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While doing this, I could find a lot of problems in the algorithm: 1. It looks like the original intent (from GUI and code) is that you set hue and saturation but not really the intended lightness, rather its increase or decrease, relatively to every pixel current lightness. I.e. that every pixel will be set to the selected hue and saturation, and only the lightness will change. The "lightness" field is therefore a relative value (pixel per pixel). The first problem is that instead of lightness, we compute the luminance, which is related but different and set this in the lightness field. 2. The second issue is that we were using gimp_hsl_to_rgb() which after testing (because its documentation doesn't give any TRC/space info at all) looks like it computes a color from HSL to non-linear RGB of the same space. Yet we were outputting to a linear RGB space. So we compute the wrong values. On the other hand, because of the first problem, I realize (after testing) that it makes our render closer to the intended render by chance (at least when the TRC is sRGB's). It's still wrong, but if we were to change the output to "R'G'B'A float" instead, the render would be much darker. In both cases, it's wrong anyway. I would not say that the 2 problems are canceling each others, but they are making the final result somewhat OK. 3. Ideally we should be using babl to convert colors, and this is the best way to actually implement the original filter intent. Unfortunately so far, doing this is much slower (though I save a lot of time by moving out of the samples loop and processing data in chunks, it's still slower than the current, nearly instant, implementation). 4. Because of all previous implementation irregularities, the render is different depending on the actual image space. I.e. that the exact same image filtered through Colorize with the exact same operation parameters will render differently. I would need to test further, and maybe it's normal since HSL is also space-dependant (and that's where we work on in this operation), but I'm wondering if the result should not be independant of the working space. 5. I implemented our own prepare() method because the one in GimpOperationPointFilter parent seems to allow other input or output models. Even though in all my tests, it was always linear RGB (which is what we want here), let's make sure by having a custom prepare() method explicitly setting these. It's also the opportunity to create some babl fishes. In any case, I'm leaving the code as-is for now, because it's how this operation has been since forever (at least for as long as I was around) and I don't think it's the right idea to change it on a whim. This raises even more the concern of versionning GEGL operation, which we have been discussing with pippin on IRC lately, because if ever we want to change this one, now that operations are not just applied, but possibly non-destructively recreated at load, we need to make sure that we recreate the render expected at the time of creation of a XCF while allowing us to have the filters improving when needed.
60 lines
2.3 KiB
C
60 lines
2.3 KiB
C
/* GIMP - The GNU Image Manipulation Program
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* Copyright (C) 1995 Spencer Kimball and Peter Mattis
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*
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* gimpoperationcolorize.h
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* Copyright (C) 2007 Michael Natterer <mitch@gimp.org>
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*
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* This program is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 3 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program. If not, see <https://www.gnu.org/licenses/>.
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*/
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#ifndef __GIMP_OPERATION_COLORIZE_H__
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#define __GIMP_OPERATION_COLORIZE_H__
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#include "gimpoperationpointfilter.h"
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#define GIMP_TYPE_OPERATION_COLORIZE (gimp_operation_colorize_get_type ())
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#define GIMP_OPERATION_COLORIZE(obj) (G_TYPE_CHECK_INSTANCE_CAST ((obj), GIMP_TYPE_OPERATION_COLORIZE, GimpOperationColorize))
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#define GIMP_OPERATION_COLORIZE_CLASS(klass) (G_TYPE_CHECK_CLASS_CAST ((klass), GIMP_TYPE_OPERATION_COLORIZE, GimpOperationColorizeClass))
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#define GIMP_IS_OPERATION_COLORIZE(obj) (G_TYPE_CHECK_INSTANCE_TYPE ((obj), GIMP_TYPE_OPERATION_COLORIZE))
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#define GIMP_IS_OPERATION_COLORIZE_CLASS(klass) (G_TYPE_CHECK_CLASS_TYPE ((klass), GIMP_TYPE_OPERATION_COLORIZE))
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#define GIMP_OPERATION_COLORIZE_GET_CLASS(obj) (G_TYPE_INSTANCE_GET_CLASS ((obj), GIMP_TYPE_OPERATION_COLORIZE, GimpOperationColorizeClass))
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typedef struct _GimpOperationColorize GimpOperationColorize;
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typedef struct _GimpOperationColorizeClass GimpOperationColorizeClass;
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struct _GimpOperationColorize
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{
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GimpOperationPointFilter parent_instance;
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gfloat hue;
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gfloat saturation;
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gfloat lightness;
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const Babl *hsl_format;
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const Babl *fish_to_lum;
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const Babl *fish_from_hsl;
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};
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struct _GimpOperationColorizeClass
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{
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GimpOperationPointFilterClass parent_class;
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};
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GType gimp_operation_colorize_get_type (void) G_GNUC_CONST;
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#endif /* __GIMP_OPERATION_COLORIZE_H__ */
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