Convert .IMG (Classic Disk Image) to .PNG/.JPG in Python

Question

I have a dataset of 1,00,000+ .IMG files that I need to convert to .PNG / .JPG format to apply CNN for a simple classification task.
I referred to this answer and the solution works for me partially. What I mean is that some images are not properly converted. The reason for that, according to my understanding is that some images have a Pixel Depth of 16 while some have 8.

for file in fileList:
    rawData = open(file, 'rb').read()
    size = re.search("(LINES              = \d\d\d\d)|(LINES              = \d\d\d)", str(rawData))
    pixelDepth = re.search("(SAMPLE_BITS        = \d\d)|(SAMPLE_BITS        = \d)", str(rawData))
    size = (str(size)[-6:-2])
    pixelDepth = (str(pixelDepth)[-4:-2])
    print(int(size))
    print(int(pixelDepth))
    imgSize = (int(size), int(size))



    img = Image.frombytes('L', imgSize, rawData)
    img.save(str(file)+'.jpg')

Data Source: NASA Messenger Mission
.IMG files and their corresponding converted .JPG Files

---

Files with Pixel Depth of 8 are successfully converted:

---

Files with Pixel Depth of 16 are NOT properly converted:

Please let me know if there's any more information that I should provide.

Answer 1

Hopefully, from my other answer, here, you now have a better understanding of how your files are formatted. So, the code should look something like this:

#!/usr/bin/env python3

import sys
import re
import numpy as np
from PIL import Image
import cv2

rawData  = open('EW0220137564B.IMG', 'rb').read()
# File size in bytes
fs       = len(rawData)
bitDepth = int(re.search("SAMPLE_BITS\s+=\s+(\d+)",str(rawData)).group(1))
bytespp  = int(bitDepth/8)
height   = int(re.search("LINES\s+=\s+(\d+)",str(rawData)).group(1))
width    = int(re.search("LINE_SAMPLES\s+=\s+(\d+)",str(rawData)).group(1))
print(bitDepth,height,width)

# Offset from start of file to image data - assumes image at tail end of file
offset = fs - (width*height*bytespp)

# Check bitDepth
if bitDepth == 8:
    na = np.frombuffer(rawData, offset=offset, dtype=np.uint8).reshape(height,width)
elif bitDepth == 16:
    dt = np.dtype(np.uint16)
    dt = dt.newbyteorder('>')
    na = np.frombuffer(rawData, offset=offset, dtype=dt).reshape(height,width).astype(np.uint8)
else:
    print(f'ERROR: Unexpected bit depth: {bitDepth}',file=sys.stderr)

# Save either with PIL
Image.fromarray(na).save('result.jpg')
# Or with OpenCV may be faster
cv2.imwrite('result.jpg', na)

---

If you have thousands to do, I would recommend GNU Parallel which you can easily install on your Mac with homebrew using:

brew install parallel

You can then change my program above to accept a filename as parameter in-place of the hard-coded filename and the command to get them all done in parallel is:

parallel --dry-run script.py {} ::: *.IMG

---

For a bit more effort, you can get it done even faster by putting the code above in a function and calling the function for each file specified as a parameter. That way you can avoid starting a new Python interpreter per image and tell GNU Parallel to pass as many files as possible to each invocation of your script like this:

parallel -X --dry-run script.py ::: *.IMG

The structure of the script then looks like this:

def processOne(filename):
    open, read, search, extract, save as per my code above

# Main - process all filenames received as parameters
for filename in sys.argv[1:]:
    processOne(filename)