[FFmpeg-devel] [PATCH 1/2] avfilter/vf_gblur: fix divide by zero

[zhilizhao]

> On Jan 4, 2020, at 7:04 PM, Paul B Mahol <onemda at gmail.com> wrote:
> 
> I do not like this “fix"

What do you suggest?  It’s numerical unstable for small sigma.

> 
> On 1/4/20, quinkblack at foxmail.com <quinkblack at foxmail.com> wrote:
>> From: Zhao Zhili <zhilizhao at tencent.com>
>> 
>> ./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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