[FFmpeg-devel] [PATCH 4/4] avfilter/vf_v360: refactor (i)flat_range for fisheye
Daniel Playfair Cal
daniel.playfair.cal at gmail.com
Tue Mar 23 06:00:45 EET 2021
What exactly is your definition of fisheye?
The definition I'm working with is the equidistant fisheye projection as
described here: https://wiki.panotools.org/Fisheye_Projection, i.e. r = f *
theta
That mapping works for any theta, and you can have a circular image with a
field of view of up to 360 degrees before anything is repeated and the
inverse mapping is ambiguous. Hence my assumption that a rectangular output
image with a 180 horizontal/vertical field of view should still contain
areas near the corners where theta > 90 (because the diagonal FoV is >
180), and these should still be mapped from such an image to a
equirectangular projection.
Do you prefer for some reason to limit the fisheye projection to 180
degrees on any axis, i.e. have the constraint that theta <= 90? If that's
the case I could patch xyz_to_fisheye and fisheye_to_xyz so that such areas
are marked as invisible? That causes your example filtergraph to work as
before.
On Tue, Mar 23, 2021 at 3:46 AM Paul B Mahol <onemda at gmail.com> wrote:
>
>
> On Mon, Mar 22, 2021 at 1:35 PM Daniel Playfair Cal <
> daniel.playfair.cal at gmail.com> wrote:
>
>> > I disagree, if I use 180 hfov and 180 vfov it should not have extra
>> areas but only half of previous input.
>>
>> Not sure I follow - the ih_fov and vh_fov refer to the input (i.e. the
>> fisheye image). If you wanted to restrict the FoV of the output, surely the
>> way to do that would be to implement and use the FoV settings for the
>> equirectangular projection?. It doesn't seem right that the code for the
>> input projection is responsible for deciding what appears in the output. My
>> understanding was that the FoV settings simply describe the focal length of
>> the input or output camera so that points in the images can me mapped
>> to/from 3d coordinates.
>>
>>
> Take any equirectangular input and convert it to fisheye and than back to
> equirectangular.
> Or just take pure fisheye input with 180 h & v fov and convert it to
> equirectangular. There is plenty of such video content on esa website.
>
> To give you an idea of what I am trying to fix, here is an example input:
>> https://photos.app.goo.gl/o51NfY6aqWn3unPG6
>> This is a 1920x1440 image taken on a GoPro Hero 5 black with the 4:3 Wide
>> FoV setting and stabilisation disabled.
>>
>>
> That is flat take of something else. Not real fisheye input.
>
>
>> The following filtergraph demonstrates the issues:
>> 'v360=input=fisheye:ih_fov=116.66:iv_fov=87.50:output=flat:d_fov=145.8'
>> 1. the dfov_from_hfov issue is worked around by the use of ih_fov and
>> iv_fov instead of id_fov, although you can try with id_fov=145.8 to see
>> that problem too
>> 2. by default the output has double the aspect ratio of the input, even
>> though the fisheye -> rectilinear transformation doesn't change the aspect
>> ratio (assuming the entire input image is included as it is in this example)
>> 3. much of the input is not visible in the output even though there is a
>> mapping between the chosen projections (changed in the visibility test
>> patch)
>>
>> 3 in particular I don't think can be solved by changing the settings -
>> the input field of view needs to match the FoV of the input camera,
>> otherwise the mapping is wrong. But it seems there is no other way to
>> include the entire input from a fisheye image.
>>
>> On Mon, Mar 22, 2021 at 5:59 PM Paul B Mahol <onemda at gmail.com> wrote:
>>
>>>
>>>
>>> On Mon, Mar 22, 2021 at 5:09 AM Daniel Playfair Cal <
>>> daniel.playfair.cal at gmail.com> wrote:
>>>
>>>> I've tried that filtergraph and a few other similar ones and I'm not
>>>> sure what you mean - what exactly is the regression?
>>>>
>>>> I tried it on this image with an equirectangular projection:
>>>> https://wiki.panotools.org/images/0/01/Big_ben_equirectangular.jpg
>>>>
>>>> The only difference I can see is that there are less unmapped areas in
>>>> the output with the patches, because the final mapping from the output
>>>> equirectangular image to the intermediate fisheye image no longer fails to
>>>> map some areas which are present in the fisheye image. I would describe
>>>> this as an improvement?
>>>>
>>>
>>> I disagree, if I use 180 hfov and 180 vfov it should not have extra
>>> areas but only half of previous input.
>>>
>>>
>>>>
>>>> On Mon, Mar 22, 2021 at 3:30 AM Paul B Mahol <onemda at gmail.com> wrote:
>>>>
>>>>> Sorry, but I cannot apply this set as is, It makes at least one
>>>>> serious regression.
>>>>>
>>>>> For example try this filtergraph:
>>>>>
>>>>>
>>>>> v360=input=e:output=fisheye:h_fov=180:v_fov=180,v360=input=fisheye:output=e:ih_fov=180:iv_fov=180
>>>>>
>>>>> On Sun, Mar 21, 2021 at 1:45 PM Daniel Playfair Cal <
>>>>> daniel.playfair.cal at gmail.com> wrote:
>>>>>
>>>>>> This changes the iflat_range and flat_range values for the fisheye
>>>>>> projection to match their meaning for the flat/rectilinear projection.
>>>>>> That is, the range is between the two x or two y coordinates of the
>>>>>> outermost points above/below or left/right of the center, in the
>>>>>> flat/rectilinear projection.
>>>>>>
>>>>>> Signed-off-by: Daniel Playfair Cal <daniel.playfair.cal at gmail.com>
>>>>>> ---
>>>>>> libavfilter/vf_v360.c | 19 +++++++++----------
>>>>>> 1 file changed, 9 insertions(+), 10 deletions(-)
>>>>>>
>>>>>> diff --git a/libavfilter/vf_v360.c b/libavfilter/vf_v360.c
>>>>>> index 68bb2f7b0f..3158451963 100644
>>>>>> --- a/libavfilter/vf_v360.c
>>>>>> +++ b/libavfilter/vf_v360.c
>>>>>> @@ -2807,9 +2807,8 @@ static int prepare_fisheye_out(AVFilterContext
>>>>>> *ctx)
>>>>>> {
>>>>>> V360Context *s = ctx->priv;
>>>>>>
>>>>>> - s->flat_range[0] = s->h_fov / 180.f;
>>>>>> - s->flat_range[1] = s->v_fov / 180.f;
>>>>>> -
>>>>>> + s->flat_range[0] = 0.5f * s->h_fov * M_PI / 180.f;
>>>>>> + s->flat_range[1] = 0.5f * s->v_fov * M_PI / 180.f;
>>>>>> return 0;
>>>>>> }
>>>>>>
>>>>>> @@ -2827,8 +2826,8 @@ static int fisheye_to_xyz(const V360Context *s,
>>>>>> int i, int j, int width, int height,
>>>>>> float *vec)
>>>>>> {
>>>>>> - const float uf = s->flat_range[0] * ((2.f * i) / width - 1.f);
>>>>>> - const float vf = s->flat_range[1] * ((2.f * j + 1.f) / height -
>>>>>> 1.f);
>>>>>> + const float uf = 2.f * s->flat_range[0] / M_PI * ((2.f * i) /
>>>>>> width - 1.f);
>>>>>> + const float vf = 2.f * s->flat_range[1] / M_PI * ((2.f * j +
>>>>>> 1.f) / height - 1.f);
>>>>>>
>>>>>> const float phi = atan2f(vf, uf);
>>>>>> const float theta = M_PI_2 * (1.f - hypotf(uf, vf));
>>>>>> @@ -2858,8 +2857,8 @@ static int prepare_fisheye_in(AVFilterContext
>>>>>> *ctx)
>>>>>> {
>>>>>> V360Context *s = ctx->priv;
>>>>>>
>>>>>> - s->iflat_range[0] = s->ih_fov / 180.f;
>>>>>> - s->iflat_range[1] = s->iv_fov / 180.f;
>>>>>> + s->iflat_range[0] = 0.5f * s->ih_fov * M_PI / 180.f;
>>>>>> + s->iflat_range[1] = 0.5f * s->iv_fov * M_PI / 180.f;
>>>>>>
>>>>>> return 0;
>>>>>> }
>>>>>> @@ -2882,10 +2881,10 @@ static int xyz_to_fisheye(const V360Context
>>>>>> *s,
>>>>>> {
>>>>>> const float h = hypotf(vec[0], vec[1]);
>>>>>> const float lh = h > 0.f ? h : 1.f;
>>>>>> - const float phi = atan2f(h, vec[2]) / M_PI;
>>>>>> + const float phi = atan2f(h, vec[2]);
>>>>>>
>>>>>> - float uf = vec[0] / lh * phi / s->iflat_range[0];
>>>>>> - float vf = vec[1] / lh * phi / s->iflat_range[1];
>>>>>> + float uf = 0.5f * vec[0] / lh * phi / s->iflat_range[0];
>>>>>> + float vf = 0.5f * vec[1] / lh * phi / s->iflat_range[1];
>>>>>>
>>>>>> const int visible = -0.5f < uf && uf < 0.5f && -0.5f < vf && vf
>>>>>> < 0.5f;
>>>>>> int ui, vi;
>>>>>> --
>>>>>> 2.31.0
>>>>>>
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>>>>>
>>>>>
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