How do I omit empty (black) tiles from a QGIS raster export?

Question

At the moment I'm deleting these manually after export and I'm curious if there's another way.

I've currently imported a transparent TIFF layer and georeferenced it to Bing. I'm then exporting with Raster Tools > Generate XYZ Tiles (Directory).

This process is working great, but it's exporting all of the fully transparent (blank) areas as black files that I have to then manually delete later.

Is there some way to simply omit these during export?

Here's the example area if it's helpful for some reason:

Answer 1

You can use the python img.getbbox method to identify and remove transparent images.

import os
from PIL import Image
if img.getbbox() is None:
    os.remove(path)

Just copy the following code into a file with '.py' extension and place this file into your QGIS folder with python scripts. It should be this path in Windows:

C:\Users\username\AppData\Roaming\QGIS\QGIS3\profiles\default\processing\scripts

or in Linux:

/home/username/.local/share/QGIS/QGIS3/profiles/default/processing/scripts

After restarting QGIS you'll find the script in the bottom of the processing toolbox in QGIS. Choose the path of the folder with tiles. It will look through all subfolders, identify transparent tiles, delete them and also delete all empty folders. It also works well in the model designer.

I didn't test it with other formats than png. You can try it by replacing png in the code with another format that also is transparent.

from qgis.core import QgsProcessing
from qgis.core import QgsProcessingAlgorithm
from qgis.core import QgsProcessingParameterFolderDestination
from qgis.core import QgsProcessingMultiStepFeedback
import processing
from PIL import Image
import os

class deleteemptytiles(QgsProcessingAlgorithm):
    def initAlgorithm(self, config=None):
        # Add a folder input parameter to the algorithm
        self.addParameter(
            QgsProcessingParameterFolderDestination(
                'INPUT_FOLDER',
                'Input Folder containing tiles'
            )
        )

    def processAlgorithm(self, parameters, context, model_feedback):
        feedback = QgsProcessingMultiStepFeedback(1, model_feedback)
        results = {}
        outputs = {}

        # Retrieve the folder path from the parameter
        tile_folder = self.parameterAsFile(parameters, 'INPUT_FOLDER', context)

        # Delete transparent tiles
        for root, dirs, files in os.walk(tile_folder, topdown=False):
            for filename in files:
                if filename.endswith('.png'):
                    path = os.path.join(root, filename)
                    try:
                        img = Image.open(path)
                        if img.getbbox() is None:  # Check if the image is fully transparent
                            os.remove(path)
                            feedback.pushInfo(f"Deleted {filename}")
                    except Exception as e:
                        feedback.reportError(f"Error processing {filename}: {str(e)}")

        # Remove empty folders
        for root, dirs, files in os.walk(tile_folder, topdown=False):
            for dir in dirs:
                dirpath = os.path.join(root, dir)
                if not os.listdir(dirpath):  # Check if the directory is empty
                    os.rmdir(dirpath)
                    feedback.pushInfo(f"Removed empty directory {dirpath}")

        return results

    def name(self):
        return 'DeleteEmptyTiles'

    def displayName(self):
        return 'Delete empty tiles and directories'

    def group(self):
        return ''

    def groupId(self):
        return ''

    def createInstance(self):
        return deleteemptytiles()