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73 lines
2.6 KiB
Python
73 lines
2.6 KiB
Python
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import json
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import os
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from io import BytesIO
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from PIL import Image
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"""
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A template is two files:
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NAME.png
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NAME.json
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The image is the template image itself.
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The JSON file contains the following:
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{
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crop: BOX,
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location: BOX,
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}
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where BOX is a 4-tuple [left x, top y, right x, bottom y] describing a rectangle in image coordinates.
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To create a thumbnail, the input frame is first cropped to the bounds of the "crop" box,
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then resized to the size of the "location" box, then pasted underneath the template image at that
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location within the template image.
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For example, a JSON file of:
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{
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"crop": [50, 100, 1870, 980],
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"location": [320, 180, 1600, 900]
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}
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would crop the input frame from (50, 100) to (1870, 980), resize it to 720x1280,
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and place it at (320, 180).
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If the original frame and the template differ in size, the frame is first resized to the template.
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This allows you to work with a consistent coordinate system regardless of the input frame size.
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"""
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def compose_thumbnail_template(base_dir, template_name, frame_data):
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template_path = os.path.join(base_dir, "thumbnail_templates", f"{template_name}.png")
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info_path = os.path.join(base_dir, "thumbnail_templates", f"{template_name}.json")
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template = Image.open(template_path)
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# PIL can't load an image from a byte string directly, we have to pretend to be a file
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frame = Image.open(BytesIO(frame_data))
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with open(info_path) as f:
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info = json.load(f)
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crop = info['crop']
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loc_left, loc_top, loc_right, loc_bottom = info['location']
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location = loc_left, loc_top
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location_size = loc_right - loc_left, loc_bottom - loc_top
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# Create a new blank image of the same size as the template
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result = Image.new('RGBA', template.size)
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# If the frame is not the same size, scale it so it is.
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# For choice of rescaling filter, pick LANCZOS (aka. ANTIALIAS) as it is highest quality
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# and we don't really care about performance.
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if frame.size != template.size:
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frame = frame.resize(template.size, Image.LANCZOS)
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# Insert the frame at the desired location, cropping and scaling.
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# Technically we might end up resizing twice here which is bad for quality,
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# but the case of frame size != template size should be rare enough that it doesn't matter.
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frame = frame.crop(crop).resize(location_size, Image.LANCZOS)
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result.paste(frame, location)
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# Place the template "on top", letting the frame be seen only where the template's alpha
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# lets it through.
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result.alpha_composite(template)
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buf = BytesIO()
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# PIL can't save an image to a byte string directly, we have to pretend to write it to
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# a file, rewind the file, then read it again.
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result.save(buf, format='png')
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buf.seek(0)
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return buf.read()
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