FFmpeg
[WIP] Multispectral support
This is not to merge yet, but for discussion and of course if anyone wants to contribute/add to it
On my side, I made good experiences definitying the wavelength (in nm) for each spectral band.
On my side, I made good experiences definitying the wavelength (in nm) for each spectral band.
I used hz in the hope that the whole relevant EM spectrum could be represented and as its a fundamental unit. (quite possibly ive missed something of course). with nm we would need fractional values and not just integers if we wanted to store X-ray images and use this field to hold some acccurate X-ray frequency information
I’m afraid, I’m probably missing something! It seems to me that the integers vs. fractions issue is the same when expressed in Hz or in m, which are actually both SI base units. (Context: I made that choice, because it’s the information characterising the filters we use… Anyway, the conversion between them is elementary.)
If one wanted to use integers to handle the value, with Hz that works for most of the relevant spectrum with also very good precision for the range one is able to make pictures with. visual, UV, ir, xrays are all high frequency so lots of digits precission. With really long radio waves making images will be very hard as the antenna has to scale up size wise. OTOH with meters as the base unit most of the relevant spectrum falls below 1.0 so fractional numbers need to be handled. Also with wavelength we would need to clarify if that is wavelength in air, in vacuum or in the medium the picture was taken. But ultimately it of course makes no real difference either way can be used to store the value. In practice maybe we should use a mantisse * 2^exponent style storage as fractions as in a/b would result in values for either a or b not fitting in 64bit integers. Ill try to come up with some better suggestion in a future patch revission
Just out of curiosity: is there any work going on here? (I will be in Vienna from Thursday to Sunday and could meet if useful. Then again the week 6–10 January.)
I was at a pronom workshop recently and there were some Dicom images. Perhaps pronom have these images available as part of a test suite?
On Tue 25 Oct 2022 at 23:31, Michael Niedermayer @.***> wrote:
@.**** commented on this pull request.
In ffv1.md https://github.com/FFmpeg/FFV1/pull/138#discussion_r1004982100:
+| 4 | Retro-Reflective | +| 5 | Mask | +| 6 | Depth | +| 7 | Motion | +| 8 | Error | +| 9 | Force Field | +| 10 | Polarization | +| 11-999 | Reserved |
+### per_plane_metadata_count + +
per_plane_metadata_countallows future extension of the information we store about planes + +### center_frequency + +center_frequencyindicates the center frequency in hz. Or 0 if unknown or not applicable.If you need samples there should be lots of public stuff from astronomy and satellites. For xrays and MRT the word to search for is probably dicom image. One source for public domain samples would be any images you own the rights to, like from a medical exam. I didnt really try to find free proper raw sample images for these things previously ...
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