## Copyright Mantu Matei 312CA 2022-2023
# README tema03: Image Editor

## Description
This program written in C loads Portable GrayMap (PGM) and Portable
PixMap (PPM) files and can select portions of the photos, rotate, crop,
equalize, apply filters, print a histogram and save the results in
either an ascii format or a binary format.

## Usage + How it works
For making this program, I have made an `image` struct that contains
the size of the image along the coordinates of the points that define
the selected portion of the picture, the type of the image and the max
value of the pixels.

At first, the program awaits a Netpbm format picture to be loaded from
locat files. It is done by using the command `LOAD <filename>`.
Then, several comands can be executed:

1. `LOAD <filename>` - deletes the previously loaded picture and loads a
new one from `<filename>`. If the picture is saved in binary form, it is
read byte by byte using an `unsigned char` variable (because unsigned char
has a range of 0-255 - exactly the range of one byte). All lines containing `#`
in the file are ignored as they are considered to be comments.

2. `SELECT <x1> <x2> <y1> <y2>` - selects a portion of the picture loaded,
swaps the coordinates if they are in the wrong order.

3. `SELECT ALL` - selects the whole picture loaded.

4. `EQUALIZE` - if the loaded picture is a grayscale one, it equalizes it
using the formula provided in the PDF.

5. `CROP` - crops the picture; done by making a copy of the selection,
freeing the old photo and replacing its address with the selection's.

6. `APPLY <FILTER>` - applies one of the 4 filters: EDGE, SHARPEN, BLUR,
GAUSSIAN BLUR. Implemented by using 3x3 Kernel matrices; only works for
PixMap files.

7. `HISTOGRAM <x> <y>` - prints a histogram of the picture loaded, provided
that it is a grayscale one. The histogram is made of `y` bins, while `x` is
the max value of a bin.

8. `SAVE <filename> [ascii]` - saves the loaded picture into <filename>. The
`ascii` parameter is optional, saving the picture in ASCII format. Otherwise,
the picture is saved in binary format.

9. `ROTATE <angle>` - [BONUS] - Only works if the angle is a multiple of 90.
The selection has to either be a square one or be the whole picture. The
rotations are made by a combination of transposing the matrix and reversing
the columns and the rows of the matrix. The functions for reversing the rows
and columns are pretty straight forward, swapping the elements one by one.
The transposing function works differently depending on whether the submatrix
selected is square or not: in the case of a square matrix, the elements
above the main diagonal of the selection are swapped with those under the
diagonal. In the case of a rectangular matrix, a new matrix is allocated and
the transposed values are copied from the old one. The old matrix is then freed
and its address is changed to the new one.