The picture tool of the opensnes-* family (The opensnes-* tools: conventions), for the screens that are not a tileset-and-tilemap: the HiColor technique, and the Mode 7 perspective tables that turn a flat Mode 7 plane into a road receding to the horizon. Both were maintainer scripts until 2026-10 (hicolor64.py, m7ptables.py); they are compiled now, so a game's build needs no Python. A Mode 7 picture is opensnes-tileset convert --mode 7 (opensnes-tileset — pictures to tilesets and tilemaps).

HiColor

opensnes-image hicolor res/sunset.png --save

In: a 256x224 picture, RGB or RGBA (nothing is transparent: the technique reloads whole palettes). Out, beside it or in --out:

File	What it is
sunset.pic	896 sequential 4 bpp tiles (28 tile rows of 32), no deduplication: 28672 bytes of VRAM
sunset.pal	one 16-colour palette per 64x8 segment — 28 rows x 4 segments x 32 bytes = 3584 bytes; colour 0 of each is black, the other 15 are the segment's own
sunset.inc, sunset_data.as	the glue: sunset_tiles, sunset_pal (each with _end), SUNSET_ROWS, SUNSET_SEGMENTS, SUNSET_TILES_SIZE, SUNSET_PAL_SIZE; the .incbin fragment the build gathers

Load the tiles once and stream the palettes into CGRAM from an H-IRQ, 16 bytes per scanline, while the PPU draws: every tile row shows 64 colours of its own, 1792 palette entries on a screen whose mode allows 128. examples/color/hicolor_1792 is the whole mechanism (krom's HiColor64PerTileRow), and its tilemap alternates palette banks 0-3 and 4-7 by tile row so the stream refills one bank while the other displays.

Each segment is quantized to 15 colours by median cut and then --passes rounds of k-means (3 by default; 0 keeps the median cut). The result is deterministic: the same picture gives the same bytes on every OS.

Perspective

opensnes-image perspective res/perspective.toml --angles 48 --zoom 80 --save

A composed asset with no source file: res/perspective.toml holds the parameters and the build regenerates the tables from them.

tool = "opensnes-image"
 
[perspective]
angles = 48     # rotation steps over a full turn
lines = 224     # scanlines per table
zoom = 80       # the scale at the first scanline

For each angle, one HDMA table per Mode 7 matrix term — cos, sin and -sin — with entry(line) = trig(angle) * zoom * 256 / line in 8.8 fixed point: an 80x zoom-out at the top shrinking hyperbolically down the screen, the perspective divide. Each table is lines entries of [count 1][word] and a terminator (673 bytes at 224 lines), in perspective_cos.hdma, perspective_sin.hdma, perspective_nsin.hdma, with perspective.inc (perspective_cos, _sin, _nsin, PERSPECTIVE_ANGLES, _LINES, _STRIDE, _ZOOM) and perspective_data.as.

#include "res/perspective.inc"
 
u16 off = angle * PERSPECTIVE_STRIDE;
hdmaSetup(HDMA_CHANNEL_0, HDMA_MODE_1REG_2X, HDMA_DEST_M7A, perspective_cos + off);
hdmaSetup(HDMA_CHANNEL_1, HDMA_MODE_1REG_2X, HDMA_DEST_M7B, perspective_sin + off);
hdmaSetup(HDMA_CHANNEL_2, HDMA_MODE_1REG_2X, HDMA_DEST_M7C, perspective_nsin + off);
hdmaSetup(HDMA_CHANNEL_3, HDMA_MODE_1REG_2X, HDMA_DEST_M7D, perspective_cos + off);

With the defaults, the tables are krom (Peter Lemon)'s Perspective demo tables byte for byte — examples/mode7/perspective_rotate shipped them verbatim until the tool regenerated them; the tool's golden suite keeps his bytes as the reference. --zoom above 127 is refused: the first scanline's entry would not fit a signed 16-bit Mode 7 term.

Inspect

opensnes-image inspect res/*.png

# sunset.png: 256x224 px, 15885 distinct colours — a HiColor screen; the busiest 64x8 segment has 64 colours in 15-bit (15 kept)

Whether a picture is a HiColor screen and how hard the busiest segment is quantized; --json for a script.

HiColor

Perspective

Inspect

See also