I have a list of (.TIFF) files which I am renaming and saving in the same format. I am using cv2 module to do this.
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)
Why are the file sizes reduced from the original TIFF file? I haven't done any processing and visually the images look the same. But I am wondering, why the difference?
There could be many explanations of why the size of a TIFF file changes. Here are a few:
one file may be RGB with 3 bytes of red, green and blue per pixel, while another encoder may see that the file has fewer than 256 colours and decide to write a single byte of palette index per pixel (and store the 256 colours in a separate palette) rather than 3 bytes of RGB.
one file may be 8-bit, the other may be 1-bit (bi-level), 16 bit, 32-bit or 64-bit.
the files may have different compression - varying through none, to LZW, RLE or more recently JPEG.
one coder may have written IPTC or other metadata, whilst the other discarded it.
one coder may have included a low resolution preview, the other not.
In order to check, you could use exiftool which is just a Perl script and simple and small to install:
exiftool image.tif
Sample Output
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
Or tiffinfo which comes with libtiff and is also pretty small and easy to install:
tiffinfo image.tif
Sample Output
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)
Or ImageMagick which is installed on most Linux distros and is available for macOS and Windows - but is quite a large install:
magick identify -verbose image.tif
Sample Output
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
来源：https://stackoverflow.com/questions/53630689/opencv-why-does-the-file-size-change-when-i-read-and-write-an-image-without-mak