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

[Daniel Playfair Cal]

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?

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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