Confusing units in displacement modifier parameters #33781

New Issue

Maxim Vasiliev · 2013-01-06T10:17:19+01:00

Maxim Vasiliev commented

2013-01-06 10:17:19 +01:00

%%%--- Blender version with error, and version that worked ---
2.65.5

- Short description of error ---

When using non-default scene units and/or scale
Option "strength" remains unitless
Option "midlevel" becomes midlevel * base unit.

In fact, according to sources, offset is calculated as:
(texres.tin - midlevel) * strength
The midlevel is applied to texture value, which is normalized to range [0;1] - midlevel expected to be also normalized
The strength is scale that maps range [0;1] to scene units - strength expected to be unit-oriented (and probably named "scale")

- Steps for others to reproduce the error (preferably based on attached .blend file) ---

Create grayscale PNG image with 16bit values from 0 to 65535.
Create image texture, load the image as "non-color" colorspace.
Create grid.
Create displacement modifier with the texture on the grid.
Set midlevel to 0.5 and strength 2.0 (the grid should become with offset -1U to +1U)

Set scene units=metrics, scale=30 (1U = 30m)
Expected results: midlevel remains 0.5, strength becomes 60m (2U)
Observated: midlevel becomes 15m, strength remains 2.0

%%%

%%%--- Blender version with error, and version that worked --- 2.65.5 - Short description of error --- When using non-default scene units and/or scale Option "strength" remains unitless Option "midlevel" becomes midlevel * base unit. In fact, according to sources, offset is calculated as: (texres.tin - midlevel) * strength The midlevel is applied to texture value, which is normalized to range [0;1] - midlevel expected to be also normalized The strength is scale that maps range [0;1] to scene units - strength expected to be unit-oriented (and probably named "scale") - Steps for others to reproduce the error (preferably based on attached .blend file) --- Create grayscale PNG image with 16bit values from 0 to 65535. Create image texture, load the image as "non-color" colorspace. Create grid. Create displacement modifier with the texture on the grid. Set midlevel to 0.5 and strength 2.0 (the grid should become with offset -1U to +1U) Set scene units=metrics, scale=30 (1U = 30m) Expected results: midlevel remains 0.5, strength becomes 60m (2U) Observated: midlevel becomes 15m, strength remains 2.0 %%%

Maxim Vasiliev commented

2013-01-06 10:17:19 +01:00

Changed status to: 'Open'

Campbell Barton commented

2013-01-14 21:28:48 +01:00

%%%Checked the displace modifier, it was incorrectly using units for mid-level (fixed in svn r53799).

But there is certainly some odd stuff going on with PNG saving/reloading using different colors.
Assigning to Sergey.%%%

%%%Checked the displace modifier, it was incorrectly using units for mid-level (fixed in svn r53799). But there is certainly some odd stuff going on with PNG saving/reloading using different colors. Assigning to Sergey.%%%

Campbell Barton commented

2013-01-14 21:50:39 +01:00

%%%Checking further, this may be an issue in the displace modifier, taking back the bug :)%%%

Campbell Barton commented

2013-01-15 08:49:56 +01:00

%%%Found the problem.

Selecting a new image with 0.5 and a float buffer creates the image buffer in linear color space. (ok)
Saving the float buffer as a 16bit PNG writes the floats as 16bit unsigned shorts with no rec709->sRGB conversion.
Loading the 16bit PNG loads the image as sRGB.

Attached a patch that applies the same logic used when saving Jpeg200 from float buffer.%%%

%%%Found the problem. - Selecting a new image with 0.5 and a float buffer creates the image buffer in linear color space. (ok) - Saving the float buffer as a 16bit PNG writes the floats as 16bit unsigned shorts with no rec709->sRGB conversion. - Loading the 16bit PNG loads the image as sRGB. Attached a patch that applies the same logic used when saving Jpeg200 from float buffer.%%%

Campbell Barton commented

2013-01-15 09:10:44 +01:00

%%%fixed r53807.%%%

Campbell Barton commented

2013-01-15 09:10:45 +01:00

Changed status from 'Open' to: 'Resolved'

Campbell Barton closed this issue

2013-01-15 09:10:45 +01:00

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Confusing units in displacement modifier parameters #33781