[Term Entry] Python Pillow - Image: .eval()

content/pillow/concepts/image/terms/eval/eval.md

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+---
+Title: '.eval()'
+Description: 'Applies a function to each pixel of an image, returning a new image with modified pixel values.'
+Subjects:
+  - 'Computer science'
+  - 'Data Science'
+Tags:
+  - 'Computer Vision'
+  - 'Images'
+  - 'Pillow'
+  - 'Values'
+CatalogContent:
+  - 'learn-python-3'
+  - 'paths/computer-science'
+---
+
+The **`.eval()`** method in Pillow processes an image by applying a given function to each pixel. This is useful for pixel-level transformations like adjusting brightness, inverting colors, or applying custom filters.
+
+## Syntax
+
+```pseudo
+Image.eval(image, function)
+```
+
+- `image`: The input image object to process.
+- `function`: A function/lambda that takes one integer argument (the pixel value) and returns a modified integer.
+
+## Example
+
+The example below converts the input image into a new image, where each pixel is transformed by a function:
+
+```py
+from PIL import Image
+
+# Open an image
+img = Image.open('media/pillow-original.jpeg').convert("RGB")  # Ensure RGB mode
+
+# Define a function to invert pixel values
+def invert_pixel(x):
+  return 255 - x  # Works for grayscale and individual RGB channels
+
+# Apply the function to each pixel
+new_img = Image.eval(img, invert_pixel)
+
+# Display the new image
+new_img.show()
+```
+
+In this example:
+
+- `x`: Represents the pixel intensity value, which typically ranges from 0-255 (for 8-bit grayscale or RGB images).
+- `255 - x`: Subtracts the pixel value from 255, effectively inverting its brightness: 0 → 255 (pure black becomes pure white), 255 → 0 (pure white becomes pure black), 100 → 155 (mid-gray becomes a lighter gray).
+
+Here is the original image:
+
+![Original Image](https://raw.githubusercontent.com/Codecademy/docs/main/media/pillow-original.jpeg)
+
+Here is the updated image:
+
+![Updated Image](https://raw.githubusercontent.com/Codecademy/docs/main/media/pillow-eval.png)