Pyvips rounding my resolution

Question

I am working with pyvips to test some cropping speeds vs. other packages. I need to access my x and y resolution. I am able to, but for some reason pyvips is rounding to the nearest mm. I opened my TIFF in QGIS and the resolution is 0.009330691929342804433,-0.009330691929342804433. I am unsure how to capture this number using pyvips.

img = pyvips.Image.new_from_file(ortho, access='sequential')
print(img.xres)
print(img.yres)

output:
1.0 -type='float'
1.0 - type='float'

Edits

Link to get sample image

Using pyvips 8.12

QGIS Image:

EDITS After @jcupitt answer:

from PIL import Image
from PIL.TiffTags import TAGS

with Image.open('image.tif') as img:
    meta_dict = {TAGS[key] : img.tag[key] for key in img.tag.keys()}
print(meta_dict)

Output:
...'ModelPixelScaleTag': (0.009330691929340133, 0.009330691929339859, 0.0)

Edits After @jcupitt Edits:

Used exifread, values are also in there:

import exifread

f = open('image.tif', 'rb')
tags = exifread.process_file(f)
for tag in tags.keys():
    if tag not in ('JPEGThumbnail', 'TIFFThumbnail', 'Filename', 'EXIF MakerNote'):
        print("Key: %s, value %s" % (tag, tags[tag]))

Output:

Key: Image ImageWidth, value 3564
Key: Image ImageLength, value 2640
Key: Image BitsPerSample, value [8, 8, 8, 8]
Key: Image Compression, value Uncompressed
Key: Image PhotometricInterpretation, value 2
Key: Image StripOffsets, value []
Key: Image SamplesPerPixel, value 4
Key: Image RowsPerStrip, value 1
Key: Image StripByteCounts, value []
Key: Image PlanarConfiguration, value 1
Key: Image ExtraSamples, value Unassociated Alpha
Key: Image SampleFormat, value UnsignedUnsignedUnsignedUnsigned
Key: Image Tag 0x830E, value [(0.009330691929340133,), (0.009330691929339859,), (0.0,)]
Key: Image Tag 0x8482, value [(0.0,), (0.0,), (0.0,), (-13646305.785530405,), (5497215.247385725,), (0.0,)]
Key: Image Tag 0x87AF, value [1, 1, 0, 7, 1024, 0, 1, 1, 1025, 0, 1, 1, 1026, 34737, 25, 0, 2049, 34737, 7, 25, 2054, 0, 1, 9102, 3072, 0, 1, 3857, 3076, 0, 1, 9001]
Key: Image Tag 0x87B1, value WGS 84 / Pseudo-Mercator|WGS 84|
Key: Image Tag 0xA480, value <GDALMetadata>
  <Item name="acquisitionEndDate">2021-10-08T20:43:00+00:00</Item>
  <Item name="acquisitionStartDate">2021-10-08T20:13:00+00:00</Item>
  <Item name="isCalibrated">False</Item>
</GDALMetadata>

Answer 1

The sample image you linked has none of the standard libtiff resolution tags. Here's what you see with tiffinfo (exiftool is similar):

$ tiffinfo image.tif 
TIFFReadDirectory: Warning, Unknown field with tag 33550 (0x830e) encountered.
TIFFReadDirectory: Warning, Unknown field with tag 33922 (0x8482) encountered.
TIFFReadDirectory: Warning, Unknown field with tag 34735 (0x87af) encountered.
TIFFReadDirectory: Warning, Unknown field with tag 34737 (0x87b1) encountered.
TIFFReadDirectory: Warning, Unknown field with tag 42112 (0xa480) encountered.
TIFF Directory at offset 0x8 (8)
  Image Width: 3564 Image Length: 2640
  Bits/Sample: 8
  Sample Format: unsigned integer
  Compression Scheme: None
  Photometric Interpretation: RGB color
  Extra Samples: 1<unassoc-alpha>
  Samples/Pixel: 4
  Rows/Strip: 1
  Planar Configuration: single image plane
  Tag 33550: 0.009331,0.009331,0.000000
  Tag 33922: 0.000000,0.000000,0.000000,-13646305.785530,5497215.247386,0.000000
  Tag 34735: 1,1,0,7,1024,0,1,1,1025,0,1,1,1026,34737,25,0,2049,34737,7,25,2054,0,1,9102,3072,0,1,3857,3076,0,1,9001
  Tag 34737: WGS 84 / Pseudo-Mercator|WGS 84|
  Tag 42112: <GDALMetadata>
  <Item name="acquisitionEndDate">2021-10-08T20:43:00+00:00</Item>
  <Item name="acquisitionStartDate">2021-10-08T20:13:00+00:00</Item>
  <Item name="isCalibrated">False</Item>
</GDALMetadata>

You can see the resolution (I suppose?) in the unofficial tag 33550. libvips currently has no way of reading these extra, undocumented tags, so you're out of luck.

Are you cropping many small tiles to feed to an ML system? You'll probably find fetch is quicker than crop. Have a look at:

https://github.com/libvips/pyvips/issues/100#issuecomment-493960943