I guess we're asking the wrong question.
The question should be,
"is the pixel measurement of a reprojected, composite stitched image always meaningful?"
the answer is "no".
--- In #removed#, Fabio Bustamante <contato@...> wrote:
>
> > No matter how you try to complicate it, 6000x3000 is 18 MP, it´s simple maths. (Isaac)
>
> What a crazy discusstion in terms of lack of mutual understanding... I
> was expecting differently from this list!
>
> It is obvious that there are two absolutelly different things being
> mixed here.
>
> A 6000x3000 image will always be 18mp just like a grid of 6000x3000 will
> always have 18M squares. Arguing with that is like saying that area is
> not a product of lengh and width.
>
> The other thing in discussion is about ways of trying to measure the
> true information present in a spherical panorama, which I think is a
> very interesting topic. Actually I posted exactly this question some
> years ago, but it didn't get much attention back then.
>
> It's clear that different projections leads to different image sizes
> when you guarantee that no detail will be lost. However, remapped
> versions with extremely different sizes have exactly the same amount of
> detail, so we could drop mp as reference of image resolution of detail
> like Sacha said. Figuring a way of better measuring the detail
> resolution of a theoretical spherical image is valid to me. And the fact
> that this spherical image is composed by square pixels tells us right
> away that something can't be right.
>
> I was thinking about Mark's suggestion right before he posted it. It
> seems a good approach to the problem, to use original pixels as
> reference. IMO much better that taking an arbitrary planar projection
> and multiplying lengh by width. However even in the source images,
> pixels in theory have different relation with the sphere. We must keep
> in mind that the images we get from the camera to make the pano have
> arbitrary projection themselves. So in the case of circular fisheye
> lenses (which in theory have an f-theta projection) a square of, say,
> 20x20 pixels at the center of the image represent a very different real
> world angular area than a square of 20x20 pixels at the border of the
> circle.
>
> I thought about a different approach. Take an equirectangular image of
> 6000x3000. In theory the least distorted part of the pano is the central
> 6000px line, the horizon. The more you go up or down this 6000 wide line
> starts representing less information, up to the extreme of the top and
> bottom lines having 6000 pixels to represent a single point. But we do
> have a horizon of "pure", unstretched information.
>
> My idea is to take the horizon as a reference unit. In this case we
> would have a horizon 6000 long (not pixels, just... "units of
> information"). Then we use this number as the circunference of the
> sphere and go after the area. For this particular sphere the area would
> be of 11.459.156 (and not the 18M we get from 6K x 3K). So if this
> approach is right, the panorama represented by a 6000x3000 image would
> be roughly the equivalent of a 11.4mp image with the sharpness found on
> it's horizon.
>
> Question is: if I made this pano using a circular fisheye taking 4
> horizontal shots, can I say that this 6000 pixel wide horizon has "pure"
> information?
>
>
> Em 22/10/2010 13:18, Isaac Garcia escreveu:
> > No matter how you try to complicate it, 6000x3000 is 18 MP, it´s simple
> > maths.
> >
> > Using the same car/road example, what you´re trying to do is to say that a
> > kilometer (same in land or water :^P ) varies in the quantity of meters it
> > "holds" depending on the pavement or how much a user "enjoys" it (the
> > "representation").
> >
> > If I take a 3 MP image from my old Coolpix camera and interpolate to be 1
> > GP, it IS a 1 GP image; regardless of quality. Even if I decide to make a
> > solid white it STILL is a 1 GP image.
> >
> > It´s *simple math*, quality, proyections, aesthetics and what not have
> > nothing to say in this matter.
> >
> > Cheers.
> >
> >
> >
> > On Fri, Oct 22, 2010 at 5:06 PM, Sacha Griffin<
> > sachagriffin@...> wrote:
> >
> >> I think what you fail to see is that you consider 6000x3000 to BE the image
> >> when in fact it's a representation of the image instead.. The projection
> >> if
> >> you will.
> >> If you change projections, these numbers "6000x3000" will become a new set
> >> of numbers based on a nearly arbitrary decision about how are you trying to
> >> preserve the original detail.
> >> For example, take your gigpixel image set with 180 fov... and try to output
> >> your projection to rectilinear while trying to keep every possible
> >> detail...
> >> Based on some thoughts about it, you might end up with 1000 gigapixel image
> >> instead.
> >>
> >> Whether or not a gigapixel image is a gigapixel image is more or less up to
> >> the creator of the image and any attempts to validate it based on the
> >> dimensions of the final image is silly.
> >> Or you can simply call it a gigapixel image based on the output dimensions,
> >> but the actual detail resolution between different "gigapixel" images will
> >> still be comparing apples to oranges.
> >> A .5 gigapixel image may be far superior to a 2 gigapixel image in cases.
> >>
> >> s
> >>
> >> -----Original Message-----
> >> From: #removed# [mailto:#removed#] On
> >> Behalf Of Matthew Rogers
> >> Sent: Friday, October 22, 2010 5:24 AM
> >> To: #removed#
> >> Subject: Re: [PanoToolsNG] Re: What's a Gigapixel?
> >>
> >> But the projection is irrelevant and YES a 6000 x 3000 images regardless of
> >> it's projection or content IS 18 megapixels. Stop trying to make issues
> >> where none exist.
> >>
> >> It's the same as a megapixel, these terms are simply units that represent a
> >> quantity just like a litre, gallon, mile, kilometre etc.
> >>
> >> http://en.wiktionary.org/wiki/gigapixel
> >>
> >> It's like trying to argue how long a mile is based on the type of car and
> >> speed I'm driving to cover it.
> >>
> >> On 22 Oct 2010, at 09:33, prague wrote:
> >>
> >>> in that logic, a 6000x3000 equirect panorama is 18 megapixels.
> >>>
> >>> even though the top and bottom row of pixels (that's 18000 pixels) is
> >>> in reality TWO pixels in a spherhical projection)
> >>>
> >>> So sorry matt, everything is really not so simple, even if you would like
> >> it to be.
> >>> --- In #removed#, Matthew Rogers<matthew@> wrote:
> >>>> No it simply is not, a 6mp camera like the D70 has images which are
> >> 3000px x 2000px or 6 million pixels hence 6 megapixels. You can look at it
> >> anyway you want but a gigapixel image has to be 1,000,000,000 pixels
> >> regardless of the projection, crop etc. If the final image doesn't have a
> >> billion pixels then it aint a gigapixel image.
> >>>> I do love how panoramic photographers seem to be addicted to making
> >> things more convoluted and more difficult then necessary.
> >>>> Matt
> >>>>
> >>>>
> >>>> On 19 Oct 2010, at 20:39, Christian Bloch wrote:
> >>>>
> >>>>> Right.
> >>>>>
> >>>>> Elaborating my the chain of thought from last night, we could say
> >> that
> >> a panorama that matches the human visual field with 4 times the resolution
> >> of the human eye, is in fact a Gigapixel panorama.
> >>>>> (200 hFOV x 135 vFOV) x (200 pixels per degree)^2 = 1,080,000,000
> >> pixels.
> >>>>> Of course, that relies on the fact that Wikipedia is right about the
> >> numbers....
> >>>>> Blochi
> >>>>>
> >>>>> On Oct 19, 2010, at 11:21 AM, Bernhard Vogl wrote:
> >>>>>
> >>>>>> I'm also using the term "pixels per degree" to explain people
> >>>>>> how detailed a panorama actually is. You still can cheat by
> >>>>>> using another projection but it is very useful to explain the
> >>>>>> difference between a large and a small FOV image...
> >>>>>>
> >>>>>> Bernhard
> >>>>> [Non-text portions of this message have been removed]
> >>>>>
> >>>>>
> >>>>
> >>>>
> >>>> [Non-text portions of this message have been removed]
> >>>>
> >>>
> >>
> >>
> >> [Non-text portions of this message have been removed]
> >>
> >>
> >>
> >> ------------------------------------
> >>
> >> --
> >>
> >>
> >>
> >>
> >> ------------------------------------
> >>
> >> --
> >>
> >>
> >>
> >>
> >
>
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