diff --git a/Makefile b/Makefile
index 10e022c5..9c8f0adb 100644
--- a/Makefile
+++ b/Makefile
@@ -126,6 +126,9 @@ rgbfix: ${rgbfix_obj}
 rgbgfx: ${rgbgfx_obj}
 	$Q${CXX} ${REALLDFLAGS} ${PNGLDFLAGS} -o $@ ${rgbgfx_obj} ${REALCXXFLAGS} -x c++ src/version.c ${PNGLDLIBS}
 
+test/randtilegen: test/randtilegen.c
+	$Q${CC} ${REALLDFLAGS} ${PNGLDFLAGS} -o $@ $^ ${REALCFLAGS} -Wno-vla ${PNGCFLAGS} ${PNGLDLIBS}
+
 # Rules to process files
 
 # We want the Bison invocation to pass through our rules, not default ones
diff --git a/test/.gitignore b/test/.gitignore
index 32dd40f7..ecf476f6 100644
--- a/test/.gitignore
+++ b/test/.gitignore
@@ -1,3 +1 @@
-/pokecrystal/
-/pokered/
-/ucity/
+/randtilegen
diff --git a/test/randtilegen.c b/test/randtilegen.c
new file mode 100644
index 00000000..2eccf6b2
--- /dev/null
+++ b/test/randtilegen.c
@@ -0,0 +1,240 @@
+/*
+ * This file is part of RGBDS.
+ *
+ * Copyright (c) 2022, Eldred Habert and RGBDS contributors.
+ *
+ * SPDX-License-Identifier: MIT
+ *
+ * Originally:
+ * // This program is hereby released to the public domain.
+ * // ~aaaaaa123456789, released 2022-03-15
+ * https://gist.github.com/aaaaaa123456789/3feccf085ab4f82d144d9a47fb1b4bdf
+ *
+ * This was modified to use libpng instead of libplum, as well as comments and style changes.
+ */
+
+#include <assert.h>
+#include <inttypes.h>
+#include <limits.h>
+#include <png.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+uint32_t randBits = 0; // Storage for bits read from the input stream but not yet used
+uint8_t randCount = 0; // How many bits are currently stored in the above
+size_t nbRandBytes = 0;
+
+static uint32_t getRandomBits(uint8_t count) {
+	// Trying to read one more byte with `randCount` at least this high will drop some bits
+	// If the count is no higher than that limit, then the loop will exit without reading more bytes
+	assert(count <= sizeof(randBits) * 8 + 1);
+
+	// Read bytes until we have enough bits to serve the request
+	while (count > randCount) {
+		int data = getchar();
+		if (data == EOF) {
+			fprintf(stderr, "Exit after reading %zu bytes\n", nbRandBytes);
+			exit(0);
+		}
+		randBits |= (uint32_t)data << randCount;
+		randCount += 8;
+		++nbRandBytes;
+	}
+
+	uint32_t result = randBits & (((uint32_t)1 << count) - 1);
+	randBits >>= count;
+	randCount -= count;
+	return result;
+}
+
+/**
+ * Expand a 5-bit color component to 8 bits with minimal bias
+ */
+static uint8_t _5to8(uint8_t five) {
+	return five << 3 | five >> 2;
+}
+
+static void generate_random_image(png_structp png, png_infop pngInfo) {
+#define NB_TILES 100
+	struct {
+		unsigned char palette;
+		unsigned char nbColors;
+	} attributes[NB_TILES];
+	uint8_t tileData[NB_TILES][8][8];
+	// These two are in tiles, not pixels
+	// Both width and height are 4-bit values, so nbTiles is 8-bit (OK!)
+	uint8_t const width = getRandomBits(3) + 3, height = getRandomBits(3) + 3,
+	              nbTiles = width * height;
+
+	for (uint8_t p = 0; p < nbTiles; p++) {
+		uint8_t pal;
+		do {
+			pal = getRandomBits(5);
+		} while (pal == 0 || (pal > 29));
+		attributes[p].palette = 2 * pal + getRandomBits(1);
+		// Population count (nb of bits set), the simple way
+		static uint8_t const popcount[] = {1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4,
+		                                   1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4};
+		attributes[p].nbColors = popcount[pal - 1];
+		if (attributes[p].nbColors < 2) {
+			memset(tileData[p], 0, sizeof(tileData[p]));
+			continue;
+		}
+		uint8_t index, total;
+		for (index = 0, total = 0; index < p; index++) {
+			if (attributes[index].nbColors == attributes[p].nbColors) {
+				total++;
+			}
+		}
+		// index == p at exit
+		if (total) {
+			index = getRandomBits(8);
+			if (index < total) {
+				total = index + 1;
+				for (index = 0; total; index++) {
+					if (attributes[index].nbColors == attributes[p].nbColors) {
+						total--;
+					}
+				}
+			} else {
+				index = p;
+			}
+		}
+		if (index != p) {
+			unsigned rotation = getRandomBits(2);
+			for (uint8_t y = 0; y < 8; y++) {
+				for (uint8_t x = 0; x < 8; x++) {
+					tileData[p][y][x] =
+					    tileData[index][y ^ ((rotation & 2) ? 7 : 0)][x ^ ((rotation & 1) ? 7 : 0)];
+				}
+			}
+		} else {
+			switch (attributes[p].nbColors) {
+			case 2:
+				for (uint8_t y = 0; y < 8; y++)
+					for (uint8_t x = 0; x < 8; x++)
+						tileData[p][y][x] = getRandomBits(1);
+				break;
+			case 4:
+				for (uint8_t y = 0; y < 8; y++)
+					for (uint8_t x = 0; x < 8; x++)
+						tileData[p][y][x] = getRandomBits(2);
+				break;
+			default:
+				for (uint8_t y = 0; y < 8; y++)
+					for (uint8_t x = 0; x < 8; x++) {
+						do {
+							index = getRandomBits(2);
+						} while (index == 3);
+						tileData[p][y][x] = index;
+					}
+			}
+		}
+	}
+
+	uint16_t colors[10];
+	for (uint8_t p = 0; p < 10; p++) {
+		colors[p] = getRandomBits(15);
+	}
+	// Randomly make color #0 of all palettes transparent
+	if (!getRandomBits(2)) {
+		colors[0] |= 0x8000;
+		colors[5] |= 0x8000;
+	}
+
+	uint16_t palettes[60][4];
+	for (uint8_t p = 0; p < 60; p++) {
+		const uint16_t *subpal = colors;
+		if (p & 1) {
+			subpal += 5;
+		}
+		uint8_t total = 0;
+		for (uint8_t index = 0; index < 5; index++) {
+			if (p & (2 << index)) {
+				palettes[p][total++] = subpal[index];
+			}
+		}
+	}
+
+	png_set_IHDR(png, pngInfo, width * 8, height * 8, 8, PNG_COLOR_TYPE_RGB_ALPHA,
+	             getRandomBits(1) ? PNG_INTERLACE_NONE : PNG_INTERLACE_ADAM7,
+	             PNG_COMPRESSION_TYPE_DEFAULT, PNG_FILTER_TYPE_DEFAULT);
+
+	// While it would be nice to write the image little by little, I really don't want to handle
+	// interlacing myself. (We're doing interlacing to test that RGBGFX correctly handles it.)
+	uint8_t const SIZEOF_PIXEL = 4; // Each pixel is 4 bytes (RGBA @ 8 bits/component)
+	uint8_t data[height * 8 * width * 8 * SIZEOF_PIXEL];
+	uint8_t *rowPtrs[height * 8];
+	for (uint8_t y = 0; y < height * 8; ++y) {
+		rowPtrs[y] = &data[y * width * 8 * SIZEOF_PIXEL];
+	}
+
+	for (uint8_t p = 0; p < nbTiles; p++) {
+		uint8_t tx = 8 * (p % width), ty = 8 * (p / width);
+		for (uint8_t y = 0; y < 8; y++) {
+			uint8_t * const row = rowPtrs[ty + y];
+			for (uint8_t x = 0; x < 8; x++) {
+				uint8_t * const pixel = &row[(tx + x) * SIZEOF_PIXEL];
+				uint16_t color = palettes[attributes[p].palette][tileData[p][y][x]];
+				pixel[0] = _5to8(color & 0x1F);
+				pixel[1] = _5to8(color >> 5 & 0x1F);
+				pixel[2] = _5to8(color >> 10 & 0x1F);
+				pixel[3] = color & 0x8000 ? 0x00 : 0xFF;
+			}
+		}
+	}
+	png_set_rows(png, pngInfo, rowPtrs);
+	png_write_png(png, pngInfo, PNG_TRANSFORM_IDENTITY, NULL);
+}
+
+int main(int argc, char **argv) {
+	if (argc < 2) {
+		fputs("usage: randtilegen <basename> [<basename> [...]]\n", stderr);
+		return 2;
+	}
+
+	size_t maxBasenameLen = 0;
+	for (int index = 1; index < argc; index++) {
+		size_t length = strlen(argv[index]);
+		if (length > maxBasenameLen) {
+			maxBasenameLen = length;
+		}
+	}
+
+	char filename[maxBasenameLen + 25];
+	for (uint16_t i = 0;; i++) { // 65k images ought to be enough
+		for (int index = 1; index < argc; index++) {
+			sprintf(filename, "%s%" PRIu16 ".png", argv[index], i);
+			FILE *img = fopen(filename, "wb");
+			if (!img) {
+				perror("PNG fopen");
+				return 1;
+			}
+			png_structp png = png_create_write_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
+			if (!png) {
+				perror("png_create_write_struct");
+				return 1;
+			}
+			png_infop pngInfo = png_create_info_struct(png);
+			if (!pngInfo) {
+				perror("png_create_info_struct");
+				return 1;
+			}
+			if (setjmp(png_jmpbuf(png))) {
+				fprintf(stderr, "FATAL: an error occurred while writing image \"%s\"\n", filename);
+				return 1;
+			}
+
+			png_init_io(png, img);
+			generate_random_image(png, pngInfo);
+			png_destroy_write_struct(&png, &pngInfo);
+			fclose(img);
+		}
+
+		if (i == UINT16_MAX) {
+			break;
+		}
+	}
+}