Issue #108: Add accessibility options in pdf reader

Pdf4QtLib/sources/pdfcolorconvertor.h

@@ -0,0 +1,139 @@
+//    Copyright (C) 2023 Jakub Melka
+//
+//    This file is part of PDF4QT.
+//
+//    PDF4QT is free software: you can redistribute it and/or modify
+//    it under the terms of the GNU Lesser General Public License as published by
+//    the Free Software Foundation, either version 3 of the License, or
+//    with the written consent of the copyright owner, any later version.
+//
+//    PDF4QT is distributed in the hope that it will be useful,
+//    but WITHOUT ANY WARRANTY; without even the implied warranty of
+//    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+//    GNU Lesser General Public License for more details.
+//
+//    You should have received a copy of the GNU Lesser General Public License
+//    along with PDF4QT.  If not, see <https://www.gnu.org/licenses/>.
+
+#ifndef PDFCOLORCONVERTOR_H
+#define PDFCOLORCONVERTOR_H
+
+#include "pdfglobal.h"
+
+#include <QColor>
+#include <QImage>
+
+namespace pdf
+{
+
+/// \class PDFColorConvertor
+/// \brief Performs color conversions in the RGB color space.
+/// This class supports multiple modes of operation, making it
+/// useful for accessibility purposes, particularly for visually impaired users.
+class PDF4QTLIBSHARED_EXPORT PDFColorConvertor
+{
+public:
+    PDFColorConvertor();
+
+    /// Enumeration for different modes of color conversion
+    enum class Mode
+    {
+        Normal,             ///< No color conversion is performed.
+        InvertedColors,     ///< Inverts colors in the RGB space.
+        Grayscale,          ///< Converts colors to grayscale.
+        HighContrast,       ///< Adjusts contrast using a sigmoid function.
+        Bitonal,            ///< Creates a monochromatic (two-color) image.
+        CustomColors,       ///< Applies custom foreground and background colors.
+   };
+
+    bool operator==(const PDFColorConvertor&) const = default;
+    bool operator!=(const PDFColorConvertor&) const = default;
+
+    /// Checks if color conversion is active.
+    /// \return `true` if color conversion is currently active; `false` otherwise.
+    /// When `false`, no color conversions are performed, and the `convert` function
+    /// operates as an identity function.
+    bool isActive() const;
+
+    /// Sets the mode for color conversion.
+    /// \param mode Specifies the new mode to be used for color conversion.
+    /// This mode determines how colors are transformed during the conversion process.
+    void setMode(Mode mode);
+
+    /// Converts the given color based on the current mode
+    /// \param color The QColor to be converted
+    /// \param background Use background color
+    /// \param foreground Use foreground color
+    /// \return The converted QColor
+    QColor convert(QColor color, bool background, bool foreground) const;
+
+    /// Converts the given image based on the current mode
+    /// \param image The image to be converted
+    /// \return The converted image
+    QImage convert(QImage image) const;
+
+    /// Sets the correction factor for enhancing contrast in high contrast mode.
+    /// This factor determines the level of contrast enhancement:
+    /// - For subtle enhancement, set the factor between 5 and 10.
+    /// - For moderate enhancement, use values between 10 and 20.
+    /// - For strong enhancement, choose values of 20 or higher.
+    /// \param factor The correction factor used for adjusting contrast.
+    void setHighContrastBrightnessFactor(float factor);
+
+    /// Retrieves the current bitonal threshold value used for determining lightness levels.
+    /// This threshold helps in differentiating between light and dark areas in an image processing context.
+    /// \returns The current bitonal threshold value as an integer. This value is used to classify pixels
+    /// as either light or dark based on their lightness.
+    int getBitonalThreshold() const;
+
+    /// Sets a new bitonal threshold value to be used in image processing.
+    /// This threshold determines how lightness levels are classified into binary categories (light or dark).
+    /// \param newBitonalThreshold The new threshold value as an integer. It should be chosen carefully
+    /// to ensure accurate differentiation between light and dark areas in images.
+    void setBitonalThreshold(int newBitonalThreshold);
+
+private:
+    /// Correct lightness using sigmoid function
+    /// \return Adjusted lightness normalized in range [0.0, 1.0]
+    /// \param lightness Lightness in range [0.0, 1.0]
+    float correctLigthnessBySigmoidFunction(float lightness) const;
+
+    /// Calculates the value of the sigmoid function based on the given input.
+    /// The returned value is unscaled and should be scaled to the range [0.0, 1.0]
+    /// using other functions.
+    /// \param value The input value for the sigmoid function.
+    /// \return The unscaled result of the sigmoid function.
+    float sigmoidFunction(float value) const;
+
+    /// Determines the sigmoid function value for a completely black color
+    /// (i.e., when lightness is set to zero).
+    /// \return The sigmoid function value corresponding to black color.
+    float sigmoidParamC_Black() const;
+
+    /// Determines the sigmoid function value for a completely white color
+    /// (i.e., when lightness is set to one).
+    /// \return The sigmoid function value corresponding to white color.
+    float sigmoidParamC_White() const;
+
+    /// Determines the range of the sigmoid function's output,
+    /// useful for scaling the range to the normalized interval [0.0, 1.0].
+    /// \return The range of the sigmoid function's output.
+    float sigmoidParamC_Range() const;
+
+    /// Calculates parameters for the sigmoid function,
+    /// which are used to scale color values to the interval [0.0, 1.0].
+    void calculateSigmoidParams();
+
+    Mode m_mode = Mode::Normal;
+    float m_sigmoidParamC = 10.0f;
+    float m_sigmoidParamC_Black = 0.0f;
+    float m_sigmoidParamC_White = 1.0f;
+    float m_sigmoidParamC_Range = 1.0f;
+    int m_bitonalThreshold = 128;
+    QColor m_backgroundColor = Qt::black;
+    QColor m_foregroundColor = Qt::green;
+};
+
+}   // namespace pdf
+
+#endif // PDFCOLORCONVERTOR_H