Digital BW, The Print

----- Original Message -----
From: "Anthony Atkielski" <atkielski@...>


> Bob writes:
>
> > Surely every pixel on a digital camera (except
> > for a few exotica) is interpolated?
>
> No.  Normally each pixel in the output image corresponds to a physical
pixel
> in the CCD.  The only interpolation that occurs is for color, since each
> pixel has a color filter over it to restrict incoming light to red, blue,
or
> green (with green being twice as common as the other two colors, since the
> eye is more sensitive to it).  So color information is significantly
> interpolated, and luminance is slightly interpolated, but the actual
> resolution of the output image overall matches that of the CCD.

Anthony,

If the color information is 'significantly interpolated' and the luminance
is 'slightly interpolated', my logic tells me that all the pixels contain
interpolated information, i.e. the info in each pixel comes partly from
neighbouring pixels.


> The Fuji case, however, inflates around 6 megapixels to twice that number
in
> the output image, and it's just as much a case of hype as are scanners
that
> "interpolate" to much higher resolutions than they can actually provide
> optically.  Pixel inflation in this way does nothing to improve image
> quality; it only helps to sell cameras to the unwary.
>
> > The skill of the camera maker is surely in choosing
> > the best size and number of sensors, their physical
> > arrangement, and the interpolation techniques.
>
> Maybe, but interpolation to twice the resolution of the chip is never
> justified for photosites of symmetrical configuration, no matter what the
> skill of the camera maker.

Surely the Fuji, with its staggered lines of sensors (similar to some Epson
scanners that have staggered lines of sensors), is an intermediate case. It
doesn't seem the same to me as the simple interpolation to massive sizes
that cheap scanners often offer. By staggering the sensors in alternate
rows, doesn't this enable better interpolations? Agreed 12 mpixel chips
would be better, but they are next years cameras.


> > For example, a Nikon D1x has a chip with 4028 x
> > 1324 sensors, but the image produced is 3008 x
> > 1960 pixels - all interpolated !!
>
> The difference is only 9.6%--still suspicious, but hardly the 100%
different
> advertised by Fuji.  The D1x has an unusual photosite configuration as
well,
> as I recall.

OK, but I wasn't calculating the overall pixel number; I was looking at the
fact that from a line of 4028 sensors collecting one side of the image, the
camera outputs 3008 pixels. And on the other side from 1324 sensors it
produces 1960 pixels. I don't see how that can be done without significant
interpolation. If it can, please explain how.

> > As to 6 mpixels being all one needs, I can see
> > the difference between my current scanned and
> > printed images with 24 mpixels and my previous
> > ones with 'only' 11 mpixels.
>
> Not on a print held at standard viewing distance.
>
> Under absolutely perfect viewing conditions, when viewing an image with an
> aspect ratio of 3:2 at a "standard" distance equal to the diagonal (about
> 3.6), you can see a maximum of 21.8 megapixels.  This limit is imposed by
> the dimensions and spacing of the cone cells in the retina, and it cannot
> get any better than this.  However, it can and does get a lot worse: under
> more normal conditions, resolving power is at least twice as bad, which
> gives a total image size of 2x2 fewer pixels, or about 6 megapixels.
>
> The only way to exceed this figure is to view the image from a closer
> distance.  The only time 6-8 megapixels is insufficient, then, is when the
> image will be viewed from less than the diagonal, or when it will be
cropped
> (the cropped portion must still have 6-8 megapixels, which means that the
> uncropped version must be correspondingly larger).

I wish people would just view images from the 'standard viewing distance';
it would make life a lot easier. But unfortunately experts always seem to
get their noses down to the prints, or even whip out their loupes, so I
reckon I need my 24 mpixels to keep them, and myself, happy.

>
> > With just 6 mpixels an A3+ print would only
> > have 167 ppi!
>
> That's all it needs, as long as you view it from at least 50 cm away.
>
> > With 24 mpixels I can send 330 ppi to the printer
> > - in the recommended range.
>
> Inkjet printers can't print more than about 150-160 ppi; the rest is for
> depth of modulation (whence the recommendation for a slightly higher
> resolution).  For large A3 prints and beyond, however, at normal viewing
> distances, you don't need that much resolution on the print.

Mmmm. I'll think a bit more about that answer.

Bob Frost.