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[letmaik]

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[mbrown-gh]

Hello! I'm very interested in rawpy, and have a few questions about its suitability for my application, and how to install it (along with LibRaw if necessary) on an RPi.

Briefly, I am designing a color sensor system consisting of an RPi with an RPi camera module (either a V2 or HQ). The functioning of the system is simple: capture an image (with a gray card in the FOV periphery for white balance), and determine the average color of the captured scene (not including the gray card). Ideally all processing will occur on the RPi. The top priority of the system is color accuracy and it's my understanding that I should work with RAW images, and maintain linearity in my processing steps. I have been following this helpful blog post by Jack Hogan on rendering RAW images, which outlines some of the necessary steps: 1) load the RAW image and subtract black levels, 2) white balance, 3) correct linear brightness, 4) clip image data, 5) demosaic, 6) apply color transforms. It seems that at a minimum I could use rawpy to load DNGs output by the RPi libcamera apps into NumPy to then perform these processing steps using basic code I have written myself. However, as outlined in Chapter 5 of the RPi camera algorithm/tuning guide, there are other processing steps that may be necessary to include (e.g. lens shading correction), that are likely too advanced for me to code up myself. A few questions below:

• Could rawpy assist with the above processing steps, either entirely or through a combination of my own processing code and calls to rawpy?
• Can rawpy (and LibRaw) be installed on an RPi (in particular I am hoping to use an RPi Zero W), and could I be directed to instructions for doing so?

Thank you!
Mike

[mbrown-gh]

Thank you! I've recently switched from Matlab to Python, and some of these concepts are a bit foreign - thank you very much for your help!

Re. installing LibRaw, the instructions you linked to for installing from source differ slightly from those provided by LibRaw:

Yours:

git clone https://github.com/LibRaw/LibRaw.git libraw
git clone https://github.com/LibRaw/LibRaw-cmake.git libraw-cmake
cd libraw
git checkout 0.20.0
cp -R ../libraw-cmake/* .
cmake .
sudo make install

LibRaw's:

git clone https://github.com/LibRaw/LibRaw.git
cd LibRaw/
make -f Makefile.dist

The LibRaw folks suggested I follow your instructions (since they are tailored to rawpy), but have subsequently also said they "dropped Cmake support in LibRaw in 2014". When following your instructions, output to the terminal from the cmake command (see below) indicates that some files weren't found. The LibRaw folks indicated that this means I "haven't installed some optional libraries before running cmake", and that I should check with you if rawpy uses those options. Please just let me know how I should proceed. Thanks!

cmake .
-- CMake version: 3.18.4
-- LibRaw string version: 0.20.0
-- LibRaw ID version: 0x0200
-- LibRaw SO version: 20.0.0
-- The CXX compiler identification is GNU 10.2.1
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/c++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Check for LCMS2 availability...
-- Found PkgConfig: /usr/bin/pkg-config (found version "0.29.2")
-- Checking for module 'lcms2'
-- No package 'lcms2' found
-- lcms2 NOT found
-- Check for LCMS availability instead LCMS2...
-- Checking for module 'lcms'
-- No package 'lcms' found
-- Could NOT find LCMS (missing: LCMS_LIBRARIES LCMS_INCLUDE_DIR)
-- Found ZLIB: /usr/lib/arm-linux-gnueabihf/libz.so (found version "1.2.11")
-- Could NOT find JPEG (missing: JPEG_LIBRARY JPEG_INCLUDE_DIR)
-- Could NOT find JPEG (missing: JPEG_LIBRARY JPEG_INCLUDE_DIR)
-- Found OpenMP_CXX: -fopenmp (found version "4.5")
-- Found OpenMP: TRUE (found version "4.5")
-- Could NOT find JPEG (missing: JPEG_LIBRARY JPEG_INCLUDE_DIR)
-- Could NOT find Jasper (missing: JASPER_LIBRARIES JASPER_INCLUDE_DIR JPEG_LIBRARIES)

-- Libraw 0.20.0 configuration
-- Libraw will be compiled with OpenMP support .................. YES
-- Libraw will be compiled with LCMS support .................... NO
-- Libraw will be compiled with example command-line programs ... YES
-- Libraw will be compiled with RedCine codec support ........... NO
-- Libraw will be compiled with DNG deflate codec support ....... YES
-- Libraw will be compiled with DNG lossy codec support ......... NO
-- Libraw will be compiled with RawSpeed support ................ NO
-- Libraw will be compiled with debug message from dcraw ........ NO
-- Libraw will be compiled with Foveon X3F support .............. NO
-- Libraw will be compiled with Raspberry Pi RAW support ........ NO
-- Libraw will be compiled as a shared library

-- Configuring done
-- Generating done
-- Build files have been written to: /home/pi/Desktop/libraw/libraw

[letmaik]

This all looks fine, there's no error, just informational output that some features won't be available either due to missing libraries or because you need to opt-in with flags. There is a flag for some RPi support, so I would probably enable that: instead of cmake . run cmake -DENABLE_6BY9RPI=ON . Then the normal sudo make install.

[mbrown-gh]

Thanks! For anyone following along at some point, using the instructions provided above, I was able to install both libraw and rawpy on a headless RPi, and complete the linked tutorial on inverting a color negative (with custom white balance). I have a few questions on general processing steps with rawpy, but will create a new discussion for that (apologies, I just realized I attached this topic to the welcome discussion). To complete this topic, I have a few final questions below:

• I followed the rawpy instructions for installing libraw. Where is libraw installed in this case? Can I remove the folder I made into which I cloned the libraw repo (the installation output did indicate that build files were written there)? I made that folder on the Desktop - if it can't be removed, is there a better place for it?

• Is there any reason to not follow the libraw instructions for installing libraw from source?

git clone https://github.com/LibRaw/LibRaw.git
cd LibRaw/
make -f Makefile.dist

[letmaik]

libraw is installed in /usr somewhere. You can remove the cloned folders.
You can follow the official libraw installation instructions as well. The reason I'm not using this for my own purposes is that I needed to have something that is consistent across all operating systems that rawpy supports (macOS, Windows, Linux), and CMake does that. The libraw dev doesn't like CMake, which is why it's in a separate community-maintained repo.

[mbrown-gh]

Thanks for the info - I greatly appreciate all your help!