mrk@gvgspd.GVG.TEK.COM (Michael R. Kesti) (03/23/89)
In article <29050@sgi.SGI.COM> donl@glass.SGI.COM (donl mathis) writes: >When i get two feet away from my monitor, it sure doesn't *seem* to be >four times as dim as when i'm one foot away! And when i'm several >miles from Halfdome, it sure doesn't seem any dimmer than when i'm >right at the base. And a light bulb doesn't seem to get any dimmer >when i back away from it. The keyword here is "seem". My camera and monitor setup and maintenance experience with my previous employer (WNMU-TV, Marquette, Mi.) taught me some very surprising lessons concerning our perception of light and color. The human eye (and its attendant processor, the brain), is very capable of "correcting" the observed scene in order to make things make sense. For example, if one color balances a camera under incandescent light, and shoots a scene containing a white object, that object will appear white both on the monitor and to the eye. If one then substitutes flourescent lighting, without rebalancing the camera, that white object will still appear white to the eye, but on the monitor it becomes decidedly blue. What happens is that our brain knows the object is white, and therefore corrects the scene to allow you to percieve it "correctly". The camera and monitor have no such ability, and therefore display the reality of the situation. A similiar phenomenon occurs in the examples cited above, within limits. Take backing away from the light bulb, for example. Take this to extremes (say back off from one foot to one mile) and of course the apparant brightness changes. Under smaller limits, however, the eye/brain combo does its best to provide useful and sensible data. I realize this only slightly relates to the discussion at hand, but I couldn't resist expounding on a subject I find fascinating and about which I know something! :-) -- ============================================================================ Michael Kesti Grass Valley Group, Inc. | "Like one and one don't make two, @gvgspd.GVG.TEK.COM | one and one make one." !tektronix!gvgpsa!gvgspd!mrk | - The Who, Bargain
network@mstr.hgc.edu (craig chaiken) (03/29/89)
In article <698@gvgspd.GVG.TEK.COM>, mrk@gvgspd.GVG.TEK.COM (Michael R. Kesti) writes: > In article <29050@sgi.SGI.COM> donl@glass.SGI.COM (donl mathis) writes: > >When i get two feet away from my monitor, it sure doesn't *seem* to be > >four times as dim as when i'm one foot away! And when i'm several > >miles from Halfdome, it sure doesn't seem any dimmer than when i'm > >right at the base. And a light bulb doesn't seem to get any dimmer > >when i back away from it. A light source does not get dimmer as you move away from it. If this were the case, then the moon would be very dim. Rather, the surface area lit by the source becomes dimmer with increasing distance. The reason is that the light source is spread over an increasingly large surface area. If you focus an image of the moon through a lens, however, it will be equally bright (more or less) from any distance. Craig Chaiken Hartford Graduate Center Computing Services