comparable to the Sony<br />

F828. It also has some problems with noise. The SuperCCD is based on an interesting concept. Thanks to gravity, most detail in<br />

nature is vertical or horizontal, and evolution has made our eyes are more sensitive to those directions. SuperCCD pixels are located<br />

on a diagonal grid where the spacing between x and y-pixel spacings is 1/sqrt(2) = 0.707 that of a normal grid the same number of<br />

pixels. The diagonal grid is interpolated to a horizontal grid that has twice the pixels, keeping the reduced pixel spacing. This results<br />

in an impressive gain in horizontal and vertical resolution, though sharpness is slightly below that of a sensor with the same number<br />

of uninterpolated pixels.<br />

I analyzed the sides of Fuji F7000 because dpreview.com noted a problem with softness on the left side. Uncorrected<br />

MTF50 is the appropriate metric for comparing portions of a single image. The problem is indeed very evident. It seems to be<br />

slightly worse on the left, where MTF50 (uncorrected) is 62% of the center value. The lens alsohas a problem with chromatic<br />

aberration. The Sony DSC-F828 does much better: edge MTF is 93% of the center value. It apears to have a finer lens, at least at<br />

the focal length and aperture chosen for the test.<br />

The Sigma SD9 has high resolution for its pixel count because it doesn't have, and probably doesn't need, an anti-aliasing filter. If<br />

only Foveon could break the 3.4 megapixel barrier...<br />

Links<br />

Scanner Bake-off 2004 Jim Hutchinson used <strong>Imatest</strong> results in his comparison of scanners.<br />

35 of 451

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!