How to Convert Between JPG and PNG in Python

pip install Pillow

from PIL import Image

from PIL import Image

def jpg_to_png(source_path, dest_path):
    """Convert JPG to PNG format."""
    img = Image.open(source_path)
    img.save(dest_path, 'PNG')

jpg_to_png("photo.jpg", "photo.png")

from PIL import Image

def jpg_to_png_optimized(source_path, dest_path, compress_level=6):
    """
    Convert JPG to PNG with compression.
    
    Args:
        compress_level: 0-9, higher = smaller file but slower
    """
    img = Image.open(source_path)
    img.save(dest_path, 'PNG', optimize=True, compress_level=compress_level)

jpg_to_png_optimized("photo.jpg", "photo.png")

from PIL import Image

img = Image.open("logo_transparent.png")
img.save("logo.jpg")  # OSError: cannot write mode RGBA as JPEG

from PIL import Image

def png_to_jpg(source_path, dest_path, background_color=(255, 255, 255), quality=95):
    """
    Convert PNG to JPG with proper transparency handling.
    
    Args:
        background_color: RGB tuple for transparent areas (default: white)
        quality: JPG quality 1-100
    """
    img = Image.open(source_path)
    
    if img.mode in ('RGBA', 'LA', 'P'):
        background = Image.new('RGB', img.size, background_color)
        
        if img.mode == 'P':
            img = img.convert('RGBA')
        
        if img.mode == 'RGBA':
            background.paste(img, mask=img.split()[3])
        else:
            background.paste(img, mask=img.split()[1])  # LA mode
        
        background.save(dest_path, 'JPEG', quality=quality)
    else:
        img.convert('RGB').save(dest_path, 'JPEG', quality=quality)

png_to_jpg("logo_transparent.png", "logo.jpg")  # White background
png_to_jpg("icon.png", "icon.jpg", background_color=(0, 0, 0))  # Black background

from PIL import Image

def png_to_jpg_simple(source_path, dest_path, quality=95):
    """
    Simple PNG to JPG conversion.
    Warning: Transparent areas become BLACK.
    """
    img = Image.open(source_path)
    rgb_img = img.convert('RGB')
    rgb_img.save(dest_path, 'JPEG', quality=quality)

png_to_jpg_simple("photo.png", "photo.jpg")

from PIL import Image

def analyze_image(path):
    """Check image properties before conversion."""
    img = Image.open(path)
    
    info = {
        'path': path,
        'format': img.format,
        'mode': img.mode,
        'size': img.size,
        'has_transparency': img.mode in ('RGBA', 'LA', 'P'),
    }
    
    if img.mode == 'P':
        info['has_transparency'] = 'transparency' in img.info
    
    return info

print(analyze_image("unknown.png"))

from PIL import Image
from pathlib import Path

def batch_png_to_jpg(input_dir, output_dir=None, background=(255, 255, 255)):
    """Convert all PNGs in a directory to JPGs."""
    input_path = Path(input_dir)
    output_path = Path(output_dir) if output_dir else input_path
    output_path.mkdir(parents=True, exist_ok=True)
    
    converted = 0
    
    for png_file in input_path.glob("*.png"):
        try:
            img = Image.open(png_file)
            
            if img.mode in ('RGBA', 'LA', 'P'):
                if img.mode == 'P':
                    img = img.convert('RGBA')
                
                bg = Image.new('RGB', img.size, background)
                if img.mode == 'RGBA':
                    bg.paste(img, mask=img.split()[3])
                else:
                    bg.paste(img, mask=img.split()[1])
                img = bg
            else:
                img = img.convert('RGB')
            
            output_file = output_path / f"{png_file.stem}.jpg"
            img.save(output_file, 'JPEG', quality=90)
            converted += 1
            
        except Exception as e:
            print(f"Error converting {png_file.name}: {e}")
    
    print(f"Converted {converted} files")

batch_png_to_jpg("images/", "converted/")

from PIL import Image
from pathlib import Path

def batch_jpg_to_png(input_dir, output_dir=None):
    """Convert all JPGs in a directory to PNGs."""
    input_path = Path(input_dir)
    output_path = Path(output_dir) if output_dir else input_path
    output_path.mkdir(parents=True, exist_ok=True)
    
    for jpg_file in input_path.glob("*.jpg"):
        img = Image.open(jpg_file)
        output_file = output_path / f"{jpg_file.stem}.png"
        img.save(output_file, 'PNG', optimize=True)
    
    for jpeg_file in input_path.glob("*.jpeg"):
        img = Image.open(jpeg_file)
        output_file = output_path / f"{jpeg_file.stem}.png"
        img.save(output_file, 'PNG', optimize=True)

batch_jpg_to_png("photos/", "png_output/")

from PIL import Image
from PIL.ExifTags import TAGS

def convert_preserving_metadata(source, dest, target_format):
    """Convert image while preserving EXIF metadata."""
    img = Image.open(source)
    
    exif = img.info.get('exif')
    
    if target_format.upper() == 'JPEG' and img.mode in ('RGBA', 'P'):
        if img.mode == 'P':
            img = img.convert('RGBA')
        background = Image.new('RGB', img.size, (255, 255, 255))
        background.paste(img, mask=img.split()[3])
        img = background
    elif target_format.upper() == 'JPEG':
        img = img.convert('RGB')
    
    if exif:
        img.save(dest, target_format, exif=exif, quality=95)
    else:
        img.save(dest, target_format, quality=95)

convert_preserving_metadata("photo.png", "photo.jpg", "JPEG")

from PIL import Image

def convert_and_resize(source, dest, max_size=(1920, 1080), background=(255, 255, 255)):
    """Convert format and resize in one operation."""
    img = Image.open(source)
    
    img.thumbnail(max_size, Image.Resampling.LANCZOS)
    
    is_jpg = dest.lower().endswith(('.jpg', '.jpeg'))
    
    if is_jpg:
        if img.mode in ('RGBA', 'LA', 'P'):
            if img.mode == 'P':
                img = img.convert('RGBA')
            bg = Image.new('RGB', img.size, background)
            if img.mode == 'RGBA':
                bg.paste(img, mask=img.split()[3])
            else:
                bg.paste(img, mask=img.split()[1])
            img = bg
        else:
            img = img.convert('RGB')
        img.save(dest, 'JPEG', quality=90)
    else:
        img.save(dest, 'PNG', optimize=True)

convert_and_resize("large_logo.png", "thumbnail.jpg", max_size=(200, 200))