This is my WIP patch for GSoC and I worked on transformations involved in
encoding/decoding FLIF images. I have created a module under libavcodec and
as guided by my mentors I have tried to use pixel data from AVFrame structs.
Module covers all the chunks of code for YCoCg Transformation that will be
used in final encoder/decoder. Necessary structs and methods have been made
as suggested by my mentors. The module compiles/builds successfully.
Also I have attached a small code 'transformtest.c' which I wrote for
testing the implementation of pixel transformation.
The variable AVFrame::data[] is of type uint8_t* and I was initially
unaware of this so I stored the YCoCg values in 'data'. So the negative
values which were the output of transformation of RGB -> YCoCg were not
stored properly and thats where the output is wrong.
Just wanted to ask, if I should be using some other structs for storing the
YCoCg values and not AVFrame, because AVFrame seems to be the standard
struct in FFmpeg where the raw media resides.
Attaching some testcases of RGB and its corresponding YCoCg values for
testing purposes.
Thanks
Kartik K. Khullar
#include "transformflif16.h"
int process(Transform transform, AVFrame *frame, int p){
switch(transform.transform_number){
case 1: //Transform number for YCoCg transformation is 1 officially.
if(!transform.done){
TransformYCoCg transformYCoCg = initYCoCg(frame, p);
if(!processYCoCg(frame))
transform.done = 1;
return 0;
}
break;
/*
Rest of the cases will be implemented here.
*/
default:
break;
}
return 0;
}
TransformYCoCg initYCoCg(AVFrame *frame, int p){
TransformYCoCg transform;
transform.num_planes = p;
transform.ranges = getRanges(transform.num_planes, frame);
transform.origmax4 = max(transform.ranges[0].max, transform.ranges[1].max, transform.ranges[2].max)/4 -1;
for(p=0; pdata[0][r*width + c];
G = frame->data[1][r*width + c];
B = frame->data[2][r*width + c];
Y = (((R + B)>>1) + G)>>1;
Co = R - B;
Cg = G - ((R + B)>>1);
frame->data[0][r*width + c] = Y;
frame->data[1][r*width + c] = Co;
frame->data[2][r*width + c] = Cg;
}
}
return 0;
}
int invProcessYCoCg(AVFrame *frame){
int r, c;
ColorVal R,G,B,Y,Co,Cg;
//Assuming all the channels will have same width and height
int height = frame[0].height;
int width = frame[0].width;
for (r=0; rdata[0][r*width + c];
Co= frame->data[1][r*width + c];
Cg= frame->data[2][r*width + c];
R = Co + Y + ((1-Cg)>>1) - (Co>>1);
G = Y - ((-Cg)>>1);
B = Y + ((1-Cg)>>1) - (Co>>1);
frame->data[0][r*width + c] = R;
frame->data[1][r*width + c] = G;
frame->data[2][r*width + c] = B;
}
}
return 0;
}
ColorRanges* getRanges(int p, AVFrame *frame){
ColorRanges ranges[p];
int i, c, r, width, height;
uint8_t min, max;
for(i=0; idata[p][0];
max = frame->data[p][0];
for(r=0; r frame->data[p][r*width + c])
min = frame->data[p][r*width + c];
if(max < frame->data[p][r*width + c])
max = frame->data[p][r*width + c];
}
}
ranges[p].min = min;
ranges[p].max = max;
}
return ranges;
}
int max(int a, int b, int c){
if(a > b){
if(a > c)
return a;
else
return c;
}
else
return b;
}
int min(int a, int b){
if(a < b)
return a;
else
return b;
}
int get_min_y(int origmax4){
return 0;
}
int get_max_y(int origmax4){
return 4*origmax4-1;
}
int get_min_co(int origmax4, int yval){
int newmax = 4*origmax4 - 1;
if (yval < origmax4-1)
return -3 - 4*yval;
else if (yval >= 3*origmax4)
return 4*(yval - newmax);
else
return -newmax;
}
int get_max_co(int origmax4, int yval){
int newmax = 4*origmax4 - 1;
if (yval < origmax4-1)
return 3 + 4*yval;
else if (yval >= 3*origmax4)
return 4*(newmax - yval);
else
return newmax;
}
int get_min_cg(int origmax4, int yval, int coval){
int newmax = 4*origmax4 - 1;
if (yval < origmax4-1)
return -2 - 2*yval;
else if (yval >= 3*origmax4)
return -2*(newmax-yval) + 2*((abs(coval)+1)/2);
else{
return min(2*yval + 1, 2*newmax - 2*yval - 2*abs(coval)+1)/2;
}
}
int get_max_cg(int origmax4, int yval, int coval){
int newmax = 4*origmax4 - 1;
if (yval < origmax4-1)
return 1 + 2*yval - 2*(abs(coval)/2);
else if (yval >= 3*origmax4)
return 2 * (newmax-yval);
else
return min(2*(yval- newmax), -2*yval - 1 + 2*(abs(coval)/2));
}
int min_range_YCoCg(int p, int origmax4){
switch(p){
case 0:
return 0;
case 1:
return -4*origmax4+1;
case 2:
return -4*origmax4+1;
default:
return 0;
break;
}
}
int
