Pillow：JPEG压缩TIFF的质量控制和二次采样

Question

我正在用枕头创建多页的tiff。我想用JPEG压缩图层，我看到我可以用压缩选项:https://pillow.readthedocs.io/en/stable/handbook/image-file-formats.html#saving-tiff-images

多谢了。

Answer 1

我做了一些实验：

from PIL import Image
import numpy as np
import PIL.TiffImagePlugin as tiff

# Turn on debugging for some insights
TiffImagePlugin.DEBUG = True

# Create Numpy random image and make PIL Image from it
randImage= np.random.randint(0,256,(480,640,3), dtype=np.uint8)
i = Image.fromarray(randImage)

# Save with JPEG compression and file is smaller and "tiffdump" agrees it is JPEG encoded
# NOTE: It is "jpeg", not "tiff_jpeg" like the docs say
i.save("result.tif",compression="jpeg")

# Try and modify settings
import PIL.TiffImagePlugin as tiff

# Set some tags and see if they are saved
ifd=tiff.ImageFileDirectory_v2()
ifd[315]="Funky 315"
ifd[316]="Funky 316"

# I tried setting the YCbCrChromaSubSampling here but it makes no difference - maybe I did it wrong!
# It gets reported differently from how I expect when examined with "tiffdump"
# ifd[530]=0x10001

i.save("result.tif",compression="jpeg",tiffinfo=ifd)  

使用tiffdump检查：

tiffdump result.tif

Magic: 0x4949 <little-endian> Version: 0x2a <ClassicTIFF>
Directory 0: offset 511960 (0x7cfd8) next 0 (0)
ImageWidth (256) SHORT (3) 1<640>
ImageLength (257) SHORT (3) 1<480>
BitsPerSample (258) SHORT (3) 3<8 8 8>
Compression (259) SHORT (3) 1<7>        <--- New style JPEG
Photometric (262) SHORT (3) 1<2>
StripOffsets (273) LONG (4) 1<8>
SamplesPerPixel (277) SHORT (3) 1<3>
RowsPerStrip (278) SHORT (3) 1<480>
StripByteCounts (279) LONG (4) 1<511951>
PlanarConfig (284) SHORT (3) 1<1>
Artist (315) ASCII (2) 10<Funky 315\0>           <--- gets saved
HostComputer (316) ASCII (2) 10<Funky 316\0>     <--- gets saved
JPEGTables (347) UNDEFINED (7) 289<0xff 0xd8 0xff 0xdb 00 0x43 00 0x8 0x6 0x6 0x7 0x6 0x5 0x8 0x7 0x7 0x7 0x9 0x9 0x8 0xa 0xc 0x14 0xd ...>