Problems with nxjpeg

[toncho11]

1. There is a shift to the left of the image, by 1 MCU

2. Artifact left corner

3. Colors in 16 color mode are not good. Even if you first convert to ega 16, it still goes wrong. There must be detection if the image is close to 16 color ega, then do not process it.

4. Smooting can have an error.

[toncho11]

#!/usr/bin/env bash
set -e

PNG_OUT="ega16_palette_strip.png"
JPG_OUT="ega16_palette_strip.jpg"
SWATCH=16   # Pico-friendly size (16x16 per color)

# Canonical EGA 16-color palette
PALETTE=(
  "#000000" "#0000AA" "#00AA00" "#00AAAA"
  "#AA0000" "#AA00AA" "#AA5500" "#AAAAAA"
  "#555555" "#5555FF" "#55FF55" "#55FFFF"
  "#FF5555" "#FF55FF" "#FFFF55" "#FFFFFF"
)

convert \
  \( -size ${SWATCH}x${SWATCH} xc:${PALETTE[0]}  \) \
  \( -size ${SWATCH}x${SWATCH} xc:${PALETTE[1]}  \) \
  \( -size ${SWATCH}x${SWATCH} xc:${PALETTE[2]}  \) \
  \( -size ${SWATCH}x${SWATCH} xc:${PALETTE[3]}  \) \
  \( -size ${SWATCH}x${SWATCH} xc:${PALETTE[4]}  \) \
  \( -size ${SWATCH}x${SWATCH} xc:${PALETTE[5]}  \) \
  \( -size ${SWATCH}x${SWATCH} xc:${PALETTE[6]}  \) \
  \( -size ${SWATCH}x${SWATCH} xc:${PALETTE[7]}  \) \
  \( -size ${SWATCH}x${SWATCH} xc:${PALETTE[8]}  \) \
  \( -size ${SWATCH}x${SWATCH} xc:${PALETTE[9]}  \) \
  \( -size ${SWATCH}x${SWATCH} xc:${PALETTE[10]} \) \
  \( -size ${SWATCH}x${SWATCH} xc:${PALETTE[11]} \) \
  \( -size ${SWATCH}x${SWATCH} xc:${PALETTE[12]} \) \
  \( -size ${SWATCH}x${SWATCH} xc:${PALETTE[13]} \) \
  \( -size ${SWATCH}x${SWATCH} xc:${PALETTE[14]} \) \
  \( -size ${SWATCH}x${SWATCH} xc:${PALETTE[15]} \) \
  +append \
  -strip \
  -alpha off \
  -type TrueColor \
  "$PNG_OUT"

# JPG version (still lossy, but stripped)
convert "$PNG_OUT" \
  -strip \
  -quality 100 \
  -sampling-factor 4:4:4 \
  "$JPG_OUT"

echo "Generated Pico-compatible palette strip:"
echo "  $PNG_OUT"
echo "  $JPG_OUT"