[FFmpeg-devel] [PATCH 4/4] avfilter/vf_v360: refactor (i)flat_range for fisheye
Paul B Mahol
onemda at gmail.com
Tue Mar 23 08:14:49 EET 2021
On Tue, Mar 23, 2021 at 5:00 AM Daniel Playfair Cal <
daniel.playfair.cal at gmail.com> wrote:
> What exactly is your definition of fisheye?
>
Take look at source code. I do not see how your definition matches one in
source code.
>
> 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
>>>>>>>
>>>>>>> _______________________________________________
>>>>>>> ffmpeg-devel mailing list
>>>>>>> ffmpeg-devel at ffmpeg.org
>>>>>>> https://ffmpeg.org/mailman/listinfo/ffmpeg-devel
>>>>>>>
>>>>>>> To unsubscribe, visit link above, or email
>>>>>>> ffmpeg-devel-request at ffmpeg.org with subject "unsubscribe".
>>>>>>
>>>>>>
More information about the ffmpeg-devel
mailing list