How to convert pixels to RGBA for characters?

Having access to the pixels of any image through the SFML library, my goal is to capture them and convert them to characters by placing them in a new array (image) and then displaying it. For this I checked the size of the image:

sf::Vector2u tam = imagem.getSize();
int largura = tam.x;
int altura  = tam.y;

To capture the RGB format, use the following code:

// O ponteiro dos pixel originais em RGBA.
const sf::Uint8* pixels = imagem.getPixelsPtr();

Pixel* rgba = (Pixel*) pixels;
// Vetor que armazenará os pixels.
sf::Uint8* saida = new sf::Uint8[4 * largura * altura];

int tamanho = 4 * largura * altura;

for (int i = 0; i < tamanho; i++)
{
saida[i] = pixels[i];
}

What I'm doing is creating a vector that is receiving RGBA, but still no conversion to characters, and this is one of my doubts how is a vector how will I control when it should break the line to form the correct image? Home Would not it be better to do with an array?
My other question is how do I convert these pixels into characters?

I tried this way, but to no avail:

for (int i = 0; i < tamanho; i++)
{
if (atriz[i][j]>=9,4*8)
saida[i] = '@';
}