16位遥感图像转8位显示 %2线性拉伸

import cv2
import gdal
import numpy as np

#计算2% 98%处值作为最小 最大值
def minmaximg(width,heigh,img):
    img_fla = img.flatten() #展成一维数组
    #img_fla = np.sort(img_fla) #排序
    len=img.max()
    print('max=%d' % len)
    num=np.zeros(len+1,dtype=np.int32)
    print('size=%d'%np.size(img_fla))
    for i in np.arange(np.size(img_fla)):
        num[img_fla[i]]=num[img_fla[i]]+1
        #print('img_fla= %d,%d'%(i,img_fla[i]))
        #print('num %d,%d' % (i, num[img_fla[i]]))
    p=0
    min=0
    max=0
    print(np.sum(num))
    for j in np.arange(len+1):
        p = num[j] / (width*heigh) + p
        #print('/n',num[j])
        if p>=0.02:
            min=j
            break
    p=0

    for j in np.arange(len+1):
        p = num[j] / (width * heigh) + p
        # print('/n,%', num[j])
        # print('/n,%', p)
        # print('/n,%', j)
        if p >= 0.98:
            max = j
            break
    return min,max

def linearstretching(img,min,max):

    img=np.where(img > min, img, min)
    img=np.where(img < max, img, max)
    img = (img - min) / (max - min) * 255
    return img

def readTif(fileName):
    dataset = gdal.Open(fileName)
    if dataset == None:
        print(fileName+"掩膜失败，文件无法打开")
        return
    im_width = dataset.RasterXSize #栅格矩阵的列数
    im_height = dataset.RasterYSize #栅格矩阵的行数
    im_bands = dataset.RasterCount #波段数
    im_data = dataset.ReadAsArray(0,0,im_width,im_height)#获取数据
    im_geotrans = dataset.GetGeoTransform()#获取仿射矩阵信息
    im_proj = dataset.GetProjection()#获取投影信息
    im_blueBand =  im_data[0,0:im_height,0:im_width]#获取蓝波段
    im_greenBand = im_data[1,0:im_height,0:im_width]#获取绿波段
    im_redBand =   im_data[2,0:im_height,0:im_width]#获取红波段
    im_nirBand = im_data[3,0:im_height,0:im_width]#获取近红外波段
    return im_width,im_height,im_bands,im_blueBand,im_greenBand,im_redBand,im_nirBand

fileName='E:\SHIP\GF1_PMS1_E107.5_N10.4_20150313_L1A0000693445-MSS1.tiff'
im_width,im_height,im_bands,im_blueBand,im_greenBand,im_redBand,im_nirBand = \
readTif(fileName)

bmin,bmax = minmaximg(im_width,im_height,im_blueBand)
gmin,gmax = minmaximg(im_width,im_height,im_greenBand)
rmin,rmax = minmaximg(im_width,im_height,im_redBand)

im_blueBand=linearstretching(im_blueBand,bmin,bmax)
im_greenBand=linearstretching(im_greenBand,gmin,gmax)
im_redBand=linearstretching(im_redBand,rmin,rmax)

img=cv2.merge([im_blueBand,im_greenBand,im_redBand])
cv2.imwrite('GF1_PMS1_E107.5_N10.4_20150313_L1A0000693445-MSS1.jpg',img)