Digital BW, The Print

----- Original Message -----
From: "Anthony Atkielski" <atkielski@...>
To: <DigitalBlackandWhiteThePrint@yahoogroups.com>
Sent: Wednesday, July 31, 2002 2:34 AM
Subject: Re: [Digital BW] Storage of digital images


> 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.
>
> Additionally, most interpolation does not inflate resolution artificially.
> If anything, in good cameras, the resolution in the output image is
_lower_
> than the resolution of the CCD, because interpolation is used to produce a
> smaller number of pixels of better quality.
>
> 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.
>
> > 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.
>
> > 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).
>
> Most small prints are actually viewed from distances larger than the
> diagonal, and so the required number of pixels is even smaller.  For a
> 4x6-inch snapshot viewed from 19" away, even one megapixel is fine.
>
> On the other hand, if you make a wall-sized 6x6-foot enlargement and view
it
> from two feet away, you'll need 106 megapixels (more than 10,000 pixels on
a
> side) in the image in order to guarantee that it looks sharp from that
> distance.  This requires at least medium-format gear.
>
> > 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.

Anthony,

The problem is that the artist generally has no control over the viewing
distance. With small prints I think your theory is probably sound but with
large prints I think there are practical problems. People are going to walk
right up to that 6x6 foot print and view it at 18". Worse they might be
extremely nearsighted, like myself. When I take my glasses off I can look at
a portion of the print from a distance of about 4". (That's not really fair
to the artist but I can't resist. <G>)

Realistically I would expect people to hold large prints 11x17 to 20x24 up
in their hands to look at them at distances of say 12" to 24". In a gallery
situation I would want to be prepared for people to look at my prints at
least 18", probably 12", regardless of size.

I have never heard anyone recommend input to an inkjet below about 240 ppi
which corresponds to 1.5 x 160 ppi. A more common rule of thumb is 360 ppi.
Beyond that I cannot detect any significant difference but others report
that they do see a difference by going to 720 dpi.

For myself I would like the image quality of my inkjet prints to be equal to
my silver fiber prints and this seems to require 360 ppi to the printer
regardless of print size. Since the largest I can print with my 1280 is
13x19 this leads me to a minimum file size of about 30 megapixels or if I
want my file to be capable of being printed at 20x24 about 60 megapixels.

Now I am quite impressed by some of the B&W prints I have seen from cameras
like the DX1 enlarged to 13x19 and at a normal viewing distance of 23" or
greater I think they are very appealing. The grainless characteristics give
the prints a large format feel rather than a 35mm feel. View them at a
closer distance and the lack of fine detail becomes noticeable to me. Keep
in mind that I favor a 4x5 view camera for my work so that you have an idea
of what I like to acheive with my own prints.

Martin Wesley