NES Pixel Art Conversion Algorithm

[NES Final Specification & Complete Version: BG Dedicated Algorithm Execution Dot Art Conversion Prompt]

This image is not limited to a specific subject, but is strictly followed by the following mathematical and logical steps
Please convert it to the BG pixel art of the actual Family Computer (NES) specifications.

This prompt aims to satisfy the "constraint that can be established as BG on the actual NES system."
Appearance-only NES-style expressions are prohibited.
Only the BG layer is used, and sprites are not used at all.

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[Prerequisites (NES BG Implementation Rules)]
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- Output resolution: 256 × 240 pixels
- Layer used: NES BG only
- Sprite use is prohibited
- Do not perform transparent processing
- Index 0 in each palette is treated as the NES universal background color
- Index 0 is common to all palettes
- For universal background colors, assign the color with the widest area across the entire screen
- Color number 0 can also be used as a standard drawing color

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[Step 1: Geometric Image Processing (Focus Priority, No Distortion Cropping)]
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1. Set the target size to 256 × 240 pixels
2. Always maintain the aspect ratio of the original image
- Expand or shrink the short side until it fits the destination to be converted
- Stretching the image is strictly prohibited
3. Automatically detects the main subjects in the image (such as people, animals, buildings, etc.),
Adjust the crop position so that the main character fits as much as possible within the frame
4. If the main character cannot be detected, crop it to the center of the screen

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[Step 2: Tile Decomposition and Attribute Block Definition (NES Compliant)]
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1. Divide the image into tiles of 8×8 pixels
2. Treat 2×2 tiles (16×16 pixels) as 1 attribute blocks
3. From now on, palette and color constraints must be applied on a per-block basis of attributes

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[Step 3: Attribute Block Pallet Clustering (Up to 4 Units)]
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1. Analyze the color distribution within each 16×16 attribute block
2. Cluster all attribute blocks by similarity in color distribution, classifying them into up to four groups
3. If the hue (such as blue or green) is clearly different from other areas, treat it as an independent group whenever possible
4. However, the NES BG subpallets can be limited to a maximum of 4 pallets,
Prioritize the main area, and the less important area may be integrated into the approximate color

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[Step 4: NES BG Palette Generation (4 colors × 4 pieces)]
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1. Index 0 (Universal background color)
- Calculate the color with the widest usage area across the entire screen,
Assign it to Index 0, which is common to all pallets
2. Index 1–3 (Intrinsic Colors)
- For each subpalette,
The three colors representing the 'light, intermediate, and dark sections' of each attribute group are selected
- Colors with hue or brightness extremely close to Index 0 are prohibited

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[NES Color Palette Restrictions (Actual Machine Compliant, NTSC)]
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- Available colors are limited to the 54 NTSC palette colors that comply with the NES actual system listed below
- Palette generation, color selection, and quantization must always be performed from this set of 54 colors
- Generating new colors, RGB interpolation, and using continuous values are prohibited
- The following color sets are exactly 54 colors

NES NTSC usable palette (54 colors, hex RGB)
000000,1D2B53,7E2553,#008751,AB5236,5F574F,
C2C3C7,FFF1E8,FF004D,FFA300,FFEC27,00E436,
29ADFF,83769C,FF77A8,FFCCAA,291814,111D35,
422136,125359,742F29,49333B,A28879,F3EF7D,
BE2633,E06F8B,E0A872,B2DCEF,4F6781,8E478C,
A3CE27,44891A,2A4F3E,6D758D,9D9D9D,FFFFFF,
4B692F,6A6A6A,8F563B,C2C3C7,DF7126,D95763,
D77BBA,FBF236,99E550,6ABE30,37946E,5FCDE4,
CBDBFC,ADB5BD,EEC39A,696A6A

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[Step 5: CHR Pattern Compression (BG 256 tile limit)]
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1. Calculate the number of unique 8×8 tile patterns used throughout the image
2. Limit the number of unique tiles to no more than 256
3. Wide areas such as backgrounds, skies, and walls
Completely identical dot patterns are repeatedly used, minimizing the number of tile types to the utmost
4. Tiles with subtle differences may be merged using the following methods
- Readjust the placement of the dither
- Replacing intermediate colors
- Requantization within attribute blocks

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[Step 6: Dithering (Compatible with NES 4-color restrictions)]
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1. Within each attribute block, only the four assigned colors are used
2. To represent pseudo-tonality, stack the following diithers