tiff/geotiff support : number precision is not sufficient in double to string conversion

[LeRatier]

In libavcodec/tiff.c, the double values of the GEOTIFF format are converted to string thru the double2str() function.

This function is truncating double to 6 digits (ie the printf("%f") default), leading to critical precision loss when using the result on the decoder side

An easy patch would be to modify the "%f%s" of the snprintf in a "%.15g%s" for example.

[Carl Eugen Hoyos]

If you want to report an issue here, please provide a sample and complete, uncut ffmpeg -i output for the sample.
If you already have a fix for the issue, please send a patch made with git format-patch to the ffmpeg-devel mailing list.

[LeRatier]

Patch creation in progress.
By the way, same issue in int ff_tadd_doubles_metadata(int count, const char *name, const char *sep,

GetByteContext *gb, int le, AVDictionary metadata)

the %f is not sufficient to retrieve the real precision of the input numbers.

[Carl Eugen Hoyos]

Your patch was committed, could you add a sample that allows to reproduce the problem you had?

[LeRatier]

The source picture i am working on are confidential, so i cannot add them directly as samples. Anyway, i think it is a global issue, maybe present in other double metadatas : as soon as you convert a double value to a string, you should use something like %.15g instead of the default %f, that truncate the number at 6 digits.