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Update grain.c: grain blending using photographic-paper response. Fixes #11335 #1386

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Merged
merged 4 commits into from
Jan 17, 2017

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arctee
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@arctee arctee commented Dec 15, 2016

A sigmoidal function is used to model a the exposure-density characteristic curve of photographic paper, and the lightness channel is used to modulate the grain accordingly to the characteristic curve. A LUT is used for computational efficiency. The main effect is a fall off of the grain in shadows and highlights accompanied by the skewing of grain distribution (for further info see the discussion on discuss.pixls.us: https://discuss.pixls.us/t/lets-improve-grain/2709/22). A "midtones bias" slider has been added, at 0% the added grain is indistinguishable from the old implementation.

…c curves

A sigmoidal function is used to model a the exposure-density characteristic curve of photographic paper, and the lightness channel is used to modulate the grain accordingly to the characteristic curve. A LUT is used for computational efficiency. The main effect is a fall off of the grain in shadows and highlights accompanied by the skewing of grain distribution (for further info see the discussion on discuss.pixls.us: https://discuss.pixls.us/t/lets-improve-grain/2709/22). A "midtones bias" slider has been added, at 0% the added grain is indistinguishable from the old implementation.
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Looks promising, not too intrusive, but changes are needed.

#define GRAIN_LUT_DELTA_MAX 2.0
#define GRAIN_LUT_DELTA_MIN 0.005
#define GRAIN_LUT_PAPER_GAMMA 1.0

#define CLIP(x) ((x < 0) ? 0.0 : (x > 1.0) ? 1.0 : x)
DT_MODULE_INTROSPECTION(1, dt_iop_grain_params_t)
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Change to

DT_MODULE_INTROSPECTION(2, dt_iop_grain_params_t)

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@arctee arctee Dec 16, 2016

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Thanks for the fast comments to the code. What does DT_MODULE_INTROSPECTION do?

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Most importantly, you changed the size of params struct, so old history stacks, with params struct of old size are now broken.
Bumping version (1->2) at least prevents them from being broken silently.

As for DT_MODULE_INTROSPECTION(), it is just a magic word for introspection generator to create varous functions to be able to generate/modify the params from code easily.

} dt_iop_grain_gui_data_t;

typedef struct dt_iop_grain_data_t
{
_dt_iop_grain_channel_t channel;
float scale;
float strength;
float midtones_bias;
float grain_lut[GRAIN_LUT_SIZE * GRAIN_LUT_SIZE];
} dt_iop_grain_data_t;

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Add:

int legacy_params(dt_iop_module_t *self, const void *const old_params, const int old_version, void *new_params,
                  const int new_version)
{
  if(old_version == 1 && new_version == 2)
  {
    typedef struct dt_iop_grain_params_v1_t
    {
      _dt_iop_grain_channel_t channel;
      float scale;
      float strength;
    } dt_iop_grain_params_v1_t;

    dt_iop_grain_params_v1_t *o = old_params;
    dt_iop_grain_params_t *n = new_params;

    n->channel = o->channel;
    n->scale = o->scale;
    n->strength = o->strength;
    n->midtones_bias = 0.0; // ??? _must_ produce the same results as before this pr

    return 0;
  }
  return 1;
}

@@ -327,6 +335,58 @@ static double _simplex_2d_noise(double x, double y, uint32_t octaves, double per
return total;
}

float paper_resp(float exposure, float mb, float gp)
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static

return density;
}

float paper_resp_inverse(float density, float mb, float gp)
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static

}
}

float dt_lut_lookup_2d_1c(const float *grain_lut, const float x, const float y)
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static


static void evaluate_grain_lut(float * grain_lut, const float mb)
{
for(int i = 0; i < GRAIN_LUT_SIZE; i++)
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maybe

#ifdef _OPENMP
#pragma omp parallel for default(none) collapse(2)
#endif

@@ -423,7 +483,7 @@ void process(struct dt_iop_module_t *self, dt_dev_pixelpipe_iop_t *piece, const
noise = _simplex_2d_noise(x + hash, y, octaves, 1.0, zoom);
}

out[0] = in[0] + ((100.0 * (noise * (strength))) * GRAIN_LIGHTNESS_STRENGTH_SCALE);
out[0] = in[0] + 100 * dt_lut_lookup_2d_1c(data->grain_lut, noise * strength * GRAIN_LIGHTNESS_STRENGTH_SCALE, in[0] / 100);
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100 * dt_lut_lookup_2d_1c(..., in[0] / 100)

Move that 100 into curve, to avoid dividing, and then multiplying

dt_iop_module_t *self = (dt_iop_module_t *)user_data;
if(self->dt->gui->reset) return;
dt_iop_grain_params_t *p = (dt_iop_grain_params_t *)self->params;
p->midtones_bias = dt_bauhaus_slider_get(slider) / 100;
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/ 100
here and everywhere, isn't that an integer division?

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Also, this does not seem nice, it is better to make p->midtones_bias contain the same scale as the slider, and if needed, let the commit_params() do the scaling.

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It is not an integer division. So I should add .0f.
Ok nice, I'll move the scaling of the parameter in commit_params().

@LebedevRI LebedevRI changed the title Update grain.c: grain blending using photographic-paper response Update grain.c: grain blending using photographic-paper response. Fixes #11335 Dec 15, 2016
@@ -496,7 +568,7 @@ void init(dt_iop_module_t *module)
module->params_size = sizeof(dt_iop_grain_params_t);
module->gui_data = NULL;
dt_iop_grain_params_t tmp
= (dt_iop_grain_params_t){ DT_GRAIN_CHANNEL_LIGHTNESS, 1600.0 / GRAIN_SCALE_FACTOR, 25.0 };
= (dt_iop_grain_params_t){ DT_GRAIN_CHANNEL_LIGHTNESS, 1600.0 / GRAIN_SCALE_FACTOR, 25.0, 0.0 };
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I would guess that the new default behavior should be to produce the grain that makes use of this pr.
I.e. that default should not be 0.0.

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It is definitely a good idea.

float paper_resp(float exposure, float mb, float gp)
{
float density;
float delta = GRAIN_LUT_DELTA_MAX * exp(mb * log(GRAIN_LUT_DELTA_MIN));
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$ man 3 log :

LOG(3)                                                                                                                  Linux Programmer's Manual                                                                                                                 LOG(3)

NAME
       log, logf, logl - natural logarithmic function

SYNOPSIS
       #include <math.h>

       double log(double x);

I'm not sure you intended it to actually use double versions

{
float density;
float delta = GRAIN_LUT_DELTA_MAX * exp(mb * log(GRAIN_LUT_DELTA_MIN));
density = (1 + 2 * delta) / (1 + exp( (4 * gp * (0.5 - exposure)) / (1 + 2 * delta) )) - delta;
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All these suffix-less constants seem scary, too easy to unintentionally do int-based operation i'd say.
Append .0f

float paper_resp_inverse(float density, float mb, float gp)
{
float exposure;
float delta = GRAIN_LUT_DELTA_MAX * exp(mb * log(GRAIN_LUT_DELTA_MIN));
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Same as for paper_resp()

@LebedevRI LebedevRI added the feature: enhancement current features to improve label Dec 15, 2016
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Seems to be going in the right direction.

static float paper_resp(float exposure, float mb, float gp)
{
float density;
float delta = GRAIN_LUT_DELTA_MAX * exp(mb * logf(GRAIN_LUT_DELTA_MIN));
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Same applies to exp(), it should probably be expf()

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I wonder if it's worth to use dt_fast_expf() everywhere?

static float paper_resp_inverse(float density, float mb, float gp)
{
float exposure;
float delta = GRAIN_LUT_DELTA_MAX * exp(mb * logf(GRAIN_LUT_DELTA_MIN));
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Same applies to exp(), it should probably be expf()

@@ -530,6 +628,14 @@ void gui_init(struct dt_iop_module_t *self)
gtk_box_pack_start(GTK_BOX(self->widget), GTK_WIDGET(g->scale2), TRUE, TRUE, 0);
gtk_widget_set_tooltip_text(g->scale2, _("the strength of applied grain"));
g_signal_connect(G_OBJECT(g->scale2), "value-changed", G_CALLBACK(strength_callback), self);

/* midtones bias */
g->scale3 = dt_bauhaus_slider_new_with_range(self, 0.0, 100.0, 1.0, p->midtones_bias * 100, 2);
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Hm, or you could make that slider have 0..1 range.
I'm not sure whether it is better or worse than percents though.

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The current strength slider is in percent, so this one should behave the same.

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Makes sense.

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Makes sense to me, also.

static float paper_resp(float exposure, float mb, float gp)
{
float density;
float delta = GRAIN_LUT_DELTA_MAX * exp(mb * logf(GRAIN_LUT_DELTA_MIN));
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I wonder if it's worth to use dt_fast_expf() everywhere?

@@ -423,7 +509,7 @@ void process(struct dt_iop_module_t *self, dt_dev_pixelpipe_iop_t *piece, const
noise = _simplex_2d_noise(x + hash, y, octaves, 1.0, zoom);
}

out[0] = in[0] + ((100.0 * (noise * (strength))) * GRAIN_LIGHTNESS_STRENGTH_SCALE);
out[0] = in[0] + (100.0 * dt_lut_lookup_2d_1c(data->grain_lut, (noise * strength) * GRAIN_LIGHTNESS_STRENGTH_SCALE, in[0] / 100.0));
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Why don't you push the 100.0 * into the LUT? It's not much, but would save a few cycles. Or would that give different results? I haven't really tried to understand the logic yet.

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Yes, no problem, it can be moved into the LUT.

dt_iop_module_t *self = (dt_iop_module_t *)user_data;
if(self->dt->gui->reset) return;
dt_iop_grain_params_t *p = (dt_iop_grain_params_t *)self->params;
p->midtones_bias = dt_bauhaus_slider_get(slider);
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The other GUI callbacks do the scaling of the slider values here already.

@@ -462,6 +556,9 @@ void commit_params(struct dt_iop_module_t *self, dt_iop_params_t *p1, dt_dev_pix
d->channel = p->channel;
d->scale = p->scale;
d->strength = p->strength;
d->midtones_bias = p->midtones_bias / 100.0f;
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Instead of scaling here you should do it in midtones_bias_callback().

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No.
What about introspection?

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What about it? The rest of that IOP scales in the other place already.

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@LebedevRI LebedevRI Dec 17, 2016

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If for consistency with the old code in this IOP, then yes, probably better to handle it in callbacks.
But i think in new code it should be done in commit_params() if needed at all.

Edit: because displaying parameter with one range (0..100%) in gui, and with another rande in params and introspection (0..1) will probably be confusing for someone who tries to use introspection.

@@ -530,6 +628,14 @@ void gui_init(struct dt_iop_module_t *self)
gtk_box_pack_start(GTK_BOX(self->widget), GTK_WIDGET(g->scale2), TRUE, TRUE, 0);
gtk_widget_set_tooltip_text(g->scale2, _("the strength of applied grain"));
g_signal_connect(G_OBJECT(g->scale2), "value-changed", G_CALLBACK(strength_callback), self);

/* midtones bias */
g->scale3 = dt_bauhaus_slider_new_with_range(self, 0.0, 100.0, 1.0, p->midtones_bias * 100, 2);
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The current strength slider is in percent, so this one should behave the same.

dt_bauhaus_widget_set_label(g->scale3, NULL, _("midtones bias"));
dt_bauhaus_slider_set_format(g->scale3, "%.0f%%");
gtk_box_pack_start(GTK_BOX(self->widget), GTK_WIDGET(g->scale3), TRUE, TRUE, 0);
gtk_widget_set_tooltip_text(g->scale3, _("amount of midtones bias from the photographic paper response modeling"));
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Maybe add a sentence about what low/high values do. Not critical, but who reads the manual … 😄

I moved the scaling of midtone_bias into the LUT functions, now the parameter is always a percentage. I added also `dt_fast_expf()`.
@TurboGit TurboGit added the incomplete pull request needing changes to be merged label Jan 2, 2017
I noticed some luminance shifting using `dt_fast_expf()`, changing back to `expf()`.
@arctee
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arctee commented Jan 16, 2017

What remains to be done in your opinion?

@houz
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houz commented Jan 16, 2017

I didn't try it yet, but the code looks ok to me.

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I've tested it but I cannot see a difference when using the midtone-bias slider. I've looked at the image closely in different location. It seems that the image is not changed. The histogram moves a bit, so I suppose that there is some changes done to the image. Where should I looked? How this slider is working? Thanks.

@houz
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houz commented Jan 17, 2017

Look in black and white parts of the image. The grain should get less there.

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Indeed! Thanks Tobias now I see it. Not a strong effect but nice.

@TurboGit TurboGit removed the incomplete pull request needing changes to be merged label Jan 17, 2017
@LebedevRI LebedevRI dismissed their stale review January 17, 2017 16:10

All my notes were addressed.

@houz houz merged commit f52fe5c into darktable-org:master Jan 17, 2017
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houz commented Jan 17, 2017

Thank you, I like the result much more than the old grain.

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arctee commented Jan 17, 2017

Thank you all for helping and reviewing the code.

@LebedevRI LebedevRI modified the milestone: 2.4 Jan 21, 2017
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4 participants