P: Document the format of RGB LUTs in enhanced profiles

[johnrellis]

If Adobe documents the format of RGB LUTs stored in enhanced profiles, then it will be straightforward for LR plugins to make it much easier for users to import video LUTs as enhanced profiles and apply them to their images. 

There are hundreds, perhaps thousands, of existing LUTs, primarily used for video editing, and most of those are in Rec 709.  There are several roadblocks to users wanting to use those LUTs in LR:

- Camera Raw doesn't allow the Rec 709 gamma 2.2 and 2.4 color spaces when importing a LUT into a new enhanced profile:
https://feedback.photoshop.com/photoshop_family/topics/camera-raw-add-rec-709-to-lut-color-spaces-in...

- A user would need to buy an expensive utility to convert Rec 709 LUTs to a supported color space (e.g. ProPhoto RGB or Rec 2020).

- While LR 7 users will have access to Camera Raw via Photoshop (included in their CC subscription), many of them are unfamiliar with Camera Raw and would find the steps for creating enhanced profiles obscure and daunting.

--------------------------------------
My current surmise for how the LUTs are encoded:

- The LUT is converted to the internal LR/ACR working space (ProPhoto RGB primaries and white point, linear transfer function).

- It is compressed somehow. 

- The compressed LUT is then encoded using a minor variant of Ascii85.

[johnrellis]

I think the SDK does provide all the methods needed for creating the encoded and compressed LUTs in enhanced profiles' .xmp files.

[FeedbackCommunityMember]

As eartho and John Ellis point out, it's in the DNG SDK. Here's a snippet for writing an extended profile:

    dng_xmp *xmp = host.Make_dng_xmp();
   
    dng_string strn;
    
    xmp->Set(XMP_NS_CRS, "PresetType", "Look");
    xmp->SetBoolean(XMP_NS_CRS, "SupportsAmount", true);
    xmp->SetBoolean(XMP_NS_CRS, "SupportsColor", true);
    xmp->SetBoolean(XMP_NS_CRS, "SupportsMonochrome", true);
    xmp->SetBoolean(XMP_NS_CRS, "SupportsHighDynamicRange", true);
    xmp->SetBoolean(XMP_NS_CRS, "SupportsSceneReferred", true);
    xmp->SetBoolean(XMP_NS_CRS, "SupportsOutputReferred", true);
    
    xmp->Set(XMP_NS_CRS, "CameraModelRestriction", "");
    xmp->Set(XMP_NS_CRS, "Copyright", "");
    xmp->Set(XMP_NS_CRS, "ContactInfo", "");
    xmp->Set(XMP_NS_CRS, "Version", "12.3");
    xmp->Set(XMP_NS_CRS, "ProcessVersion", "11.0");
    xmp->SetBoolean(XMP_NS_CRS, "ConvertToGrayscale", false);
    
    strn.Set(name.c_str());
    xmp->SetAltLangDefault(XMP_NS_CRS, "Name", strn);
    strn.Set(group.c_str());
    xmp->SetAltLangDefault(XMP_NS_CRS, "Group", strn);

    dng_look_table look_table;
    look_table.Set(get_dng_hue_sat_map(), 0);
    dng_big_table_storage storage;
    look_table.WriteToXMP(*xmp, XMP_NS_CRS, "LookTable", storage);

    dng_memory_block *blk = xmp->Serialize(false,
                                           0,
                                           4096,
                                           false,
                                           true);

    std::cout << "Writing output XMP profile to " << filename << std::endl;
    std::ofstream outf(filename);
    outf.write(blk->Buffer_char(), blk->LogicalSize());

[FeedbackCommunityMember]

using dng sdk("dng_big_table.cpp" functions) I've replicated with success the alghorithm that decode-decompress / compress-encode the CUBE LUTs into xmp metadata "Table_...", I need a partner to complete this project, write to me: Michele Renzullo.

1) We need to understand how our RGB Values are "transformed" from CUBE(see the output please)

2) We need to recalculate fingerprint(I think it won't be diffuclt)

I've recreated DecodeFromString, DecodeFromBinary, EncodeAsString, EncodeAsBinary funtions. My working code, you need to replace output txt files:

https://gist.github.com/michelerenzullo/a1b8c0a62270dda23c50d483bdcf41d7

CUBE test LUT_SIZE 2X2X2 + XMP encoded CUBE

TITLE "test"
DOMAIN_MIN 0 0 0
DOMAIN_MAX 1 1 1
LUT_3D_SIZE 2
0.274061893 0.219932506 0.177115963  
0.571511126 0.263131176 0.179752179  
0.656680978 0.525461611 0.312991872  
0.852257362 0.575297026 0.347083429  
0.107468354 0.235404972 0.338322431  
0.396458804 0.216070001 0.364647435  
0.273604227 0.545908918 0.545072734  
0.612230119 0.602805907 0.584224470  

#70 #56 #45
#146 #67 #46
#167 #134 #80
#217 #147 #89
#27 #60 #86
#101 #55 #93
#70 #139 #139
#156 #154 #149

#XMP RGB TABLE CONVERTED WITH CAMERA RAW -> 71000OcImwBRLy1{X$/w$i%Whe:T7?%[R'N^`d7etfwl1o9NpBT9x5p.8f[!A?Y$h5751ZDva8xperJFP#'ng/^$B0qItqxe)8

output with my code:

DECODED AND DECOMPRESSED XMP RGB TABLE   -- please see dng_big_table.cpp and dng_big_table.h maybe also dng_fingerprint inside Adobe dng sdk

1 0 0 
0 1 0           <-- some internal flags, seems costant
0 0 3           <-- 3 should be our 3 dimensions
0 0 0 
2 0 0           <-- please note the first number, stands for LUT_3D_SIZE, in our example is "2"
0 
40 70 76 56 86 45              1     <-- problem 1) rgb values aren't sorted! I see a pattern, look the order, seems easy to solve with an alghorithm
130 27 66 60 156 86            5     <-- problem 2) what are the number BEFORE our RGB value? Idk... HSV? HSL? It doesn't seem.
27 168 132 134 31 80           3
10 70 192 139 137 139          7
78 146 91 67 3 46              2
126 101 79 55 89 93            6
45 218 70 147 217 88           4
187 156 81 154 143 149         8
0 0 0     <-- please note the first 0 stands form sRGB
0 1 0     <-- please note the 1 in 2nds position stands for gamma linear
0 0 0
0 0 0 
0 0 0 
0 0 0 
0 0 0 
0 0 0
0 0 0 
64 

[default5atvrwz4xhrv]

Your github gist isn't there anymore. Would you be able to reupload?