[Radiance-general] printing floating point images

[Mark Stock]

On Wed, 1 Dec 2004, Lars Grobe wrote:

> Hi!
>
> > In general you need to print to a print device that goes direct rgb.
>
> ??? You mean a driver that can do the rgb to cmyk translation, without the
> need to do that in an application? Just wondering, I never heard about
> rgb-printers, do you mean transfering to a film (which is like foto and as
> such rgb)?
>
> Regarding printers, it is a big help to use printers that don't offer just
> cmyk, but also the light colors (there are 6 and 8 color printers), as this
> avoids raster problems in bright regions of your renderings.

This is where the Lightjet family of printers is different. They
upsample the image to ~4000dpi and expose photographic paper with
lasers. I suppose they use red, green, and blue lasers, but I
have no documented proof. I have been very happy with the output.
If you managed to make it to SIGGRAPH in the last 3 years, you
may have seen these samples of Radiance-rendered work, in
large-format, hanging in the Art Gallery.

> Calibration... afaik the radiance output is close to srgb, so if you have an
> output profile for your printer (icc), this should be easy. There is also
> macbethcal which could be used to make a simple output calibration, however,
> I never used it (I tried once).

I find that when I call a professional photo/printing business
and start talking technical, I get forwarded to the specialist,
who takes something of an interest once I mention that I have no
ICC profiles, and my work isn't from a Mac or a PC.  I've learned
that (if I set my monitor's gamma to ~2.2) what I see on my
monitor looks very much like what gets printed when I dictate
"assign no profile" or "assign sRGB." Maybe the sRGB one looks a
little more "correct," or a little less saturated. I have a hard
time telling the difference.

> I can't imagine that the bit per channel question is really relevant (for
> inkjet printing), because the limitations of paper and the raster technique
> used to mix the colors.
>
> I will have to do some large-format printouts of radiance pictures (which
> have to be rendered first ;-) for an exhibition next march, as such I am
> interested in the topic.

Another bit of advice: learn about the printer that you're using,
and send it the best possible pixels that you can. Insist that
they print at that resolution. Most printers are used to folks
printing enlargements of bad photos. It helps to talk to the
person who will actually run the machine and explain that there
is minute detail that is important. For the Lightjet 5000, I
always send a 300 dpi file, and I always antialias by pfilt'ing
my final rendering down at least 3:1 (sometimes more).

I hope my experiences have helped. It has taken me quite a few
years to learn how to "talk the talk" and get a good image
printed.

Mark