> On Jan 4, 2020, at 9:43 PM, zhilizhao <[email protected]> wrote:
>
>
>
>> On Jan 4, 2020, at 9:09 PM, Paul B Mahol <[email protected]
>> <mailto:[email protected]>> wrote:
>>
>> On 1/4/20, zhilizhao <[email protected]
>> <mailto:[email protected]>> wrote:
>>>
>>>
>>>> On Jan 4, 2020, at 7:04 PM, Paul B Mahol <[email protected]
>>>> <mailto:[email protected]>> wrote:
>>>>
>>>> I do not like this “fix"
>>>
>>> What do you suggest? It’s numerical unstable for small sigma.
>>
>> For small sigma return frames unchanged as it currently does.
>
> Then which valud should be selected as the threshold:
>
> 1. A value from which it becomes unstable (it’s not fun to figure it out).
>
> 2. A reasonable (and random) selected value like 0.25
>
For function set_params:
static void set_params(float sigma, int steps, float *postscale, float
*boundaryscale, float *nu)
{
double dnu, lambda;
lambda = (sigma * sigma) / (2.0 * steps);
dnu = (1.0 + 2.0 * lambda - sqrt(1.0 + 4.0 * lambda)) / (2.0 * lambda);
*postscale = pow(dnu / lambda, steps);
*boundaryscale = 1.0 / (1.0 - dnu);
*nu = (float)dnu;
}
1. Check sigma against 0 is not enough, since lambda can be 0 for non-zero sigma
2. Check lambda against 0 is not enough, we should avoid dividing by small
value, like 'dnu / lambda’.
So there should have a dead-zone for sigma.
>
>>
>>>
>>>>
>>>> On 1/4/20, [email protected] <[email protected]> wrote:
>>>>> From: Zhao Zhili <[email protected]>
>>>>>
>>>>> ./ffmpeg -i ~/Pictures/test.jpg -vf 'gblur=sigma=0' -f null -
>>>>> ...
>>>>> src/libavfilter/vf_gblur.c:260:59: runtime error: division by zero
>>>>> src/libavfilter/vf_gblur.c:261:26: runtime error: division by zero
>>>>> ---
>>>>> libavfilter/vf_gblur.c | 12 +++++++++---
>>>>> 1 file changed, 9 insertions(+), 3 deletions(-)
>>>>>
>>>>> diff --git a/libavfilter/vf_gblur.c b/libavfilter/vf_gblur.c
>>>>> index 2e587f6a0a..e057937fb7 100644
>>>>> --- a/libavfilter/vf_gblur.c
>>>>> +++ b/libavfilter/vf_gblur.c
>>>>> @@ -37,11 +37,17 @@
>>>>> #define OFFSET(x) offsetof(GBlurContext, x)
>>>>> #define FLAGS
>>>>> AV_OPT_FLAG_VIDEO_PARAM|AV_OPT_FLAG_FILTERING_PARAM|AV_OPT_FLAG_RUNTIME_PARAM
>>>>>
>>>>> +/* Consider the three-sigma rule, for minimum radius of 1 sigma should
>>>>> not
>>>>> + * be smaller than 1/3. Relax it to 0.25 if the user want to try.
>>>>> + */
>>>>> +#define SIGMA_MIN 0.25
>>>>> +#define SIGMA_MAX 1024.0
>>>>> +
>>>>> static const AVOption gblur_options[] = {
>>>>> - { "sigma", "set sigma", OFFSET(sigma),
>>>>> AV_OPT_TYPE_FLOAT,
>>>>> {.dbl=0.5}, 0.0, 1024, FLAGS },
>>>>> + { "sigma", "set sigma", OFFSET(sigma),
>>>>> AV_OPT_TYPE_FLOAT,
>>>>> {.dbl=0.5}, SIGMA_MIN, SIGMA_MAX, FLAGS },
>>>>> { "steps", "set number of steps", OFFSET(steps), AV_OPT_TYPE_INT,
>>>>> {.i64=1}, 1, 6, FLAGS },
>>>>> { "planes", "set planes to filter", OFFSET(planes), AV_OPT_TYPE_INT,
>>>>> {.i64=0xF}, 0, 0xF, FLAGS },
>>>>> - { "sigmaV", "set vertical sigma", OFFSET(sigmaV),
>>>>> AV_OPT_TYPE_FLOAT,
>>>>> {.dbl=-1}, -1, 1024, FLAGS },
>>>>> + { "sigmaV", "set vertical sigma", OFFSET(sigmaV),
>>>>> AV_OPT_TYPE_FLOAT,
>>>>> {.dbl=-1}, -1, SIGMA_MAX, FLAGS },
>>>>> { NULL }
>>>>> };
>>>>>
>>>>> @@ -244,7 +250,7 @@ static int config_input(AVFilterLink *inlink)
>>>>> if (!s->buffer)
>>>>> return AVERROR(ENOMEM);
>>>>>
>>>>> - if (s->sigmaV < 0) {
>>>>> + if (s->sigmaV < SIGMA_MIN) {
>>>>> s->sigmaV = s->sigma;
>>>>> }
>>>>> ff_gblur_init(s);
>>>>> --
>>>>> 2.22.0
>>>>>
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>>>
>>>
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