tada@athena.mit.edu (Michael Zehr) (11/12/88)
I've been having difficulties photographing color images on a computer screen and developing them. I'm working with a color vaxstation, and using Kodak kodachrome film. What I see on the screen isn't being reproduced exactly on the film. Red looks orange, blue looks lighter, green looks yellowish. I've tried talking to photo stores and developers, and so far none of them has been able to help, but i figure someone reading this has tried to take color photos from a screen before. I'm not certain yet what the source of the problem is. I know that what the eye sees as a color is a combination of the actual hue, which is probably composed of several spectral lines from the phosphor. The fact that it's blinking at 50 or 60hz also changes what you see. Some of the photo places have pointed out that the automatic color balancing by the machine developers may throw the color off as well. Does anyone have any suggestions about what to do? Any help would be greatly appreciated. Thanks in advance. -michael j zehr
klee@daisy.UUCP (Ken Lee) (11/12/88)
Sounds to me like you're overexposing your film. Try bracketing.
Also, to avoid screen flicker, take a relatively long exposure in a
very dark room. The exposure that's right for you will, of course,
depend on your particular monitor, but 0.5 second at f/8 (I assume
you're using 35mm film and a 50mm lens) should be a good starting
place with Kodachrome 64 film. Use a good tripod and cable release.
I've had no trouble, using the standard Kodak processing.
If this still doesn't work, you may want to change your monitor's
color balance. I've heard that some people turn up the red "a little".
Ken
--
uucp: {ames!atari, ucbvax!sgi, pyramid, uunet}!daisy!klee
arpanet: daisy!klee@sgi.com or daisy!klee@uunet.uu.net
I'm not a tourist, I was born in California.rwi@naucse.UUCP (Robert Wier) (11/12/88)
Some time ago (I think it was at SIGGRAPH '81), I got a sample
roll of film from (I believe) GAF (or was it AGFA?) that was
supposedly formulated to better approximate the color phospers
of a CRT than regular film. Since I never used it, I MAY be
able to find it to post the actual number, if anyone is interested,
or perhaps someone out there knows if it is still being made and
what the exact designation is.
-Bob Wier at Flagstaff, Arizona Northern Arizona University
College of Engineering *usual disclaimers*
NAU Box 15600 ...arizona!naucse!rwi
Flagstaff, Az. BITNET: WIER@NAUVAX
86011 602-523-2052
(note: Bitnet node NAUVAX may not be
known yet to all stations)
College Motto: "The highest level of engineering in the Southwest
(7,000 feet)"annala@neuro.usc.edu (A J Annala) (11/12/88)
You might also want to try using some of the new PolaChrome HGX high contrast instant color slide film which is specially made for photographing color graphics screens. AJ Annala, USC Neural, Informational & Behavioral Sciences Program
bellutta@irst.UUCP (Paolo Bellutta) (11/14/88)
>I've been having difficulties photographing color images on a computer screen >and developing them. I'm working with a color vaxstation, and using Kodak >kodachrome film. What I see on the screen isn't being reproduced exactly >on the film. Red looks orange, blue looks lighter, green looks yellowish. ... >-michael j zehr Alorithm: Put a cardboard-box in front of the monitor, set luminance and contrast to the lowes level but in a way that all grey levels / colors are visible. Cut a round hole on the bottom of the box so that the lens of the camera can be slided through. Use a reflex camera on a tripod. You can use normal lenses (50mm) but to avoid distorsion of straight lines a short telephoto (75-80mm) whould be better but you need a larger box since telephoto lenses have 1 - 1.5 mt. as minimum distance. Use a 100 - 200 ASA color slides film and then if you need prints you can have them using Cibachrome. Shutter speed should be 1/4 sec. (= 0.25 sec.). Aperture depend on the picture brightness and you can trust the exposimeter. You can use the self timer to avoid moving the camera when taking the picture. This is the procedure I'm following for taking pictures of comp. screens (used on Vax, Apollo, Sun ...). Remember that the quality of the slide depends on the quality of the monitor and for a minor part on the quality of the lenses of your camera. Never expect to have the same results of the slide on print since this has less contrast. Good luck. Paolo Bellutta I.R.S.T (Institute for Scientific and Technological Research) via della Cascata 38050 POVO (Italy) phone: +39 461 810105 fax: +39 461 810851 -- Paolo Bellutta
anson@spray.CalComp.COM (Ed Anson) (11/14/88)
In article <7896@bloom-beacon.MIT.EDU> tada@athena.mit.edu (Michael Zehr) writes: >I've been having difficulties photographing color images on a computer screen >and developing them. I'm working with a color vaxstation, and using Kodak >kodachrome film. What I see on the screen isn't being reproduced exactly >on the film. Red looks orange, blue looks lighter, green looks yellowish. Yes, this can be difficult. A few things to try: The color results you are getting indicate an improper color balance for the film. This is a function of the phosphors in your CRT. Try a film designed for tungsten light. It should be available from any good photo store. If you're really picky about the colors, you may need some color correction filters (but that's a lot of trial and error). Also, make sure you're using a fairly fast film. Try for an exposure in the range of 1/30 to 1/15 second. Longer exposures cause some reciprocity failure, which affects the different primaries differently. Fortunately, most tungsten balanced films are also fairly fast, since they're intended for indoor use. > >I've tried talking to photo stores and developers, and so far none of them has >been able to help, Most of those folks have never seen a computer screen, much less photographed one. :-) > >Some of the photo places have pointed out that the automatic color balancing >by the machine developers may throw the color off as well. I've never heard of automatic color balancing of Kodachrome. That's something they do with prints. > >Does anyone have any suggestions about what to do? Any help would be >greatly appreciated. Thanks in advance. I hope this helps. > >-michael j zehr Ed Anson -- ===================================================================== Ed Anson, Calcomp Display Products Division, Hudson NH 03051 (603) 885-8712, anson@elrond.CalComp.COM
brianm@sco.COM (Brian Moffet) (11/15/88)
I have found that a sliht telephoto will do better for
photographing a picture tube than a 50 mm lens.
I use a 110 or 135 to photograph my 13 inch Sony
monitor hooked up to my amiga.
I also must say this, I do not have a flat screen,
it does bow out at the edges. I telephoto helps keep
the perpsective on the screen somewhat flat. If you
use a wide angle, the screen looks less square
the shorter the lens you use. (insert appropriate
photographic term here, I can't remember it )
Basically, I would recommend using a zoom to see what various
things look like, then transfer to a fixed focal length.
IMHO the fixed length lenses are better for this work.
Please, do not barrage me about why this may not be true. :-)
brian m.
--
Brian Moffet {uunet,decvax!microsoft,ucscc}!sco!brianm
-or- ...sco!alar!brian
"Evil Geniuses for a better tomorrow!" My fish and company have policies.
I have opinions.dregis@pldote1.intel.com (~Dave Regis) (11/15/88)
I found that when photographing CRTs, the use of a lens with a long focal
length helps considerably. I use a 100mm lens, at a distance of 6 ft (this
will depend on the size of the CRT). Using this configuration does not
produce any distortion inherent with 50mm or less lenses. I try for a shutter
speed of 1/15 or less; the brightness should be turned down so that in a
completely darkened room, black looks black. As far as film goes, ISO64
Kodachrome (or equivalent slide film) reproduced colors faithfully. (The
importance of a completely darkened room cannot be stressed. Reflections
not seen by the eye become readily apparent on film!)
Dave Regis
(Prof. Grace Hertlein at CSU Chico was of great assistance in achieving
perfect results.)watson@ames.arc.nasa.gov (John S. Watson) (11/16/88)
[this discussion started in comp.graphics] Here's how I get 24 bit photographs of my images from my 8 bit Sun screen (The basic idea is to triple expose the film, once with each R,G,B channels). First I set up my 35mm camera in front of the our Sun's 8-bit color monitor, on a tripod. I level the Sun screen and make sure the camera is pointed at the center of the Sun screen. A good sturdy tripod is best, but I use my ultra-cheap ultra-lite backpacking tripod. I also connect my remote shutter controller, and turn on the 2 second delay to minimize vibrations. I use a telephoto lens of about 100mm to minimize the "wide-angle" distortion. Once everything is set up I run a program I wrote that take the three red, green and blue image files and make a grey scale "intensity" file. Then I display this intensity image. Next, I turn out all the lights in the room and take a meter reading of the intensity image. I have a fancy camera that has all sorts of automatic modes, but I just use it's light meter to tell me the right exposure. I use as slow a film as 100 ISO or less, usually Kodak. I want a long shutter speed to avoid flicker, on the order of 10 seconds, so I set the aperture to 8 or more. Next I set my camera to expose the same frame 3 times, and set the exposure to 1/3 of the meter reading I got from above (so for the 10 second example I'd expose with three 3.33 second exposures). I have 3 little programs with display each of the red, green and blue file separately, each with it's respective "red scale", "blue scale" and "green scale" colormap (i.e., for the "red scale" the red values in the colormap are from 0 to 255, and the green and blue are 0). So then I: Display the red channel. Expose the film. Display the green channel. Expose the film. Display the blue channel. Expose the film. That's it. I also redo the whole process at with a slightly longer and at a slightly shorter exposure (bracketing), just in case. Turn on the lights, go home, have a beer. I'm sure there are lots of nitty gritty details that I ignore; things like gamma corrections of the monitor and all that sort of stuff, but what the heck, the results are fine. Have fun, -- John "Crash" Watson, Civil Servent from Hell ARPA: watson@ames.arc.nasa.gov NASA Ames Research Center UUCP: ...!ames!watson Any opinions expressed herein are, like, solely the responsibility of, like, the author and do not, like, represent the opinions of NASA or the U.S. Government.
kurtk@tekcae.CAX.TEK.COM (Kurt Krueger) (11/18/88)
I've seen some good advice here, but thought I would add some more info. Notice that camera systems designed for this work are set up to photograph a black and white screen through 3 different color filters (i.e. the red part is displayed and photographed through a red filter, etc.) This solves a few problems. 1. The mismatch of the color phosphor's output spectrum vs. the film's spectral response is fixed by the color filters. 2. Gamma correction can be done, as well as differing sensitivity to the three primary colors. 3. If you take a magnifying glass to the color screen, you will notice that if you have an entire green image (for example) that only 1/3 of the screen is actually lit up (the red and blue dots are black in this case). A well focussed photograph will be 1/3 green and 2/3 black. The results will be a muddy green. By photographing a b&w screen through a green filter you can get 100% green. (Note: you can help this situation by overexposing or defocusing).
prc@ERBE.SE (Robert Claeson) (11/18/88)
In article <2496@spray.CalComp.COM>, anson@spray.CalComp.COM (Ed Anson) writes: > In article <7896@bloom-beacon.MIT.EDU> tada@athena.mit.edu (Michael Zehr) writes: > >I've been having difficulties photographing color images on a computer screen > >and developing them. I'm working with a color vaxstation, and using Kodak > >kodachrome film. What I see on the screen isn't being reproduced exactly > >on the film. Red looks orange, blue looks lighter, green looks yellowish. > Also, make sure you're using a fairly fast film. Try for an exposure in the > range of 1/30 to 1/15 second. Longer exposures cause some reciprocity failure, > which affects the different primaries differently. Don't use an exposure time that's shorter than the refresh time of the screen, or else you'll just get a partial screen on your slide. I'd recommend 1/8th second. That's what I use with Kodak's Ektachrome 160 Professional. -- Robert Claeson ERBE DATA AB rclaeson@ERBE.SE
raveling@vaxb.isi.edu (Paul Raveling) (11/19/88)
In article <7896@bloom-beacon.MIT.EDU> tada@athena.mit.edu (Michael Zehr) writes: >Some of the photo places have pointed out that the automatic color balancing >by the machine developers may throw the color off as well. Some screen image pictures I did earlier this week suggest this is the prime culprit. It also turned out that a few images got suboptimal exposures when there was either a dark or light area at the center of the frame; that's due to the camera using center-weighted averaging for automatic exposure. It's possible to anticipate this by guestimating how much each zone of the image will influence metering, but bracketing is still the safest approach. Another source of amusement is Moire patterns in the finder. At some distances the granularity of the raster and the focusing screen's Fresnel lens match closely enough to generate colored patterns. --------------------- Paul Raveling Raveling@vaxb.isi.edu
good@pixar.uucp ("It's kind of fun to do the impossible." -- Walt Disney) (11/21/88)
In article <18196@ames.arc.nasa.gov> watson@ames.arc.nasa.gov (John S. Watson) writes:
:
:[this discussion started in comp.graphics]
:
:Here's how I get 24 bit photographs of my images from my 8 bit Sun screen
:(The basic idea is to triple expose the film, once with each R,G,B channels).
You can also get pretty good results just shooting off the monitor. I
routinely make slides here with Ektachrome 100 and a 200mm Macro Nikor.
Off our Barco and Sony RGB monitors I wind up with 1 second at f5.6.
Back in 1984 I shot "The Adventures of Andre & Wally B" by setting a
Mitchell with an animation motor right in front of a 512 x 488 Barco.
It turned out better than it should have.
Better systems will get you better pictures, but you'll be amazed
how well simple setups work.
--Craig
...{ucbvax,sun}!pixar!goodflip@pixar.UUCP (Flip Phillips) (11/22/88)
In article <2709@pixar.UUCP> good@pixar.uucp ("It's kind of fun to do the impossible." -- Walt Disney) writes: >In article <18196@ames.arc.nasa.gov> watson@ames.arc.nasa.gov (John S. Watson) writes: [...] > [...] >Back in 1984 I shot "The Adventures of Andre & Wally B" by setting a >Mitchell with an animation motor right in front of a 512 x 488 Barco. When I was at Ohio State CGRG we shot all of the films using an Ariflex 16mm with an animation motor, shooting directly off of the monitors. We would use Ektachrome News stock, as I recall, cant recall the stock number, maybe someone who remembers can pass it along. >It turned out better than it should have. So did ours. -- Flip Phillips {sun | ucbvax}!pixar!flip Pixar - Marin County, California
dave@onfcanim.UUCP (Dave Martindale) (11/23/88)
In article <18196@ames.arc.nasa.gov> watson@ames.arc.nasa.gov (John S. Watson) writes: > >Once everything is set up I run a program I wrote that take the three >red, green and blue image files and make a grey scale "intensity" file. >Then I display this intensity image. Next, I turn out all the lights in >the room and take a meter reading of the intensity image. A much simpler method: fill the screen with full-intensity white. Take a light meter reading. Increase exposure by 2.5 stops. This puts the brightest whites near the upper end of the linear portion of the response curve for slide film. With negative film, you might give just a bit more exposure if you want more shadow detail. (Note that 2**(-2.5) = 0.18, and thus that this method is also equivalent to displaying and reading an 18% grey patch, except that by using white you can get away with a less-sensitive light meter, and also don't have to worry about how well your gamma correction has been done - i.e. whether your 18% grey is really 18% of white). >I want a long shutter speed to avoid flicker, >on the order of 10 seconds, so I set the aperture to 8 or more. Most films recommend using colour filters to correct for colour shift due to reciprocity failure with such long exposures. An exposure time of 1 second seems a good compromise - long enough that you don't see a dark bar due to recording a non-integral number of video fields, but short enough not to worry about reciprocity problems. >Next I set my camera to expose the same frame 3 times, and set the >exposure to 1/3 of the meter reading I got from above (so for the 10 second >example I'd expose with three 3.33 second exposures). This is wrong - you should use the same exposure, not 1/3 of it. Your light meter tells you to expose the film to the full-colour image for, say, 1 second. If you had a 24-bit frame buffer, you would do exactly that. Since you have just 8 bits, you do each colour separately, but you still need 1 full second of red, 1 second of green, and 1 second of blue to give the same exposure as 1 second of white.
3ksnn64@pur-ee.UUCP (Joe Cychosz) (11/26/88)
In article <2709@pixar.UUCP> good@pixar.uucp ("It's kind of fun to do the impossible." -- Walt Disney) writes: >In article <18196@ames.arc.nasa.gov> watson@ames.arc.nasa.gov (John S. Watson) writes: >: >:[this discussion started in comp.graphics] >: >:Here's how I get 24 bit photographs of my images from my 8 bit Sun screen >:(The basic idea is to triple expose the film, once with each R,G,B channels). > >You can also get pretty good results just shooting off the monitor. I >routinely make slides here with Ektachrome 100 and a 200mm Macro Nikor. >Off our Barco and Sony RGB monitors I wind up with 1 second at f5.6. I agree, however I use a few different settings. I also shoot Ektachrome 100 (Ektachrome 64 is no longer available). For prints I use standard Kodak 100 print film. Setup: This is the longest and most crucial step. It is important to get the lens as perpendicular as possible to the screen. Things to watch for are monitors which tilt (like Suns or SGIs). I also try to get the lens as close as possible to the screen and still be able to focus. This helps reduce the effects of the curvature of the screen. For a 70-210mm Macro Nikon this is about 2 ft. Exposure: I use a 1/2 second exposure at f8 with half a stop added in. To bracket the exposure I also shoot a f5.6 and a f11 exposure. With 100 speed film the exposure can be fairly forgiving. That is to say, you'll get a reasonable picture as long as the exposure and f-stop are within reason. Never shoot faster than the refresh rate of the monitor. This even goes for taking pictures of monitors sitting in rooms. If you do you will endup with black bars on the screen. For room shots I use 1/8 second or longer. Processing: For prints I usually tell the people that process my film that the roll contains computer graphics. Many film printers are computered controlled and are setup for printing people, sky, grass, trees and other things which you would find in normal photos. These printers usually lose it when the get a picture with lots of black. Vectors are the hardest to process. One other problem the film processing machines have is alignment. Lets say you are shooting pictures of some square 512x512 images. The film processor will more than likely assume that the left edge of the image is the left edge of the picture. I will not center it for you. This will also happen with slides. To solve this problem two things can be done. One: shoot a few fully exposed pictures at the beginning of the roll so the machine can set where the left edge is for the rest of the roll. Or two: us an alignment background pattern like I do. This looks something like this: ---------------------------------- ! ! ! ! ! ! ! ----------------- ! ! ! ! ! ! ! ! ! !-------! Image ! ! ! ! ! ! ! ! !--------! ! ! ! ! ! ----------------- ! ! ! ! ---------------------------------- I'll have to try a 1 second exposure at f5.6 in the next roll I shoot. Joe Cychosz
cnsy@vax5.CIT.CORNELL.EDU (11/29/88)
I passed on the film comments on comp.graphics to our documentation expert, Paul Booth, and he replied to me: First (with apologies to the great Yellow god of Rochester), neither Kodachome nor Ektachrome, in our experience, successfully handle graphics screens. Both want to shift the entire image way over toward cyan (blue). 100 ISO/ASA Fujichrome does a MUCH better job of correctly reproducing the colors on the screen. The blue shift is eliminated, and overall color rendition is far better than Kodak's, though I think the reds can be a little wimpy unless the slide is slightly underexposed. This has held true for both 35mm and 4x5 slides. A good starting exposure for 35mm Fujichrome (or Ektachrome, if you must) is 1 second at f/8. Bracket this base exposure in 1/2 stop increments for 1.5 stops in each direction to make sure that you get a good shot. Also, you should always avoid exposures over 2 or 3 seconds -- a nasty photo demon called reciprocity failure starts to kick in on exposures longer than this, causing colors to shift and exposure relationships to fall apart. Believe me, 8 sec at f/32 is NOT the same as 1 sec at f/8 with color slides! Second, definitely use a longer lens, if you have one, to reduce the distortion caused by the curvature of the screen. A lens in the 100mm to 150mm range is best. -- PBB Hope this adds some worthwhile info to the discussion, Eric Haines (still not John Saponara), ...!hplabs!hpfcla!hpfcrs!eye!erich
billd@celerity.UUCP (Bill Davidson) (12/02/88)
In article <9900@pur-ee.UUCP> 3ksnn64@pur-ee.UUCP (Joe Cychosz) writes: ..... >monitors which tilt (like Suns or SGIs). I also try to get the lens as >close as possible to the screen and still be able to focus. This helps >reduce the effects of the curvature of the screen. For a 70-210mm Macro >Nikon this is about 2 ft. Er, that's not what I learned in photography school. You can't totaly eliminate curvature but it is definitely INCREASED by getting closer. Your best bet should be to get as far away as possible. Since you will still want to nearly fill your frame, the distance will be dictated by the length of lenses you own (and the amount of space available in front of your screen :-) Shooting from far away with a long lens flattens any picture. --Bill Davidson -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ....!{ucsd|sdcsvax}!celerity!billd