[FFmpeg-devel] [PATCH 4/4] avfilter/vf_v360: refactor (i)flat_range for fisheye

[Paul B Mahol]

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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>>
>>