go-dng

README

The DNG SDK for linux & go

Adobe's DNG SDK comes with only partial support for building on Linux. The makefiles in this repo will fetch, patch, and compile version 1.6 of the SDK on Linux (tested on Ubuntu 23.04), building the SDK as two static libraries that end up in ./sdk/lib and ./sdk/include.

It also compiles the SDK's dng_validate command, so you can use it on Linux.

Building the SDK on Linux

sudo apt install build-essentials zlib1g-dev libexpat1-dev

git clone https://github.com/abworrall/go-dng.git
cd go-dng

cd ./sdk
make

./bin/dng_validate -v your.dng

Indebted to https://github.com/yanburman/dng_sdk, who did all the work for v1.4

Caveats:

• the makefiles aren't smart
• completely ignores all the CMake stuff in the bundled XML library

Using the SDK from Go

This repo contains a Go wrapper around the lib, that will load and DNG-develop a DNG file, and present it as a standard golang image.Image.

There isn't a way to make go get work automatically with this package, as building the SDK libs require running a makefile. So there are a few steps ...

• step 1: build the SDK, as per the section above.
• step 2: tell the go toolchain where to find the freshly built SDK
• step 3: now you can go get github.com/abworrall/go-dng and it will work

sudo apt install build-essentials zlib1g-dev libexpat1-dev

# Step 1: build the SDK
git clone https://github.com/abworrall/go-dng.git
cd go-dng
cd ./sdk
make
export SDK=`pwd`

# Step 2: tell the go toolchain where the SDK is
export CGO_CPPFLAGS=-I${SDK}/include
export CGO_LDFLAGS=-L${SDK}/lib

# Step 3: use go toolchain to install package, develop, etc
cd ~/my_repos/my_package/
go get github.com/abworrall/go-dng
go run foo/bar

You can install the lib & includes into your system dirs or anywhere else; just make sure the go toolchain can find them.

If you see an error like this when running your go code, or one about missing dng or xmp libraries, then the go toolchain can't find the SDK includes:

$ go test
# github.com/abworrall/go-dng/pkg/dng
dng-wrapper.cpp:3:10: fatal error: dng_color_space.h: No such file or directory
    3 | #include "dng_color_space.h"
      |          ^~~~~~~~~~~~~~~~~~~
compilation terminated.

Caveats for the go wrapper:

• the Go bindings of the API are very incomplete, but easy to extend
• the DNG SDK is in C++, so everything needs to be wrapped into plain old C
• there will be memory leaks, esp in the image handling

Working with rendered data

The DNG development process will render the image into sRGB, doing white balance correction, camera color correction, etc.

import "github.com/abworrall/go-dng/pkg/dng"

func main() {
  img := dng.Image{}
  //img.WhiteBalanceTemp = 5500; // Can override the white reference

  img.Load("my.dng") // `img` is an image.Image

  // See cmd/go-dng-validate/go-dng-validate.go for a longer example
}

Working with Stage 3 data

The SDK provides access to image data at a few points in the development process. Stage 1 is the raw sensor readings, stage 2 is linearized but not-yet-demosaiced.

The stage 3 data is useful; it's been linearized and demosaiced, but color corrections not yet applied - the stage 3 RGB values are in camera-native space. You can also retrieve some color correction values from the DNG, that account for the camera's development profile.

import "github.com/abworrall/go-dng/pkg/dng"

func main() {
  img := dng.Image{ImageKind: dng.ImageStage3}
  img.Load("my.dng")

  // RGB representing a neutral white color, given the white reference point
  asShotNeutral := img.CameraWhite()

  // Matrix mapping camera native colors to 'profile connection space', CIEXYZ
  kindaForwardMatrix := img.CameraToPCS()
}