Search found 19 matches

by Mark Sirota
2011-06-23T10:56:43-07:00
Forum: Users
Topic: Algorithmic vignetting correction for pinhole cameras?
Replies: 13
Views: 48463

Re: Algorithmic vignetting correction for pinhole cameras?

Apologies for the long delay... i would not discount the effect of light angle though the pinhole. that 71% reduction at the side edges of a P90 film is not to be taken lightly. And that effect is doubled for the Y direction. This is of course on top of the Y distance effect! I've been giving this a...
by Mark Sirota
2011-06-16T17:52:19-07:00
Forum: Users
Topic: Algorithmic vignetting correction for pinhole cameras?
Replies: 13
Views: 48463

Re: Algorithmic vignetting correction for pinhole cameras?

All true regarding other sources of vignetting for pinholes. The best pinholes are drilled with beveled edges rather than as cylinders to minimize this, and some people are making them out of clear film now, with a black coating except in the pinhole area. These don't work as well with very wide ang...
by Mark Sirota
2011-06-16T16:05:59-07:00
Forum: Users
Topic: Algorithmic vignetting correction for pinhole cameras?
Replies: 13
Views: 48463

Re: Algorithmic vignetting correction for pinhole cameras?

That looks more like it. How about separating horizontal from vertical? For example, a camera with a curved film plane would have vignetting in this pattern along the Y axis, but none on the X axis.
by Mark Sirota
2011-06-16T11:51:36-07:00
Forum: Users
Topic: Algorithmic vignetting correction for pinhole cameras?
Replies: 13
Views: 48463

Re: Algorithmic vignetting correction for pinhole cameras?

Do be more clear, 1/((d/ƒ)^2) is the amount of light received at that location.

Your image doesn't look like real falloff. It's too uniform in the center, and the contrast is too high/sharp at the edge of your circle.
by Mark Sirota
2011-06-15T23:03:58-07:00
Forum: Users
Topic: Algorithmic vignetting correction for pinhole cameras?
Replies: 13
Views: 48463

Algorithmic vignetting correction for pinhole cameras?

After being so impressed by this community following the Correcting for a curved film plane? discussion, I've got a followup to ask... Pinhole cameras generally need significant vignetting correction. They tend to have very wide angles of view, which means that the corners of the frame are much furt...
by Mark Sirota
2011-06-15T22:42:14-07:00
Forum: Users
Topic: Correcting for a curved film plane?
Replies: 62
Views: 122072

Re: Correcting for a curved film plane?

Anthony, thank you thank you thank you for implementing this in 6.7.0-8. I'm really impressed by this community!

Next up -- algorithmic vignetting correction for scans from pinhole cameras. I've started a new thread.
by Mark Sirota
2011-06-15T08:02:20-07:00
Forum: Users
Topic: Correcting for a curved film plane?
Replies: 62
Views: 122072

Re: Correcting for a curved film plane?

Sorry, I'm still here. I don't know the FOV of that mail boxes image; I assumed it was the full frame from a P.90. But the photographer is not replying to my queries, and I don't yet own one of these things. I have plans to build one...
by Mark Sirota
2011-06-11T08:36:12-07:00
Forum: Users
Topic: Correcting for a curved film plane?
Replies: 62
Views: 122072

Re: Correcting for a curved film plane?

Yes, it looks to me like that shot had pointing slightly down. That's why I was excited about that other shot I found, which had lots of straight lines -- but while the owner has said it's okay to use it, he hasn't made it available to download and has not responded to my latest request. In any case...
by Mark Sirota
2011-06-07T11:39:28-07:00
Forum: Users
Topic: Correcting for a curved film plane?
Replies: 62
Views: 122072

Re: Correcting for a curved film plane?

fmw42 wrote:Also see my numbers above on how fast the image size grows with fov. By 160 degrees its area is about 16 times as big as the input.
Is that a problem?
by Mark Sirota
2011-06-07T11:20:53-07:00
Forum: Users
Topic: Correcting for a curved film plane?
Replies: 62
Views: 122072

Re: Correcting for a curved film plane?

I would not be surprised it may be that it is actually engineered to be 90 degrees, but with 57mm being a near approximation (for advertising). We would need to know for certain! Actually the specs on the reference page say it is nearly 90 degree field of view and give a specific focal length of 57...
by Mark Sirota
2011-06-06T17:42:43-07:00
Forum: Users
Topic: Correcting for a curved film plane?
Replies: 62
Views: 122072

Re: Correcting for a curved film plane?

Awesome. These don't seem to take into account the half-pixel error mentioned earlier by Anthony, right? The owner of the photo I mentioned earlier has given his permission for us to use his photo as a test, but unfortunately he hasn't set the permissions at Flickr such that we can download it. Can ...
by Mark Sirota
2011-06-06T10:58:04-07:00
Forum: Users
Topic: Correcting for a curved film plane?
Replies: 62
Views: 122072

Re: Correcting for a curved film plane?

Great work and many thanks, everyone who has participated!

I found a much better test photo on Flickr, and have asked permission to use it and post here. I'll let you know.
by Mark Sirota
2011-06-04T19:35:26-07:00
Forum: Users
Topic: Correcting for a curved film plane?
Replies: 62
Views: 122072

Re: Correcting for a curved film plane?

Yes, that last bit (your P.S.) is exactly right. The top and bottom of the corrected image would be concave. (Presumably, this would then be cropped back to a rectangle, as indicated in my diagram.)
by Mark Sirota
2011-06-03T21:30:28-07:00
Forum: Users
Topic: Correcting for a curved film plane?
Replies: 62
Views: 122072

Re: Correcting for a curved film plane?

The Y axis must stretch as well, and it must stretch further as you move away from center. Here's a quick diagram (I did it in Sketchup rather than ImageMagick, which is shameful, but it's past my bedtime and I'm faster in Sketchup): http://www.sirota.org/mark/photography/curved.png As you can see, ...
by Mark Sirota
2011-06-03T18:52:43-07:00
Forum: Users
Topic: Correcting for a curved film plane?
Replies: 62
Views: 122072

Re: Correcting for a curved film plane?

Fantastic, thank you! It looks like you've corrected for the X axis, but not the Y. I've worked out the math for the X axis somewhat differently than you did, at least I think it's different. I need to work out your formula. Assuming the image center is at 0,0 and x1,y1 is the location of an origina...