A simple C++ project for applying filters to raw images via command line. http://www.albertodebortoli.it

https://github.com/albertodebortoli/ImageAnalysisFilters

Image Analysis Filters

A simple C++ project for applying filters to raw images via command line.

Author: Alberto De Bortoli
Date: august 2008
Course: Elaborazione delle Immagini (Image Analysis) Università degli studi di Padova, Prof. Paolo Cattani
Website: albertodebortoli.it

Compile the project with 'make' command with g++ (tested on version 4.2.1). Executable file 'ImageFilters' is generated for your architecture.

Description and usage

Source code files in the project:

• Main.cpp
• Image.{h,cpp}
• FiltersPunctual.{h,cpp}
• FiltersConvolution.{h,cpp}
• FiltersAdj.{h,cpp}
• FiltersStripes.{h,cpp}
• FT.{h,cpp}
• FFT.{h,cpp}

The project implement the following:

• Custom image size;
• FT and FFT for high or low pass filter with cutoff value;
• Implemented filters: Brightness, Auto Contrast, Gamma Correction, Gamma Correction on channels, Invert, Mirror, Pixelazer, Smooth, Noise Removal, Blur, Outliner (Emboss), Sharpen, Rotation;
• Low pass filter without using FT.

Execution needs at least 7 command line arguments. 6 base arguments and 1 for the chosen filter to apply to the source image. First 6 base arguments are described as follow:

1. path source image (*.raw)
2. path immagine destinazione (*.raw)
3. source image width
4. source image height
5. kind of source image ('0' for grayscale, '1' for color RGB interleaved)
6. kind of destination image ('0' for grayscale, '1' for color RGB interleaved)

Here is an example of usage with the first 6 arguments:

./ImageFilters ./img/400x300RGB.raw ./img/output.raw 400 300 1 0

One more argument (at least) is needed for filter application. Filters can be applied sequentially. Filters description follows.

Equalize

Spread the hystogram of gray over all the range of color space.
syntax: e
example: e

Brightness

Modify the image brightness using a given value.
syntax: l <mod_value>
example: l 2.0

Automatic Contrast

Apply auto contrast filter. Spread the hystogram to use the entire range.
syntax: a
example: a

Gamma Correction

Apply Gamma Correction filter with a given value.
syntax: g <mod_value>
example: g 0.8

Channel

Apply Gamma Correction filter on a given RGB channel with a given value. Only applicable to color images.
syntax: h <mod_value> <channel>
example: h 0.8 R

Invert

Invert the colors in the image.
syntax: i
example: i

Mirror

Mirror the image. If <mod_value> is the direction ('X' for horizontally, 'Y' for vertically).
syntax: m <mod_value>
example: m X

Pixelizer

Apply the pixelize filter. <mod_value> is the size of the macro pixel in the output image.
syntax: p <mod_value>
example: p 6

Smooth

Apply smooth effect using a <kernel_dim>x<kernel_dim> kernel matrix.
syntax: s <kernel_dim>
example: s 5

Remove noise

Remove the noise using a <kernel_dim>x<kernel_dim> kernel matrix.
syntax: r <kernel_dim>
example: r 5

Sharpen - Blur - Outline

Apply a convolution filter using a 3x3 kernel matrix.< filter_type> can be:
'S' for Sharpen filter
'B' for Blur filter
'O' for Outliner (emboss filter)
syntax: c <filter_type>
example: c S

Rotation

Rotate the image of degrees.
syntax: q <rotation_angle>
example: q 45

Zoom

Zoom in or out. <zoom_flag> can be '-' for zoom in or '+' for zoom out. <mod_value> is the zoom percentage.
syntax: z <zoom_flag> <mod_value>
example: z + 30

Resize

Resize the image. Output image has width, height is proportionally derived. syntax: Z <mod_value>
example: Z 250

Grayscale

Convert a color image (RGB) to grayscale. Only applicable to grayscale images.
syntax: b
example: b

Low-Pass filter

Cuts off high frequencies. <cutoff_value> (the cut off value) and <kernel_dim> (the kernel dimension) result in a stronger or weaker filter effect.
syntax: - <cutoff_value> <kernel_dim>
example: - 15 5

Fourier Transform

Two kind of Fourier Transform can be used: FT and FFT. They are used for frequency filtering (low-pass/high-pass filter). Classic FT runs in N^2, FFT runs in N log N.

syntax: <FT_type> <filter_type> <cutoff_value> <filtering_type>
example: f l 30 I

<FT_type> is for FT ('f') or for FFT ('F').
< filter_type> can be 'l' o 'h' based on low or high filter application.
< cutoff_value> is the cutoff value.
< filtering_type> is for ideal filtering (ILPF/IHPF) ('I') or bell shaped 'B' one.

Application of filter automatically saves spectrum in ‘magnitude.raw’ file for later access.

Here are example of usage of FT. Source image is 128x128 grayscale.

Original image

Transform spectrum

Here are the spectrums and the image as result of filter application.
Low-pass filter, ideal, threshold = 30
syntax: ./ImageFilters ./img/128x128BN.raw ./img/output.raw 128 128 0 0 F l 30 I

Low-pass filter, bell shaped, threshold = 30
syntax: ./ImageFilters ./img/128x128BN.raw ./img/output.raw 128 128 0 0 F l 30 C

High-pass filter, ideal, threshold = 10
syntax: ./ImageFilters ./img/128x128BN.raw ./img/output.raw 128 128 0 0 F h 10 I

High-pass filter, ideal, threshold = 10
syntax: ./ImageFilters ./img/128x128BN.raw ./img/output.raw 128 128 0 0 F h 10 C

Source images need to be power of 2 size to apply FFT. If not, scaling to next power of 2 is applied filling empty spaces with 0 (black). The image is then trimmed back to original size fter FFT.

Source image 160x100

Scaled image to power of 2 size, i.e 256x128

Scaled image spectrum

Image after backward FFT

Cut image to original size 160x100

Following images show the differences between hystogram equalization of pre and post equalization.

Pre filtering equalization

Post filtering equalization

License

Licensed under the New BSD License.

Copyright (c) 2008, Alberto De Bortoli at Università degli Studi di Padova. All rights reserved.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: * Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. * Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution. * Neither the name of the Università degli Studi di Padova nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY Alberto De Bortoli ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL Alberto De Bortoli BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.