首先看文檔：

usage: im2rec.py [-h] [--list] [--exts EXTS [EXTS ...]] [--chunks CHUNKS]
                 [--train-ratio TRAIN_RATIO] [--test-ratio TEST_RATIO]
                 [--recursive] [--no-shuffle] [--pass-through]
                 [--resize RESIZE] [--center-crop] [--quality QUALITY]
                 [--num-thread NUM_THREAD] [--color {-1,0,1}]
                 [--encoding {.jpg,.png}] [--pack-label]
                 prefix root

Create an image list or make a record database by reading from an image list

positional arguments:
  prefix                prefix of input/output lst and rec files.
  root                  path to folder containing images.

optional arguments:
  -h, --help            show this help message and exit

Options for creating image lists:
  --list                If this is set im2rec will create image list(s) by
                        traversing root folder and output to <prefix>.lst.
                        Otherwise im2rec will read <prefix>.lst and create a
                        database at <prefix>.rec (default: False)
  --exts EXTS [EXTS ...]
                        list of acceptable image extensions. (default:
                        [‘.jpeg‘, ‘.jpg‘, ‘.png‘])
  --chunks CHUNKS       number of chunks. (default: 1)
  --train-ratio TRAIN_RATIO
                        Ratio of images to use for training. (default: 1.0)
  --test-ratio TEST_RATIO
                        Ratio of images to use for testing. (default: 0)
  --recursive           If true recursively walk through subdirs and assign an
                        unique label to images in each folder. Otherwise only
                        include images in the root folder and give them label
                        0. (default: False)
  --no-shuffle          If this is passed, im2rec will not randomize the image
                        order in <prefix>.lst (default: True)

Options for creating database:
  --pass-through        whether to skip transformation and save image as is
                        (default: False)
  --resize RESIZE       resize the shorter edge of image to the newsize,
                        original images will be packed by default. (default:
                        0)
  --center-crop         specify whether to crop the center image to make it
                        rectangular. (default: False)
  --quality QUALITY     JPEG quality for encoding, 1-100; or PNG compression
                        for encoding, 1-9 (default: 95)
  --num-thread NUM_THREAD
                        number of thread to use for encoding. order of images
                        will be different from the input list if >1. the input
                        list will be modified to match the resulting order.
                        (default: 1)
  --color {-1,0,1}      specify the color mode of the loaded image. 1: Loads a
                        color image. Any transparency of image will be
                        neglected. It is the default flag. 0: Loads image in
                        grayscale mode. -1:Loads image as such including alpha
                        channel. (default: 1)
  --encoding {.jpg,.png}
                        specify the encoding of the images. (default: .jpg)
  --pack-label          Whether to also pack multi dimensional label in the
                        record file (default: False)

必須要填寫的參數有prefix、和root兩個路徑參數，

prefix：生成文件文件夾目錄

　　　 可以指定為.lst的路徑，這樣生成文件會和.lst同一級別，且會根據.lst中的條目生成二進制文件

root：圖片文件目錄，默認的話裏面是類別文件夾，類別名做label，每個文件夾存儲圖像

如果指定了.lst，則每個圖片路徑變為root路徑+.lst中每個圖片的路徑

--pack-label：在指定了.lst後很有用，此時允許label為高維度（主要是label可以設置為數組）

實際上我們之前也介紹過，.lst文件並不是必須的，僅有.rec和.idx就可以滿足需要（標簽存儲在.rec中），它是一個輔助（人工生成.lst指導.rec生成），或者作為一個結果展示（自動生成.rec時選擇同時生成.lst）。

『MXNet』im2rec腳本使用（待續）