Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!iuvax!purdue!mentor.cc.purdue.edu!pur-ee!3ksnn64 From: 3ksnn64@pur-ee.UUCP (Joe Cychosz) Newsgroups: comp.graphics Subject: Re: photographing screens Message-ID: <13597@pur-ee.UUCP> Date: 28 Nov 89 23:01:00 GMT References: <3777@hydra.gatech.EDU> Reply-To: 3ksnn64@pur-ee.UUCP (Joe Cychosz) Organization: Purdue University Engineering Computer Network Lines: 153 In article <3777@hydra.gatech.EDU> robert@shangri-la.gatech.edu (Robert Viduya) writes: >Has anyone advice or pointers to information on how to photograph video >screens? I'm trying to shoot the screen of an SGI 4D/120GT. I have a SGI here, and shoot most of my slides/prints from it. >experimented with a Canon AE-1 with shutter speeds of 1/15 sec and 1/8 >sec and let it choose the aperature. I was also using ASA 400 film. I don't know how you have configured your Canon (I assume AE means some form of automatic). I would set the speed and aperature manually as described below. Also, get rid of the 400 speed film, it is too grainy and has poor color properties for this application. Use 100. >The results left a bit to be desired. I lost a lot of red tints >except where the color was solid red and then it stood out too much. >A lot of fine detail was lost as well. I probably should've used a >lower film speed like possibly ASA 200. These are all properties of using 400 speed film and printing problems. > I also suspect that the color >balance was screwed up in the development process and I was wondering >what I could do to prevent that in the future (I don't do my own >development). I think you mean printing and not the developing of the film. This is probably the most crutial step. The expose time and aperature settings are fairly forgiving for ASA 100 film. It is in the printing where the color is realy determined. Below discusses printing on comercial machines. Since you are doing your own work, I can't help much other than suggesting that you determining what is the equivalent of density in your printing process. Here is my guide to photographing computer graphics displays. This was posted a while ago in comp.graphics. I have updated it some to discuss the problems of the Nikon 70-210mm lens and some printing info on specific machines. ---------------------------------------------------------------------- Film: I use Kodak ASA 100 print film for prints and Ektachrome ASA 100 (Ektachrome 64 is no longer available) for slides. 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 at 70mm. This contradicts what one might think in that one would expect the flattest photo to appear by getting as far away as possible and shooting with as long of a lens as possible. The problem is in the distoration in the lens system at 210mm. Keep in mind that a macro lens works on a series of approximations. What results is concave pillowing which is oppisite of the convex pillowing caused by the curvature of the screen. The optimal flat picture occurs when the convexed pillowing of the screen is balanced with the concaved pillowing of the distortion in the lens system. Since I do not have a straight 200mm lens, I have not been able to study and measure the distortion in the macro. One final note: I tend to shoot images that are either 640x480 or 512x 512 off of the SGI. I have shot full screen images, but the curvature of the screen gets a bit difficult to control, especially with the 70-210 lens problems. 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 ASA 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, 1/60th. A wide black bar will appear on the screen. 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. I have shot 1 second exposures at f8 and have had similar results out of a sugestion of Craig Good at Pixar. Again, ASA 100 speed film is pretty forgiving. I have found the exposue metering systems in cameras to unreliable when determining the exposue. This is especially true when shooting vector displays. Also, you want to avoid full white areas such as menu areas and the like. Change them to a 70 - 80% grey. The pictures will look much nicer when printed. 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 and fully saturated colors. Vectors are the hardest to process. I use a Noritsu and a Fuji machine for my processing. Usually one or two units of density must be added (i.e., +1, +2) for computer graphics shots. The process you are going through is to balance the quality of the color with the quality of black. If you don't do this you will end up with brown instead of black. The Noritsu and Fuji will will print on the back of the photo what settings were used. So if you do reprints bring the old photo in so the processor can see what settings they used last time. Examples follow below: Noritsu: 896 45 N N N 6 2 896 = Sequence number 45 = Film code (45 = Kodak 100) N N N = Yellow, Magenta, Cyan print levels. N = neutral, there will be numbers -1, +1, etc. for non-neutral settings. 6 = Density setting. 2 = Ignore. Fuji: 79 010005 28 +01 +0 -01+02 NN -5 0 79 = Sequence number. 010005= Film/vendor/speed code (Kodak 100) 28 = Daily density setting, results from calibration. +01 = Density setting. +0 -01+02 = Cyan, Magenta, Yellow print leves. +0 = neutral. NN = Ignore. -5 0 = Ignore. 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 am in the process of working on a calibration image which will help the process people make there settings. I am also working on reducing the yellow edges which appear (especially at red and green boundries). I don't expect to have any of this done sometime soon though. Brought to you by Super Global Mega Corp .com