16位遥感图像转8位显示 %2线性拉伸

import cv2import gdalimport 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,maxdef 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 imgdef 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_nirBandfileName='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)