A lens correction the camera maker measured and wrote into the file, as knots. More...

#include <lensserious.h>

Collaboration diagram for ls_knots_t:

Data Fields
int	n

float	radius [16]

float	cor_rgb [3][16]

int	vn

float	vig_radius [16]

float	vig [16]

Detailed Description

A lens correction the camera maker measured and wrote into the file, as knots.

The second source of correction data this library resolves, beside the lens database. Most mirrorless makers – Sony, Fujifilm, Olympus, and anyone writing DNG 1.3 opcodes – embed a profile of the lens that took the picture in its metadata, and they all express it the same way: a short list of radii and, at each, the factor the coordinate should be scaled by. Not a model with coefficients; the samples themselves, meant to be read back with straight-line interpolation between them.

Two things about the shape of it matter to everything downstream:

It is per CHANNEL. cor_rgb holds red, green and blue separately, so distortion and lateral chromatic aberration arrive measured together rather than as a geometry plus a correction on top of it. There is no TCA stage to run afterwards.
It is measured on the lens as shipped. There is no projection to change and no calibration sensor to convert from, which is why this needs none of the arguments ls_modifier_init() takes: no crop factor, no aperture, no subject distance, and no focal, because the maker already resolved the profile at the focal that was used.

radius, and vig_radius with it, are the distance from the IMAGE CENTRE over half the image diagonal – 1.0 at the far corner. That is the makers' own convention and this library adopts it wholesale rather than converting, so the numbers a decoder lifts out of the file go in unmodified.

Definition at line 162 of file lensserious.h.

Field Documentation

◆ cor_rgb

float ls_knots_t::cor_rgb[3][16]

At each radius, source_radius / this_radius, per channel: 0 red, 1 green, 2 blue. The direction is the CORRECTING one – given a point in the corrected image, where in the source image it came from – which is what the makers publish and what a resampler consumes. Ask ls_modifier_init_knots() for the other one and it inverts the table.

Definition at line 172 of file lensserious.h.

Referenced by _dng_populate(), _fuji_populate(), _olympus_populate(), _sony_populate(), ls_modifier_init_knots(), and ls_vendor_resolve().

◆ n

int ls_knots_t::n

How many distortion/TCA knots, up to LS_MAX_KNOTS. Zero for none.

Definition at line 165 of file lensserious.h.

Referenced by ls_modifier_init_knots(), and ls_vendor_resolve().

◆ radius

float ls_knots_t::radius[16]

Ascending radii, n of them, shared by all three channels.

Definition at line 167 of file lensserious.h.

Referenced by _dng_populate(), _fuji_populate(), _olympus_populate(), _sony_populate(), ls_modifier_init_knots(), and ls_vendor_resolve().

◆ vig

float ls_knots_t::vig[16]

The falloff itself, as the maker measured it: below 1 where the lens darkens. A pixel is CORRECTED by dividing by it, which is upstream lensfun's convention too.

Definition at line 180 of file lensserious.h.

Referenced by _dng_populate(), _fuji_populate(), _olympus_populate(), _sony_populate(), and ls_modifier_init_knots().