Corner-to-Corner (C2C) (C2C)

Intermediate Technique

A blanket-building technique worked diagonally in growing, then shrinking, blocks of double crochet — popular for graphghan-style pixel patterns.

Chain 6, then work 1 double crochet into the 4th chain from the hook and 1 double crochet into each of the next 2 chains — this makes your first 3-double-crochet block.
To start each new row, chain 6 and turn; work 1 double crochet into the 4th chain from the hook and the next 2 chains to make a new starting block.
Slip stitch into the chain-2 space of the previous block to connect, then chain 3 and work 3 double crochet into the same space for the next block.
Continue across the row, working one 3-double-crochet block into each chain-space of the row below, adding one new block at the start of every row until you reach your intended width.
To shape the second half of the blanket, stop adding new blocks and instead join into the second chain-space in from the edge, reducing the block count by one each row until a single block remains.

Each diagonal row is one block longer while increasing, and one block shorter while decreasing — that symmetry is what keeps C2C blankets square.
C2C reads especially well for pixel-style graphs, since each block can be a single "pixel" of color.
Keep your chain-6 turning chains consistent in tension — loose or tight turns are the most common cause of a C2C blanket drifting off-square.