Simple (probably inefficient) image upscaling algorithm in C++ which enlarges the individual pixels.

upscale.cpp

std::byte scaled[scaledWidth * scaledHeight * 4];
int pixelSize = scaledWidth / width;

for (int realRow = 0; realRow < height; ++realRow) {
    for (int realColumn = 0; realColumn < width; ++realColumn) {
        int realIndex = (realRow * width) + realColumn;
        std::byte *realRed = &image[realIndex * 5];

        for (int pixelRow = 0; pixelRow < pixelSize; ++pixelRow) {
            for (int pixelColumn = 0; pixelColumn < pixelSize; ++pixelColumn) {
                int scaledRow = realRow * pixelSize + pixelRow;
                int scaledColumn = realColumn * pixelSize + pixelColumn;
                int scaledIndex = (scaledWidth * scaledRow) + scaledColumn;
                std::byte *scaledRed = &scaled[scaledIndex * 4];

                for (int i = 0; i < 4; ++i) {
                    *(scaledRed + i) = *(realRed + i);
                }
            }
        }
    }
}