[Cin] oops apparently 'subtract' mode is broken!

[Phyllis Smith]

And now here is the forgotten attached!

On Sat, Oct 1, 2022 at 7:27 PM Phyllis Smith <phylsmith2017 at gmail.com>
wrote:

>
> more documentation, it seems Adobe products use shared code for this ....
>>
>>
>> https://www.rippletraining.com/blog/final-cut-pro-x/understanding-blend-modes-final-cut-pro/
>>
> Using the above URL for comparison, I used it on current CinGG and HV
> 4.6.1 for subtract.  HV matches and GG does not.  So tomorrow I will look
> at the code that Andrew quoted below to see if adding the specific guard
> corrects the issue.  In the attached, top left is HV 4.6.1 and bottom left
> is GG current with right side the URL.
>
>>
>>
>> --quote---
>>
>> Subtract
>>
>> Subtract does what it advertises; the color values of one layer are
>> subtracted from the other layer. This tends to have a net darkening effect.
>> Pixel values can’t fall below zero, so negative numbers are rendered to
>> black.
>>
>>
>> ---end quote---
>>
>>
>> in older cingg code (from 4.6.mod era - earliest public code on Google
>> code) I see such construct :
>>
>>
>> /data/data/com.termux/files/home/cingg-g~nelerra-4.6.mod/cinelerra/overlayframe.C
>>      4762/69317  UTF-8        6%
>>
>>                         break; \
>>
>>                 case TRANSFER_SUBTRACT: \
>>
>>                         r = (temp_type)output[0] - (temp_type)input1; \
>>
>>                         g = ((temp_type)output[1] -
>> (temp_type)chroma_offset) - \
>>
>>                                 ((temp_type)input2 -
>> (temp_type)chroma_offset) + \
>>
>>                                 (temp_type)chroma_offset; \
>>
>>                         b = ((temp_type)output[2] -
>> (temp_type)chroma_offset) - \
>>
>>                                 ((temp_type)input3 -
>> (temp_type)chroma_offset) + \
>>
>>                                 (temp_type)chroma_offset; \
>>
>>                         if(r < 0) r = 0; \
>>
>>                         if(g < 0) g = 0; \
>>
>>                         if(b < 0) b = 0; \
>>
>>                         r = (r * opacity + output[0] * transparency) /
>> max; \
>>
>>                         g = (g * opacity + output[1] * transparency) /
>> max; \
>>
>>                         b = (b * opacity + output[2] * transparency) /
>> max; \                                                              break; \
>>
>>
>> ---
>>
>>
>> so it basically had specific guard against going negative. Not sure if
>> our implementation does the same just in different place?
>>
>>
>> I see no specific handling of it in macros ...
>>
>>
>>
>> overlayframe.h     [----] 38 L:[ 53+ 0  53/615] *(1572/17155b) 001[*][X]
>>
>> // ADDITION<--->[(Sa + Da), (Sc + Dc)]
>>
>> #define ALPHA_ADDITION(mx, Sa, Da) (Sa + Da)
>>
>> #define COLOR_ADDITION(mx, Sc, Sa, Dc, Da) (Sc + Dc)
>>
>> #define CHROMA_ADDITION COLOR_ADDITION
>>
>>
>> // SUBTRACT<--->[(Sa - Da), (Sc - Dc)]
>>
>> #define ALPHA_SUBTRACT(mx, Sa, Da) (Sa - Da)
>>
>> #define COLOR_SUBTRACT(mx, Sc, Sa, Dc, Da) (Sc - Dc)
>>
>> #define CHROMA_SUBTRACT COLOR_SUBTRACT
>>
>>
>> but apparently you can add some comparing here ...just .. it went from
>> two-stage process to single stage for untrained eye and I am not sure where
>> to put those ifs?
>>
>>
>>
>>
>>
>>
>>>
>>> вс, 25 сент. 2022 г., 11:06 Andrew Randrianasulu <
>>> randrianasulu at gmail.com>:
>>>
>>>> I found Graphics-softlight mode behaving visually close...but not sure
>>>> how close to CinHV/CV subtract mode ...
>>>>
>>>>
>>>>
>>>> вс, 25 сент. 2022 г., 10:24 Andrew Randrianasulu <
>>>> randrianasulu at gmail.com>:
>>>>
>>>>> I was trying to repeat tuto at
>>>>>
>>>>> https://linuxvideoediting.blogspot.com/2022/01/transparent-text-effect-in-Cinelerra-part1.html?m=1
>>>>>
>>>>>
>>>>> so I loaded video, created empty new vid track, applied 'titles',
>>>>> 'blur' and 'invert video' to _empty track_, then set track's mode to
>>>>> subtract .... result was color inversion of original video on second vid
>>>>> track (
>>>>>
>>>>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.cinelerra-gg.org/pipermail/cin/attachments/20221002/cd61eb08/attachment-0001.htm>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: HVvsGG.gif
Type: image/gif
Size: 134228 bytes
Desc: not available
URL: <https://lists.cinelerra-gg.org/pipermail/cin/attachments/20221002/cd61eb08/attachment-0001.gif>