Discrepancy when counting pixels in Google Earth Engine Python API

Question

I have this polygon:

ee.Geometry({
  "functionInvocationValue": {
    "functionName": "GeometryConstructors.Polygon",
    "arguments": {
      "coordinates": {
        "constantValue": [
          [
            [
              39.395406,
              49.043902
            ],
            [
              39.395406,
              49.046139
            ],
            [
              39.399011,
              49.046139
            ],
            [
              39.399011,
              49.043902
            ],
            [
              39.395406,
              49.043902
            ]
          ]
        ]
      },
      "evenOdd": {
        "constantValue": true
      }
    }
  }
})

I would like to get the value in Sentinel-2 band 4 for all the pixels.

This is the code I'm using:

start_date,end_date = '2022-08-05','2022-08-07'
bands = ['B4']
sensor = "COPERNICUS/S2_SR_HARMONIZED"

img_collection = (ee.ImageCollection(sensor).filterBounds(polygon).filterDate(start_date,end_date).select(bands))
pixels_info = img_collection.getRegion(geometry=polygon, scale=10)
df = pd.DataFrame(pixels_info.getInfo())
df.columns = df.iloc[0]
df = df.drop(0)
df.shape

>>> (1000, 5)

This means there are 1000 pixels for a specific date (2022-08-06).

However, when I directly count the pixels, I get a different number:

img_id = 'COPERNICUS/S2_SR_HARMONIZED/20220806T082611_20220806T083525_T37UEQ'
image = ee.Image(img_id)
t_pixel_count = image.select(['B4']).reduceRegion(reducer=ee.Reducer.count(),geometry=polygon,scale=10).rename(['B4'],['total_pixels'])
t_pixel_count.getInfo()

>>> {'total_pixels': 666}

Why is that? and how many pixels there are in the image?

Answer 1

After some consultation, I realized that I also needed to specify the CRS (in the getRegion function), because the scale was not enough.

Now it outputs the same number of pixels:

start_date,end_date = '2022-08-05','2022-08-07'
bands = ['B4']
sensor = "COPERNICUS/S2_SR_HARMONIZED"

img_collection = (ee.ImageCollection(sensor).filterBounds(polygon).filterDate(start_date,end_date).select(bands))
pixels_info = img_collection.getRegion(geometry=polygon, scale=10,crs='EPSG:32637')
df = pd.DataFrame(pixels_info.getInfo())
df.columns = df.iloc[0]
df = df.drop(0)
df.shape

>>> (664, 5)

This means there are 1000 pixels for a specific date (2022-08-06).

However, when I directly count the pixels, I get a different number:

img_id = 'COPERNICUS/S2_SR_HARMONIZED/20220806T082611_20220806T083525_T37UEQ'
image = ee.Image(img_id)
t_pixel_count = image.select(['B4']).reduceRegion(reducer=ee.Reducer.count(),geometry=polygon,scale=10, crs='EPSG:32637').rename(['B4'],['total_pixels'])
t_pixel_count.getInfo()

>>> {'total_pixels': 664}