如何使用二进制字符串中的Wand创建高分辨率JPEG

我正在尝试使用imagemagick将一些PDF转换为高分辨率jpegs.我正在努力赢得10,64的python 3.62 – 64位和魔杖0.4.4.在命令行我有：

$/e/ImageMagick-6.9.9-Q16-HDRI/convert.exe -density 400 myfile.pdf -scale 2000x1000 test3.jpg.

这对我很有用.

在python中：

from wand.image import Image

file_path = os.path.dirname(os.path.abspath(__file__))+os.sep+"myfile.pdf"

with Image(filename=file_path, resolution=400) as image:
    image.save()
    image_jpeg = image.convert('jpeg')

这给了我低分辨率的JPEG.我如何将其转换为我的魔杖代码来做同样的事情？

编辑：

我意识到问题是输入pdf必须作为二进制字符串读入Image对象,所以基于http://docs.wand-py.org/en/0.4.4/guide/read.html#read-blob我试过：

with open(file_path,'rb') as f:
    image_binary = f.read()

f.close()

with Image(blob=image_binary,resolution=400) as img:
    img.transform('2000x1000', '100%')
    img.make_blob('jpeg')
    img.save(filename='out.jpg')

这在ok中读取文件,但输出被分成10个文件.为什么？我需要把它变成1个高分辨率的jpeg.

编辑：

我需要将jpeg发送到OCR api,所以我想知道是否可以将输出写入像object这样的文件.看着https://www.imagemagick.org/api/magick-image.php#MagickWriteImageFile,我试过：

emptyFile =  Image(width=1500, height=2000)

with Image(filename=file_path, resolution=400) as image:

    library.MagickResetIterator(image.wand)
    # Call C-API Append method.
    resource_pointer = library.MagickAppendImages(image.wand,
                                                  True)

    library.MagickWriteImagesFile(resource_pointer,emptyFile)

这给出了：

 File "E:/ENVS/r3/pdfminer.six/ocr_space.py", line 113, in <module>
test_file = ocr_stream(filename='test4.jpg')
 File "E:/ENVS/r3/pdfminer.six/ocr_space.py", line 96, in ocr_stream
library.MagickWriteImagesFile(resource_pointer,emptyFile)
ctypes.ArgumentError: argument 2: <class 'TypeError'>: wrong type

我怎样才能使这个工作？

解决方法:

Why? I need to get this into 1 high res jpeg.

PDF包含ImageMagick在“堆栈”中考虑单个图像的页面. wand库提供了一个wand.image.Image.sequance来处理每个页面.

但是,要将所有图像附加到单个JPEG中.你可以迭代每一页&将它们拼接在一起,或者调用C-API的方法MagickAppendImages.

from wand.image import Image
from wand.api import library
import ctypes

# Map C-API not provided by wand library.
library.MagickAppendImages.argtypes = [ctypes.c_void_p, ctypes.c_int]
library.MagickAppendImages.restype = ctypes.c_void_p

with Image(filename="path_to_document.pdf", resolution=400) as image:
    # Do all your preprocessing first
    # Ether word directly on the wand instance, or iterate over each page.
    # ...
    # To write all "pages" into a single image.
    # Reset the stack iterator.
    library.MagickResetIterator(image.wand)                    
    # Call C-API Append method.
    resource_pointer = library.MagickAppendImages(image.wand,
                                                  True)        
    # Write C resource directly to disk.
    library.MagickWriteImages(resource_pointer,                
                              "output.jpeg".encode("ASCII"),
                              False)

更新：

I need to send the jpeg to an OCR api …

假设您使用OpenCV的python API,您只需要迭代每个页面,并通过numpy缓冲区将图像文件数据传递给OCR.

from wand.image import Image
import numpy
import cv2

def ocr_process(file_data_buffer):
     """ Replace with whatever your OCR-API calls for """
     mat_instance = cv2.imdecode(file_data_buffer)
     # ... work ...

source_image="path_to_document.pdf"
with Image(filename=source_image, resolution=400) as img:
    for page in img.sequence:
        file_buffer = numpy.asarray(bytearray(page.make_blob("JPEG")),
                                    dtype=numpy.uint8)
        ocr_process(file_buffer)

so I was wondering if I could write the output to a file like object

不要假设来自不同库的python“图像”对象(或下划线C结构)彼此相当.

在不知道OCR api的情况下,我无法帮助你超越wand部分,但我可以建议以下其中一个……

>使用临时中间文件. (较慢的I / O,但更容易学习/开发/调试)

with Image(filename=INPUT_PATH) as img:
    # work
    img.save(filename=OUTPUT_PATH)
# OCR work on OUTPUT_PATH

>如果OCR API支持,请使用文件描述符. (与上述相同)

with open(INPUT_PATH, 'rb') as fd:
    with Image(file=fd) as img:
        # work
        # OCR work ???

>使用blob. (更快的I / O但需要更多的内存)

buffer = None
with Image(filename=INPUT_PATH) as img:
    # work
    buffer = img.make_blob(FORMAT)
if buffer:
    # OCR work ???

更多更新

将所有评论结合在一起,解决方案可能是……

from wand.image import Image
from wand.api import library
import ctypes
import requests

# Map C-API not provided by wand library.
library.MagickAppendImages.argtypes = [ctypes.c_void_p, ctypes.c_int]
library.MagickAppendImages.restype = ctypes.c_void_p

with Image(filename='path_to_document.pdf', resolution=400) as image:
    # ... Do pre-processing ...
    # Reset the stack iterator.
    library.MagickResetIterator(image.wand)
    # Call C-API Append method.
    resource_pointer = library.MagickAppendImages(image.wand, True)
    # Convert to JPEG.
    library.MagickSetImageFormat(resource_pointer, b'JPEG')
    # Create size sentinel.
    length = ctypes.c_size_t()
    # Write image blob to memory.
    image_data_pointer = library.MagickGetImagesBlob(resource_pointer,
                                                     ctypes.byref(length))
    # Ensure success
    if image_data_pointer and length.value:
        # Create buffer from memory address
        payload = ctypes.string_at(image_data_pointer, length.value)
        # Define local filename.
        payload_filename = 'my_hires_image.jpg'
        # Post payload as multipart encoded image file with filename.
        requests.post(THE_URL, files={'file': (payload_filename, payload)})

标签：python,imagemagick,wand,wand,wand
来源： https://codeday.me/bug/20190622/1263570.html