Sharing rating between Digikam and Rawtherapee

There are several XMP tags that DigiKam writes for ratings, but the most important one will be:

xmp:Rating="0"   // values 0 (none) to 5
digiKam:ColorLabel="0"  // values 0 (none) to 9.
// xmp:Label is used only if it is a Lightroom-compatible color

RawTherapee uses:

[General]
Rank=0         // values 0 (none) to 5
ColorLabel=0   // RawTherapee uses only 5 colors (0-5)

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If you feel brave enough, you can use regex to transfer the information from PP3 to XMP or vice versa.

Steps:

1. Download images from camera (d'uh).
2. Open them on Digikam. Delete bad shots, rate the rest of the shots (make sure that XMPs are written).
3. Open RawTherapee and open the files' folder. This should write the .pp3 files for all images. Close RT / go to a different folder.
4. Regex it - We will dive into that in a moment!
5. Open the folder again with RT. Enjoy how easily text files are manipulated.

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I created a Python (version 3) script that does the regex-operation for all PP3s and XMPs in a folder.

NB: This code might damage your sidecar files. It might not work with other versions than DigiKam's 6.3.0 and RawTherapee's 5.7. Make a backup first, then try this!

Walkthrough for above-mentioned 4.:

• Make sure DigiKam has set a color tag: if you do not have any set, apply one, save metadata, delete the color, save metadata again.
• Install Python,
• Open a console, cd to the folder with the images,
• python <path to your python script>, where your script is:

import re
from pathlib import Path

# Find only *.pp3 and *.xmp in this folder, keep only those that have a twin with the other extension:
found_pp3 = [str(x.resolve()) for x in Path("./").glob('*.pp3') if
             Path(re.sub('.pp3$', '.xmp', str(x.resolve()), flags=re.MULTILINE)).is_file()]
found_xmp = [str(x.resolve()) for x in Path("./").glob('*.xmp') if
             Path(re.sub('.xmp$', '.pp3', str(x.resolve()), flags=re.MULTILINE)).is_file()]       
print(str(len(found_pp3)) + " | " + str(len(found_xmp)) + " files found.")

# Making sure that A.pp3 is used as the same time as A.xmp:
found_pp3 = sorted(found_pp3, key=str.lower)
found_xmp = sorted(found_xmp, key=str.lower)

# Having fun with regex:
i = 0
while i < len(found_pp3):
    print(found_xmp[i] + " --> " + found_pp3[i])
    # Copying content of 1st/2nd/... file into variable:
    temp_xmp = Path(found_xmp[i]).read_text(encoding='utf-8')
    temp_pp3 = Path(found_pp3[i]).read_text(encoding='utf-8')
    # Substituting Stars (aka rank/rating) from xmp to pp3:
    temp_xmp_rating = re.search('xmp:Rating="(.+?)"', temp_xmp).group(1)
    temp_pp3 = re.sub('Rank=d', 'Rank=' + temp_xmp_rating, temp_pp3)
    # Substituting color-tags from xmp to pp3:
    temp_xmp_color = re.search('digiKam:ColorLabel="(.+?)"', temp_xmp).group(1)
    # DigiKam has 0-9 tags, RawTherapee 0-5.
    # Translate orange to yellow and grey/white/black to none:
    if(int(temp_xmp_color) == 3):
        temp_xmp_color = "4"
    elif(3 < int(temp_xmp_color) <= 6):
         temp_xmp_color = str(int(temp_xmp_color) - 1)
    elif(int(temp_xmp_color) > 6):
        temp_xmp_color = "0"
    temp_pp3 = re.sub('ColorLabel=d', 'ColorLabel=' + temp_xmp_color, temp_pp3)
    # Overwriting the pp3:
    Path(found_pp3[i]).write_text(temp_pp3, encoding='utf-8')
    i += 1

print("Done!")

I made a repository for this code which now can also work in the opposite direction. It works well for me so far, but again:

NB: This code might damage your sidecar files. It might not work with other versions than DigiKam's 6.3.0 and RawTherapee's 5.7. Make a backup first, then try this!

It should do well, though, especially as long as RawTherapee keeps using Rank= and ColorLabel= without ambiguity (if they rename them, the script will not change anything) and DigiKam does the same with xmp:Rating= and digiKam:ColorLabel=.