All this about fixing 'keystoning' reminds me that one technique I learned
in a 'creative printing' class in the darkroom while taking photo classes
involved fixing the keystoning by propping up one end of the paper easel.
Note that you need to use a small aperture on the enlarging lens to insure
enough depth of field to keep both ends of the image on the paper in
focus... sure is simpler to do it in software <g>.
--
Jim Brokaw
OM-'s of all sorts, and no OM-oney...
on 10/15/04 3:49 AM, Andrew Fildes at afildes@xxxxxxxxxxxxxx wrote:
>
> On the few occasions I've done it, I was adjusting one dimension I
> think. I was passing on the advice of my photo-instructor cousin who
> advised with an 'up-view' distortion (which actually gives the opposite
> of a keystone taper - I've built a rock arch!) that it was better to
> compress the base than stretch the top - although most people
> instinctively do the reverse, trying to correct what they see as the
> perspective fault at the top. He reasons that you lose information in
> the stretched area so that although it is unavoidable at times,
> compression is to be preferred. This is untested by me as yet but he
> does teach degree level and write for a couple of flashy digital
> magazines so I trust his advice.
> AndrewF
>
>
> On 15/10/2004, at 11:13 AM, Rob Harrison wrote:
>
>> On 10/14/04 2:47 AM, "Andrew Fildes" <afildes@xxxxxxxxxxxxxx> wrote:
>>
>>> Basic rule of perspective correction - always compress, never stretch.
>>
>> With the distortion typical of wides though, wouldn't one always be
>> stretching? I suppose if it was strict keystoning you were trying to
>> correct
>> you could start with the top of the building as the given and compress
>> the
>> bottom...but then wouldn't you have to stretch it again to regain
>> proportions?
>>
>>
>> LensDoc is pretty cool by the way. As Skip said, very simple and nice
>> interface.
>>
>> -Rob
>> Seattle
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