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IDProjectCategoryView StatusLast Update
0000272Cinelerra-GG[All Projects] Featurepublic2019-07-18 14:06
ReporterMatNAssigned To 
Status newResolutionopen 
PlatformX86_64OSMintOS Version19.1
Product Version2019-06 
Target VersionFixed in Version 
Summary0000272: Video effect "brightness/contrast", add option to to change contrast yet keep the bottom (black) the same.
DescriptionCurrently, is you want to adjust brightness, the whole video signal shifts upwards, which is what you want.
But if you adjust contrast, the signal changes with respect to some middle point about halfway (as seen in videoscope-waveform). That means that for every brightness adjustment, you have to adjust contrast as well.
If the contrast "null point¨ could be placed at the 0 level also, that would save time when adjusting varying brightness levels.
Implemented as a clickable option, or (more flexible but is it useful) a value 0-100 that defines the contrast adjustment baseline. E.g. currently it is about 50, 0 would keep the black level unchanged, 100 would keep the high level unchange, or anything in between.
Steps To ReproduceLoad a video, put the brightness/contrast effect on it, then the videoscope. Open both. In the videoscope, select only "waveform¨.
Play the video a little, stop it. Change contrast. The videoscope shows it varying both above and below the 50 line.
TagsNo tags attached.




2019-07-18 14:06

reporter   ~0001942

Hi IgorBeg,
If I look at the videoscope, the two do not seem to be connected. Brightness shifts the whole waveform up or down, contrast changes the total size of the waveform. I have not recently tested it, but I think my TV acts the same. Brightness changes the black level, contrast does not. Contrast on the TV makes only the highs more or less brighter.


2019-07-18 11:33

reporter   ~0001940

Hi MatN,
Brightness and Contrast are connected together. It is not possible to detach one each other.
If you have a probe to calibrate your monitor you know what I say: when you change contrast parameter also brightness changes its value.
To take another example with something you know (I think), in photography you have Aperture, Exposition Time, and ISO (sensibility). In the same condition,when You have take a shot if you want to increase of a “stop”, you can change Aperture, and the photocamera will change the Exposition Time value, or change Exposition Time, and the photocamera will change the Aperture value. Of course, if you change ISO value, the others two parameters, Aperture and Time, change. The light that enter in the camera’s sensor (film, in analog camera) is the same but the two parameters are different.

In your case I would use Histogram Bezier plugin, more powerful than Brightness/contrast plugin. Usually Brightness/Contrast plugin is used for minor adjustment.

I think so.

Issue History

Date Modified Username Field Change
2019-07-18 09:31 MatN New Issue
2019-07-18 11:33 IgorBeg Note Added: 0001940
2019-07-18 14:06 MatN Note Added: 0001942