DPX sequences from CineForm cf2dpx import to Assimilate SCRATCH

[danibam]

LIN or LOG are just flags in the DPX file header. In SCRATCH, as in many other applications, this flag in the DPX file header is used
by the software to display it properly. In combination with the AUTOAPPLY option in the Preview LUT (Player Settings) you get
the behavior you are describing: A file flagged as LOG is being loaded and a Log2Lin Preview conversion is being AUTOAPPLIED
to it for previewing. The result is you "see" (preview) the file through a Log2Lin conversion ... which you can set to a specific
custom Lab Preview LUT emulating their filmout process if you want.

As Barend explains, if you set the flag to LIN then AUTOAPPLY will interpret that the file in not LOG and will not apply any preview conversion.

You may as well change the Preview LUT settings (player settngs) and turn off all preview LUTs/conversions.

When you preview the file in RESOLVE no LUT is applied to it because you have not set up such preview parameter in settings.

Nothing wrong with SCRATCH here ... simply interpreting file header metadata using one of SCRATCH preview settings:
AUTOAPPLY by default. SCRATCH will default to whatever setting was used during its last session.


Daniel Perez

 

[danibam]

Can one assume that Scratch uses HD limits of 64-940 by default for so called "LIN" monitor gamma DPX, or does it load 0 to 1023, and map that to 0-255 for 8 bit graphic cards by linear scaling? Or does it map 0-1023 to 16-235? Or map 64-940 to 0-255?

For the "LOG" files, does Scratch automatically apply softclip to push the highlights from 1023 down to 685, or does it automatically clip all file data above 685 off for default conversion of LOG to monitor gamma?

SCRATCH will not alter your file. If it is full range it will continue in full range ... if it is not it will remain the same when you load it. From there on you will always be using the full range while grading. Nothing is being converted here .... just being previewed through a Preview LUT so you can see the file properly. All grades happen to the original range. The preview transform has soft clip options. Look in Settings/LUT inside the Player.

Does Scratch default 8 bit monitor gamma in the range of 0-255 or 16-235?

Look in System Settings where the SDI output is configured. You can set SCRATCH to work in either full range or legal range for previewing. Nevertheless all grading still occurs in full range. Turn on the Statistics (Histogram and Scopes) to better see the used range.


Daniel Perez

 

[Dan Hudgins]

LIN or LOG are just flags in the DPX file header. In SCRATCH, as in many other applications, this flag in the DPX file header is used
by the software to display it properly.
Daniel Perez

I looked at the header and it says:

DPX image information header . image element[1] . transfer = 0
DPX image information header . image element[1] . colormetric = 0

Those both are "user defined" so there is no LOG = 3 or LIN = 2 value set by cf2dpx, maybe some should talk to Cineform (tm) about why that is?

I looked at the data and it ranges from code values about 5 to 983, so I guess its a "full range" user-defined transfer curve.

In the case of "user defined" then SCRATCH should default to LIN = full range no curve, rather than default to LOG 95-685 since the curve is unknown, or at least not setup by the DPX file?

 

[Dan Hudgins]

Does compatibility exist between DPX from cf2dpx and SCRATCH,

If you set SCRATCH to force LIN and monitor to full range, then I don't think the major part of your image problems are with SCRATCH.

It seems you have one or more of these problems:

1) You overexposed your shot by two to three stops.

2) You are using the wrong transfer curve for Cineform (tm) to DPX conversion.

3) The Cineform (tm) data was made using the wrong transfer curve for sensor linear to EI/ISO and white balance since the highlights are blasted and the black seem out of balance. In otherwords if you had the sky at about 0.6 normalized sensor signal for the green pixels, the EI/ISO and white balance should not show the highlights blased if the Cineform (tm) was to record the sensor data using 12bit Bayer format. If you overexposed the sensor, then your Cineform (tm) is also overexposed, and you can only re-shoot with the right exposure level and more fill lights. Cineform (tm) Bayer should be able to capture 12bits sensor data without loss of the upper bits (although there may be some scaling errors if it used an encode-decode curve to save space). Cineform YUV requires that the camera "pre-correct" the data before it is recorded, so any use of the wrong curve in the camera ends up as burned into your data, what goes off the top is lost before it gets to Cineform (tm).

4) You are using a camera that is not calibrated right and overexposing because the viewfinder is not working right.

 

[danibam]

I looked at the header and it says:

DPX image information header . image element[1] . transfer = 0
DPX image information header . image element[1] . colormetric = 0

Those both are "user defined" so there is no LOG = 3 or LIN = 2 value set by cf2dpx, maybe some should talk to Cineform (tm) about why that is?

You may want to send one of these DPX files to support@assimilateinc.com with the explanation above so they can have a look at it. All I can say as a user is that SCRATCH is interpreting the header metadata in the DPX files as LOG ... and behaving accordingly.

I looked at the data and it ranges from code values about 5 to 983, so I guess its a "full range" user-defined transfer curve.

In the case of "user defined" then SCRATCH should default to LIN = full range no curve, rather than default to LOG 95-685 since the curve is unknown, or at least not setup by the DPX file?

SCRATCH is clearly interpreting the file as LOG ... not sure if by mistake. Great thing inside SCRATCH is that each file individually, or groups of clips in batches using the Media Browser, can easily have their metadata flag reset to LIN without altering the original files.

About LOG 95-685 ... SCRATCH does not really care about the range. If flagged LOG and the AUTOAPPLY setting is ON in the Preview Settings (both conditions required) then it previews the footage through a custom film lab Preview LUT. Such LUTs are usually by default 95-685, but they don't have to be. When no specific custom LUT is defined, SCRATCH defaults to an algorithmic Log2Lin preview conversion, set by default to 95-685, SoftClip 16 and Gamma 1.0 ... meaning with Gamma 1.0 that whatever the current display gamma is it remains the same (unaltered).

Note that 95-685 are 10 bit values ... widely used in our industry due to the common use of DPX 10bit Log files. Nevertheless SCRATCH's color engine is a floating point engine, working in either half-foat or full-float depending on user settings. All LUTs, gamma adjustments ... and in general all color transformations are performed in floating point. No need to worry about the bit depth of the LUT being used. When loaded in SCRATCH all LUTs (or any other color transformation matrix) are interpreted and converted accordingly. When applied to the image it all happens in floating point.

Daniel Perez

 

[Gerry Lee]

Pihlaja View is a DPX image sequence viewer
http://pihlaja.org/?sdmon=files/trial/PihlajaView-0.9.1beta-trial.dmg

DPX(DPX from cf2dpx) file header info view in Pihlaja

 

[Dan Hudgins]

As I pointed out there is no LIN or LOG in the sample DPX from cf2dpx, I assume that may be due to the camera meta-data not being used to set the transfer curve so the "user defined" is set.

I do have a question, there is a transfer = 1 option in DPX files for "Printing density", what does SCRATCH do in that case, does it set LOG or LIN?

The DPX spec says these values are valid for the transfer field (table 5a),

0 User defined
1 Printing density
2 Linear
3 Logarithmic
4 Unspecified video
5 SMPTE 240M
6 CCIR 709-1
7 CCIR 601-2 system B or G (625)
8 CCIR 601-2 system M (525)
9 Composite video (NTSC); see SMPTE 170M
10 Composite video (PAL); see CCIR 624-4
11 Z (depth) -- linear
12 Z (depth) -- homogeneous (distance to screen and angle
of view must also be specified in user-defined section)
13-254 Reserved for future use


And for the colormetric field (table 5b),

0 User defined
1 Printing density
2 Not applicable
3 Not applicable
4 Unspecified video
5 SMPTE 240M
6 CCIR 709-1
7 CCIR 601-2 system B or G (625)
8 CCIR 601-2 system M (525)
9 Composite video (NTSC); see SMPTE 170M
10 Composite video (PAL); see CCIR 624-4
11 Not applicable
12 Not applicable
13-254 Reserved for future use
1)The codes are assigned to correspond to those in table 5A, except where
there is no appropriate colorimetric specification.

Note that colormetric says in both 3=log and 2=lin that it is "not applicable" in that case, what colormetric code(s) does SCRATCH expect for colormetric?