Python Opencv：当我读写一个图像而不做任何更改时，为什么文件大小会改变？_Python_Opencv_Glob_Tiff_Filesize

Python Opencv：当我读写一个图像而不做任何更改时，为什么文件大小会改变？

python opencv

Python Opencv：当我读写一个图像而不做任何更改时，为什么文件大小会改变？,python,opencv,glob,tiff,filesize,Python,Opencv,Glob,Tiff,Filesize,我有一个（.TIFF）文件列表，我正在重命名这些文件并以相同的格式保存它们。我使用cv2模块来实现这一点 import cv2 import os import glob os.chdir('C:/99_Temp/') for file in glob.glob("*.tiff"): f = os.path.splitext(file) time_val = f[0][:2] a1 = cv2.imread(file) cv2.imwrite(time_val+'.

我有一个（.TIFF）文件列表，我正在重命名这些文件并以相同的格式保存它们。我使用cv2模块来实现这一点

import cv2
import os
import glob

os.chdir('C:/99_Temp/')

for file in glob.glob("*.tiff"):
   f = os.path.splitext(file)
   time_val = f[0][:2]
   a1 = cv2.imread(file)
   cv2.imwrite(time_val+'.tiff',a1)

为什么文件大小要比原始TIFF文件小？我没有做任何处理，图像在视觉上看起来是一样的。但我想知道，为什么会有不同

关于TIFF文件大小变化的原因，可能有很多解释。以下是一些：

一个文件可能是RGB，每个像素有3个字节的红色、绿色和蓝色，而另一个编码器可能看到该文件的颜色少于256种，并决定每像素写入一个字节的调色板索引（并将256种颜色存储在单独的调色板中），而不是3个字节的RGB
一个文件可以是8位，另一个文件可以是1位（双电平）、16位、32位或64位
这些文件可能有不同的压缩-从none到LZW、RLE或最近的JPEG都有所不同
一个编码者可能编写了IPTC或其他元数据，而另一个编码者则丢弃了它
一个编码器可能包含低分辨率预览，另一个则没有

为了进行检查，您可以使用

exiftool

，它只是一个Perl脚本，安装起来简单小巧：

exiftool image.tif

tiffinfo image.tif

样本输出

ExifTool Version Number         : 11.11
File Name                       : image.tif
Directory                       : .
File Size                       : 91 kB
File Modification Date/Time     : 2018:11:28 09:38:03+00:00
File Access Date/Time           : 2018:12:05 13:15:15+00:00
File Inode Change Date/Time     : 2018:12:05 13:15:10+00:00
File Permissions                : rw-r--r--
File Type                       : TIFF
File Type Extension             : tif
MIME Type                       : image/tiff
Exif Byte Order                 : Little-endian (Intel, II)
Image Width                     : 784
Image Height                    : 1466
Bits Per Sample                 : 8
Compression                     : LZW
Photometric Interpretation      : BlackIsZero
Strip Offsets                   : (Binary data 827 bytes, use -b option to extract)
Samples Per Pixel               : 1
Rows Per Strip                  : 10
Strip Byte Counts               : (Binary data 642 bytes, use -b option to extract)
Planar Configuration            : Chunky
Predictor                       : Horizontal differencing
Image Size                      : 784x1466
Megapixels                      : 1.1

TIFF Directory at offset 0x16894 (92308)
  Image Width: 784 Image Length: 1466
  Bits/Sample: 8
  Compression Scheme: LZW
  Photometric Interpretation: min-is-black
  Samples/Pixel: 1
  Rows/Strip: 10
  Planar Configuration: single image plane
  Predictor: horizontal differencing 2 (0x2)

Image: image.tif
  Format: TIFF (Tagged Image File Format)
  Mime type: image/tiff
  Class: DirectClass
  Geometry: 784x1466+0+0
  Units: PixelsPerInch
  Colorspace: Gray
  Type: Grayscale
  Endianess: LSB
  Depth: 8-bit
  Channel depth:
    Gray: 8-bit
  Channel statistics:
    Pixels: 1149344
    Gray:
  ...
  ...
  Matte color: grey74
  Background color: white
  Border color: srgb(223,223,223)
  Transparent color: none
  Interlace: None
  Intensity: Undefined
  Compose: Over
  Page geometry: 784x1466+0+0
  Dispose: Undefined
  Iterations: 0
  Compression: LZW
  Orientation: TopLeft
  Properties:
    date:create: 2018-12-05T13:15:10+00:00
    date:modify: 2018-11-28T09:38:03+00:00
    signature: 5f9afdc8efd4757daa7f6bdba105f6ae149833c1c8103dd544f0073bb302069d
    tiff:alpha: unspecified
    tiff:endian: lsb
    tiff:photometric: min-is-black
    tiff:rows-per-strip: 10
  Artifacts:
    verbose: true
  Tainted: False
  Filesize: 93622B
  Number pixels: 1.14934M
  Pixels per second: 114.935MP
  User time: 0.010u
  Elapsed time: 0:01.009
  Version: ImageMagick 7.0.8-14 Q16 x86_64 2018-11-16 https://imagemagick.org

或者

tiffinfo

，它与

libtiff

一起提供，并且非常小，易于安装：

exiftool image.tif

tiffinfo image.tif

样本输出

ExifTool Version Number         : 11.11
File Name                       : image.tif
Directory                       : .
File Size                       : 91 kB
File Modification Date/Time     : 2018:11:28 09:38:03+00:00
File Access Date/Time           : 2018:12:05 13:15:15+00:00
File Inode Change Date/Time     : 2018:12:05 13:15:10+00:00
File Permissions                : rw-r--r--
File Type                       : TIFF
File Type Extension             : tif
MIME Type                       : image/tiff
Exif Byte Order                 : Little-endian (Intel, II)
Image Width                     : 784
Image Height                    : 1466
Bits Per Sample                 : 8
Compression                     : LZW
Photometric Interpretation      : BlackIsZero
Strip Offsets                   : (Binary data 827 bytes, use -b option to extract)
Samples Per Pixel               : 1
Rows Per Strip                  : 10
Strip Byte Counts               : (Binary data 642 bytes, use -b option to extract)
Planar Configuration            : Chunky
Predictor                       : Horizontal differencing
Image Size                      : 784x1466
Megapixels                      : 1.1

TIFF Directory at offset 0x16894 (92308)
  Image Width: 784 Image Length: 1466
  Bits/Sample: 8
  Compression Scheme: LZW
  Photometric Interpretation: min-is-black
  Samples/Pixel: 1
  Rows/Strip: 10
  Planar Configuration: single image plane
  Predictor: horizontal differencing 2 (0x2)

Image: image.tif
  Format: TIFF (Tagged Image File Format)
  Mime type: image/tiff
  Class: DirectClass
  Geometry: 784x1466+0+0
  Units: PixelsPerInch
  Colorspace: Gray
  Type: Grayscale
  Endianess: LSB
  Depth: 8-bit
  Channel depth:
    Gray: 8-bit
  Channel statistics:
    Pixels: 1149344
    Gray:
  ...
  ...
  Matte color: grey74
  Background color: white
  Border color: srgb(223,223,223)
  Transparent color: none
  Interlace: None
  Intensity: Undefined
  Compose: Over
  Page geometry: 784x1466+0+0
  Dispose: Undefined
  Iterations: 0
  Compression: LZW
  Orientation: TopLeft
  Properties:
    date:create: 2018-12-05T13:15:10+00:00
    date:modify: 2018-11-28T09:38:03+00:00
    signature: 5f9afdc8efd4757daa7f6bdba105f6ae149833c1c8103dd544f0073bb302069d
    tiff:alpha: unspecified
    tiff:endian: lsb
    tiff:photometric: min-is-black
    tiff:rows-per-strip: 10
  Artifacts:
    verbose: true
  Tainted: False
  Filesize: 93622B
  Number pixels: 1.14934M
  Pixels per second: 114.935MP
  User time: 0.010u
  Elapsed time: 0:01.009
  Version: ImageMagick 7.0.8-14 Q16 x86_64 2018-11-16 https://imagemagick.org

或ImageMagick，它安装在大多数Linux发行版上，可用于macOS和Windows，但安装量相当大：

magick identify -verbose image.tif

样本输出

ExifTool Version Number         : 11.11
File Name                       : image.tif
Directory                       : .
File Size                       : 91 kB
File Modification Date/Time     : 2018:11:28 09:38:03+00:00
File Access Date/Time           : 2018:12:05 13:15:15+00:00
File Inode Change Date/Time     : 2018:12:05 13:15:10+00:00
File Permissions                : rw-r--r--
File Type                       : TIFF
File Type Extension             : tif
MIME Type                       : image/tiff
Exif Byte Order                 : Little-endian (Intel, II)
Image Width                     : 784
Image Height                    : 1466
Bits Per Sample                 : 8
Compression                     : LZW
Photometric Interpretation      : BlackIsZero
Strip Offsets                   : (Binary data 827 bytes, use -b option to extract)
Samples Per Pixel               : 1
Rows Per Strip                  : 10
Strip Byte Counts               : (Binary data 642 bytes, use -b option to extract)
Planar Configuration            : Chunky
Predictor                       : Horizontal differencing
Image Size                      : 784x1466
Megapixels                      : 1.1

TIFF Directory at offset 0x16894 (92308)
  Image Width: 784 Image Length: 1466
  Bits/Sample: 8
  Compression Scheme: LZW
  Photometric Interpretation: min-is-black
  Samples/Pixel: 1
  Rows/Strip: 10
  Planar Configuration: single image plane
  Predictor: horizontal differencing 2 (0x2)

Image: image.tif
  Format: TIFF (Tagged Image File Format)
  Mime type: image/tiff
  Class: DirectClass
  Geometry: 784x1466+0+0
  Units: PixelsPerInch
  Colorspace: Gray
  Type: Grayscale
  Endianess: LSB
  Depth: 8-bit
  Channel depth:
    Gray: 8-bit
  Channel statistics:
    Pixels: 1149344
    Gray:
  ...
  ...
  Matte color: grey74
  Background color: white
  Border color: srgb(223,223,223)
  Transparent color: none
  Interlace: None
  Intensity: Undefined
  Compose: Over
  Page geometry: 784x1466+0+0
  Dispose: Undefined
  Iterations: 0
  Compression: LZW
  Orientation: TopLeft
  Properties:
    date:create: 2018-12-05T13:15:10+00:00
    date:modify: 2018-11-28T09:38:03+00:00
    signature: 5f9afdc8efd4757daa7f6bdba105f6ae149833c1c8103dd544f0073bb302069d
    tiff:alpha: unspecified
    tiff:endian: lsb
    tiff:photometric: min-is-black
    tiff:rows-per-strip: 10
  Artifacts:
    verbose: true
  Tainted: False
  Filesize: 93622B
  Number pixels: 1.14934M
  Pixels per second: 114.935MP
  User time: 0.010u
  Elapsed time: 0:01.009
  Version: ImageMagick 7.0.8-14 Q16 x86_64 2018-11-16 https://imagemagick.org

胡乱猜测：tiff编码的不同实现/版本/参数？原始文件是如何生成的？而且，如果您再次读写第二个图像，第二个和第三个图像的大小是否相同？