Saving an Image stored in BytesIO in pillow

问题

I have an image stored as BytesIO of Pillow and I need to save it to a file with some header information (containing textual attributes) that I need to add specific to my problem. I need the bytes to be represented according to some image compression format. Would that be possible? If yes, how it can be done? I also need to store more than one image in the file.

回答1:

Storing more than one image in a file is problematic for PNG, JPEG and the most of the common formats. One option for that is TIFF - not sure if that works for you?

Here's how you can store some additional text in a PNG at least:

#!/usr/bin/env python3

from PIL.PngImagePlugin import Image, PngInfo

# Create empty metadata and add a couple of text strings
metadata = PngInfo()
metadata.add_text("Key1:","Value1")
metadata.add_text("Key2:","Value2")

# Create red image and save with metadata embedded
im = Image.new('RGB',(64,64),'red')
im.save("result.png", pnginfo=metadata)

If you check that with pngcheck you will see:

pngcheck -7v result.png

Sample Output

File: result.png (200 bytes)
  chunk IHDR at offset 0x0000c, length 13
    64 x 64 image, 24-bit RGB, non-interlaced
  chunk tEXt at offset 0x00025, length 12, keyword: Key1:
    Value1
  chunk tEXt at offset 0x0003d, length 12, keyword: Key2:
    Value2
  chunk IDAT at offset 0x00055, length 95
    zlib: deflated, 32K window, default compression
  chunk IEND at offset 0x000c0, length 0
No errors detected in result.png (5 chunks, 98.4% compression).

Here's how to save 3 images and a comment in a single TIFF file:

from PIL import Image 
from PIL.TiffImagePlugin import ImageFileDirectory_v2, TiffTags 

# Create a structure to hold meta-data
ifd = ImageFileDirectory_v2() 
ifd[270] = 'Some Funky Comment' 
ifd.tagtype[270] = TiffTags.ASCII 

# Create red image and save with metadata embedded 
im1 = Image.new('RGB',(50,50),'red') 
im2 = Image.new('RGB',(64,64),'green') 
im3 = Image.new('RGB',(80,80),'blue') 
im1.save("result.tif", append_images[im2,im3], save_all=True, tiffinfo=ifd)

And check that with:

tiffinfo -v result.tif

Sample Output

TIFF Directory at offset 0x8 (8)
  Image Width: 50 Image Length: 50
  Bits/Sample: 8
  Compression Scheme: None
  Photometric Interpretation: RGB color
  Samples/Pixel: 3
  Rows/Strip: 50
  Planar Configuration: single image plane
  ImageDescription: Some Funky Comment
TIFF Directory at offset 0x1e08 (7688)
  Image Width: 64 Image Length: 64
  Bits/Sample: 8
  Compression Scheme: None
  Photometric Interpretation: RGB color
  Samples/Pixel: 3
  Rows/Strip: 64
  Planar Configuration: single image plane
  ImageDescription: Some Funky Comment
TIFF Directory at offset 0x4eb8 (20152)
  Image Width: 80 Image Length: 80
  Bits/Sample: 8
  Compression Scheme: None
  Photometric Interpretation: RGB color
  Samples/Pixel: 3
  Rows/Strip: 80
  Planar Configuration: single image plane
  ImageDescription: Some Funky Comment

You can then extract the images on the command-line with ImageMagick like this.

To extract first image:

magick result.tif[0] first.png

To extract last image:

magick result.tif[-1] last.png

To extract all three images:

magick result.tif image-%d.png

Result

-rw-r--r--  1 mark  staff  457 21 Jan 08:11 image-0.png
-rw-r--r--  1 mark  staff  458 21 Jan 08:11 image-1.png
-rw-r--r--  1 mark  staff  460 21 Jan 08:11 image-2.png

Note: Use convert in place of magick above if you are running v6 ImageMagick.

Keywords: Python, PIL, image processing, multiple images, TIF, comment, tiffinfo, IFD, PNG tEXt.

来源：https://stackoverflow.com/questions/59827421/saving-an-image-stored-in-bytesio-in-pillow

标签

python-imaging-library

image-compression