如何通过Python读取16位或32位图像并将正确的图像值作为数组获取?
我尝试使用PIL + Numpy和GDAL + Numpy等方法读取SRTM(航天飞机雷达地形测量)数据。我只需要一小部分,所以我使用ArcGIS将所需范围作为tif文件导出。
然而,经过上述测试之后,数组中的值是不正确的。例如,我使用了一个高程范围从136到737的加州SRTM数据,但是当我使用numpy获取最大和最小值时,数组值的范围是从-3.40到737,并且出现了许多负值。我该怎么办?是否犯了一些错误?
我在ipython中使用的代码如下:
import Image
import numpy as num
im=Image.open('srtm.tif')
imarray=num.array(im)
imarray
array([[ -3.40282347e+38, -3.40282347e+38, 4.00000000e+02, ...,
0.00000000e+00, 0.00000000e+00, 0.00000000e+00],
[ -3.40282347e+38, -3.40282347e+38, 4.00000000e+02, ...,
0.00000000e+00, 0.00000000e+00, 0.00000000e+00],
[ -3.40282347e+38, -3.40282347e+38, 4.00000000e+02, ...,
0.00000000e+00, 0.00000000e+00, 0.00000000e+00],
...,
[ 0.00000000e+00, 0.00000000e+00, 0.00000000e+00, ...,
0.00000000e+00, 0.00000000e+00, 0.00000000e+00],
[ 0.00000000e+00, 0.00000000e+00, 0.00000000e+00, ...,
0.00000000e+00, 0.00000000e+00, 0.00000000e+00],
[ 0.00000000e+00, 0.00000000e+00, 0.00000000e+00, ...,
0.00000000e+00, 0.00000000e+00, 0.00000000e+00]], dtype=float32)
import gdal
tif = gdal.Open('srtm.tif')
arr = tif.ReadAsArray()
arr
array([[ -3.40282347e+38, -3.40282347e+38, 4.00000000e+02, ...,
-3.40282347e+38, -3.40282347e+38, -3.40282347e+38],
[ -3.40282347e+38, -3.40282347e+38, 4.00000000e+02, ...,
6.11000000e+02, 6.17000000e+02, 6.17000000e+02],
[ -3.40282347e+38, -3.40282347e+38, 4.00000000e+02, ...,
6.11000000e+02, 6.17000000e+02, 6.17000000e+02],
...,
[ 1.50000000e+02, 1.50000000e+02, 1.48000000e+02, ...,
1.73000000e+02, 1.73000000e+02, 1.73000000e+02],
[ 1.49000000e+02, 1.49000000e+02, 1.48000000e+02, ...,
1.73000000e+02, 1.73000000e+02, 1.73000000e+02],
[ 1.49000000e+02, 1.49000000e+02, 1.48000000e+02, ...,
1.73000000e+02, 1.73000000e+02, 1.73000000e+02]], dtype=float32)
num.max(arr)
737.0
num.min(arr)
-3.4028235e+38