Building internal Index for 1 tile(s) ... finished
Filename: test_sum.vrt
File Size: 1178083x2179667x1
Pixel Size: 0.780877 x -0.780877
UL:(10841319.553138,2329047.665115)   LR:(11761257.511933,626995.763142)
tileWidth:   2048
tileHeight:  2048
countTilesX: 576
countTilesY: 1065
overlap:     0
Killed

mkdir pyramid
gdal_retile.py -v -r bilinear -levels 5 -ps 2048 2048 -co "TILED=YES" -co "COMPRESS=JPEG" -targetDir pyramid test_sum.vrt

<VRTDataset rasterXSize="1178083" rasterYSize="2179667">
  <SRS>...</SRS>
  <GeoTransform>...</GeoTransform>
  <VRTRasterBand dataType="Byte" band="1" subClass="VRTDerivedRasterBand">
    <PixelFunctionType>max</PixelFunctionType>
    <PixelFunctionLanguage>Python</PixelFunctionLanguage>
    <PixelFunctionCode><![CDATA[
import numpy as np
def max(in_ar, out_ar, xoff, yoff, xsize, ysize, raster_xsize, raster_ysize, buf_radius, gt, **kwargs):
    np.round_(np.clip(np.max(in_ar, axis = 0),0,255), out = out_ar)
]]>
    </PixelFunctionCode>
    <ColorInterp>Gray</ColorInterp>
    <SimpleSource>...</SimpleSource>
    ...
  </VRTRasterBand>
</VRTDataset>