How to read minimum and maximum pixel values of an image in earth engine?

Question

I want to read the minimum and maximum rainfall value for my study region. While using the reducer function I can read the mean value, however, for min and max value it is showing null. I wish to extract the min and max value to control the color bar/ palette limit. How to read the min and max values. Below is my script,

Map.addLayer(Tawi, visParams, nameLayer, shown, opacity); /Tawi is the name of shapefile
Map.centerObject(Tawi);

var ChirpsDataset = ee.ImageCollection('UCSB-CHG/CHIRPS/DAILY');
var Chirps = ChirpsDataset.filterDate('2018-07-14', '2019-07-30').sum().clip(Tawi);
                     
print(Chirps, 'Precipitation');
var precip = Chirps.select('precipitation');

var meanValue = Chirps.reduceRegion({
  reducer: ee.Reducer.mean(),
  geometry: Tawi.geometry(),
  crs: 'EPSG:4326',
  crsTransform: [1,0,0,0,1,0],
  maxPixels: 1e9
});    
print('Mean precipitation:', meanValue)

var maxValue = Chirps.reduceRegion({
  reducer: ee.Reducer.max(),
  geometry: Tawi.geometry(),
  crs: 'EPSG:4326',
  crsTransform: [1,0,0,0,1,0],
  maxPixels: 1e9
});    
print('Max precipitation:', maxValue)

Here is the link to script.

Answer 1

You'd probably best define an appropriate scale for your analysis. Read about scale here. The composite image of you has crsTransform: [1,0,0,0,1,0], which gives a scale of 111319m:

print(precip.projection().nominalScale())

Probably, you want to run the computation on the scale of the imagery. It depends on where you are on the world, but approx 5km should fit well for your area. Thus, a better idea would be defining the scale (in meters), for example:

var maxValue = Chirps.reduceRegion({
  reducer: ee.Reducer.max(),
  geometry: Tawi.geometry(),
  scale: 5000,
  maxPixels: 1e9
});    
print('Max precipitation:', maxValue)