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Problem

You need to resize, rotate, crop, or convert hundreds of images—and keep track of all the transformed versions.

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Solution

What’s in this recipe:
  • Basic image operations (resize, rotate, flip, crop)
  • Track image properties
  • Iterate on transformations before adding to your table
You apply PIL transformations (resize, rotate, flip, crop) to images in your table using Pixeltable’s built-in image functions—common operations that work directly on image columns. You can iterate on transformations before adding them to your table. Use .select() with .collect() to preview results on sample images—nothing is stored in your table. If you want to collect only the first few rows, use .head(n) instead of .collect(). Once you’re satisfied, use .add_computed_column() to apply the transformation to all images in your table. For more on this workflow, see Get fast feedback on transformations.

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Setup

%pip install -qU pixeltable

import pixeltable as pxt

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Load images

# Create a fresh directory (drop existing if present)
pxt.drop_dir('image_demo', force=True)
pxt.create_dir('image_demo')

Connected to Pixeltable database at: postgresql+psycopg://postgres:@/pixeltable?host=/Users/alison-pxt/.pixeltable/pgdata
Created directory ‘image_demo’.
<pixeltable.catalog.dir.Dir at 0x129fa1e00>
t = pxt.create_table('image_demo.images', {'image': pxt.Image})

Created table ‘images’.
t.insert([
    {'image': 'https://raw.githubusercontent.com/pixeltable/pixeltable/main/docs/resources/images/000000000285.jpg'},
    {'image': 'https://raw.githubusercontent.com/pixeltable/pixeltable/main/docs/resources/images/000000000776.jpg'},
    {'image': 'https://raw.githubusercontent.com/pixeltable/pixeltable/main/docs/resources/images/000000000885.jpg'},
])

Inserting rows into `images`: 3 rows [00:00, 1107.85 rows/s]
Inserted 3 rows with 0 errors.
3 rows inserted, 6 values computed.

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Iterate: Check image properties for a few images first

Use .select() to define the transformation, then .collect() to execute and return results. If you want to collect only the first few rows, use .head(n) instead of .collect(). Nothing is stored in your table. Pixeltable includes these built-in functions for image properties: - .height - Get image height in pixels - .width - Get image width in pixels - .mode - Get color mode (RGB, RGBA, L for grayscale, etc.) 
# Preview the properties
t.select(t.image, t.image.height, t.image.width, t.image.mode).collect()

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Add: Check image properties for all images in your table

# Save as computed columns
t.add_computed_column(height=t.image.height)
t.add_computed_column(width=t.image.width)
t.add_computed_column(mode=t.image.mode)  # RGB, RGBA, L (grayscale), etc.

Added 3 column values with 0 errors.
Added 3 column values with 0 errors.
Added 3 column values with 0 errors.
3 rows updated, 6 values computed.
# View images with computed height, width, and mode columns
t.collect()

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Iterate: Resize a few images first

Use .select() to define the transformation, then .collect() to execute and return results. If you want to collect only the first few rows, use .head(n) instead of .collect(). Nothing is stored in your table. Pixeltable includes a built-in function for resizing image files with PIL:
  • .resize(width, height) - Change image dimensions
# Preview the resize operation
t.select(t.image, t.image.resize((224, 224))).head(1)

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Add: Resize all images in your table

Once you’re satisfied with the results, use .add_computed_column() with the same expression. This processes all rows and stores the results permanently in your table. 
# Save as computed column
t.add_computed_column(resized=t.image.resize((224, 224)))

Added 3 column values with 0 errors.
3 rows updated, 3 values computed.
# View images with resized column
t.collect()

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Iterate: Rotate a few images first

Use .select() to define the transformation, then .collect() to execute and return results. If you want to collect only the first few rows, use .head(n) instead of .collect(). Nothing is stored in your table. Pixeltable includes a built-in function for rotating image files with PIL:
  • .rotate(degrees) - Rotate image by specified degrees
# Preview the rotation
t.select(t.image, t.image.rotate(90)).head(1)

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Add: Rotate all images in your table

Once you’re satisfied with the results, use .add_computed_column() with the same expression. This processes all rows and stores the results permanently in your table. 
# Save as computed column
t.add_computed_column(rotated=t.image.rotate(90))

Added 3 column values with 0 errors.
3 rows updated, 3 values computed.
# View images with rotated column
t.collect()

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Iterate: Flip a few images first

Use .select() to define the transformation, then .collect() to execute and return results. If you want to collect only the first few rows, use .head(n) instead of .collect(). Nothing is stored in your table. Pixeltable includes a built-in function for transposing image files with PIL (note that for this transform you will need import PIL to access the FLIP_* constants):
  • .transpose(Image.FLIP_TOP_BOTTOM) - Flip image vertically
  • .transpose(Image.FLIP_LEFT_RIGHT) - Mirror image horizontally
# Import PIL Image to access flip constants
from PIL import Image

# Preview both flip operations
t.select(
    t.image,
    t.image.transpose(Image.FLIP_TOP_BOTTOM),
    t.image.transpose(Image.FLIP_LEFT_RIGHT)
).head(1)

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Add: Flip all images in your table

Once you’re satisfied with the results, use .add_computed_column() with the same expression. This processes all rows and stores the results permanently in your table. 
# Flip vertically (top to bottom)
t.add_computed_column(flip_v=t.image.transpose(Image.FLIP_TOP_BOTTOM))

# Flip horizontally (left to right, mirror effect)
t.add_computed_column(flip_h=t.image.transpose(Image.FLIP_LEFT_RIGHT))

Added 3 column values with 0 errors.
Added 3 column values with 0 errors.
3 rows updated, 3 values computed.
# View original and flipped versions side by side
t.select(t.image, t.flip_v, t.flip_h).collect()

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Iterate: Crop a few images first

Use .select() to define the transformation, then .collect() to execute and return results. If you want to collect only the first few rows, use .head(n) instead of .collect(). Nothing is stored in your table. Pixeltable includes a built-in function for cropping image files with PIL:
  • .crop(box) - Extract a rectangular region from the image (box format: (left, top, right, bottom))
# Preview the center crop
# Box format: (left, top, right, bottom)
t.select(
    t.image,
    t.image.crop((
        t.image.width // 4,
        t.image.height // 4,
        3 * t.image.width // 4,
        3 * t.image.height // 4
    ))
).head(1)

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Add: Crop all images in your table

Once you’re satisfied with the results, use .add_computed_column() with the same expression. This processes all rows and stores the results permanently in your table. 
# Save as computed column
t.add_computed_column(
    center_crop=t.image.crop((
        t.image.width // 4,
        t.image.height // 4,
        3 * t.image.width // 4,
        3 * t.image.height // 4
    ))
)

Added 3 column values with 0 errors.
3 rows updated, 3 values computed.
# View center-cropped images
t.select(t.center_crop).collect()

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Explanation

How PIL transformations work in Pixeltable: Pixeltable provides built-in functions that wrap PIL (Pillow) operations for image manipulation. These functions work directly on image columns in your table—no need to write loops or manage file I/O. When you call .resize(), .rotate(), or other methods on an image column, Pixeltable handles applying the transformation to each image automatically. All these transformations use standard PIL operations under the hood. For more details on PIL functionality, see the Pillow documentation. To customize transformations:
  • Resize: Change dimensions with .resize((width, height)) - specify target size in pixels
  • Rotate: Rotate counterclockwise with .rotate(degrees) - use negative values for clockwise rotation
  • Flip: Use .transpose(Image.FLIP_LEFT_RIGHT) for horizontal mirror or .transpose(Image.FLIP_TOP_BOTTOM) for vertical flip
  • Crop: Extract regions with .crop((left, top, right, bottom)) - coordinates are in pixels from top-left origin
  • Properties: Access .width, .height, and .mode to get image dimensions and color mode
The Pixeltable workflow: In traditional databases, .select() just picks which columns to view. In Pixeltable, .select() also lets you compute new transformations on the fly—define new columns without storing them. This makes .select() perfect for testing transformations before you commit them. When you use .select(), you’re creating a query that doesn’t execute until you call .collect(). You must use .collect() to execute the query and return results—nothing is stored in your table. If you want to collect only the first few rows, use .head(n) instead of .collect() to test on a subset before processing your full dataset. Once satisfied, use .add_computed_column() with the same expression to persist results permanently. For more on this workflow, see Get fast feedback on transformations.

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See also