HomeRoast Digest


Topic: More on CMY vs CMYK (10 msgs / 292 lines)
1) From: Kevin DuPre
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Actually your above theory deals with TRANSMITTED
light where only CMY is necessary. 100% of each of CMY
in a TRANSMITTED picture (such as on a CRT or LCD
monitor) produces black. If you check your Photoshop
resource you will see this.
Black is introduced when a computer generated image
must be printed with 4-color process printing to be
viewed under REFLECTED light. This is because process
printing uses halftone plates which have varying dot
density with the background paper which is usually
white. You can't overlay 100% of each of CMY on a
print medium and get black for reasons I previously
stated. If you want brown in varying shades (darker)
and hues (lighter), you introduce black in increasing
dot density for the former, or obviate black
completely and reduce the dot density of CMY for the
latter, letting a percentage of the white reflect
in-between the color dots to lighten the color and
produce the hues.
However the variations in whiteness of the printed
page, the various inks, and their interaction with the
printed page, the page finish (matte vs. gloss) and
the light source makes them unsuitable for
instrumentation use. 
I will reiterate that I should have qualified my
assertion that the "light source is irrelevant". A
bright light source of any kind is suitable for
comparing Agtron disks to ground coffee. Since you are
making a side-by-side comparison under the same light
for both the disk and the coffee you will obtain an
accurate comparision TO THE BEST OF YOUR JUDGEMENT. If
you color the light source with red, or green or blue
your eyes will not as easily make the comparison and
you will be fooled. The disks were not intended to be
used that way. If you have sunlight, that is probably
the best source but that depends on the time of day
for PRACTICAL PURPOSES. A bright flourescent light
will also work for making the comparison as well as
halogen bulbs commonly found in track lighting, or
incandescent floods commonly found in kitchen recessed
lighting.
What is your intended use anyway? Is the theoretical
discussion of light sources just to have a discussion,
or are you looking for how Agtron disks will be used
in a practical sense? You are not going to take a
picture of your ground coffee, process it, print it
and then compare it to the Agtron reference so why use
the same analogy for light sources.
The resulting green shift for the flourescents or
red-shift for the tungsten incandescents are
compensated for by your eyes.
I do, however disagree that there is one "best" light
source when a HUMAN VISUAL comparison is being made.
Film cannot compensate. CMYK printing is unreliable AS
INSTRUMENTATION. Unless corrective filters are used
within limits, or you use a tungsten rated film for
incandescent lights or a daylight film for sunlight or
flash the film will record a color shift and reproduce
it faithfully and it cannot be relied on for
comparison.
These are not my opinions, but a result of nearly 30
years as an amateur photographer who has spent
countless hours behind the camera and in the darkroom,
understands and has leveraged the Kodak and Ilford
published characteristic curves of both paper and film
to optimize contrast and color saturation in my
photographs, and 10 years writing software for
processing, correcting and compensating diagnostic
medical images both in color and B&W. 20 of those 30
years have also been spent as an airbrush illustrator
who has used transparency film and 4 color process
lithography to faithfully reproduce (from a color
perspective) my art for publication.
I think we've already agreed, and I agree with you
that comparison to photos or worse yet, web-published
or printed pictures are not accurate indicators for
comparison.  As previously discussed and for which
there seems to be a concensus, time, temperature, and
smell to qualify your visual perception are much
better indicators. Maintaining a log will help you
repeat the roast if you collect enough of the right
data. However if you feel that Agtron, Pantone, or
paint color chips help you make more accurate
comparisions and that is what works for you, then
great - use it :) Agtron chips for a home roaster
though, are a little pricy.
=====
--
Kevin DuPre
obxwindsurfhttp://profiles.yahoo.com/obxwindsurf"The real voyage of discovery consists not in seeking new landscapes but in having new eyes -- Marcel Proust"
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2) From: Ed Needham

3) From: Angelo
Many, many years ago, when I was in college, my friends and I decided to 
throw a party. We had very little money, but we needed to supply food. 
Since we were "decorating" with various colored lights, I decided to hang a 
green bulb over the cold cuts . The food looked disgusting. People actually 
lost their appetite when they went to get food...We had most of the food 
left over. :-)
I often see restaurants using green or blue lighting, neon being the worst. 
These restaurants are invariably empty....
A..
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4) From: Dan Bollinger
Remember the chant?  "NO BLUE FOOD!"   :)
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a
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actually
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worst.
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and
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overall
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by
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it
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compromise,
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5) From: Ed Needham
M & M's and Jell-O.  The only blue foods.
Ed Needhamhttp://www.homeroaster.comed
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6) From: Mike McGinness
From: "Ed Needham" 
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Blueberries!:-)
MM;-)
Home Ju-Ju Variable Variac Rockin' Rosto Roasting in Vancouver, WA USA
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7) From: Dave Huddle
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Blue raspberry  snowcones
Dave
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8) From: Ed Needham
Yeah...Lubos politely brought a few more 'blue' foods to my attention
offline...
"What about blueberries, the blue veins in blue cheese, blue curacaos, some
plums, some varieties of grapes, blue-purple potatoes from remote spots on
the globe, and perhaps blue jelly beans ...".
I bet there's at least a few thousand artificially colored foods that are
blue..gummy bears, etc...
Don't EVER post something you heard from someone else without checking the
facts .
"Hey, y'all... y'know, there's only two foods that are blue...Jell-O and M &
M's.
Ed Needhamhttp://www.homeroaster.comed
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9) From: Michael Scott
Sigh -- I work near a Heinz facility and on the side of one of their
buildings is a banner extolling their "electric blue" french fries...
Mds
On 9/19/02 11:52 PM, "Ed Needham"  wrote:
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10) From: John
And down here next to the border we get lots and lots of blue potatoes!
I have only had them as chips - but they sell tons of them.
On Fri, 2002-09-20 at 05:59, Michael Scott wrote:
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