Contrast filter, meaning of params and a suggestion

[guju]

I found nowhere description about the settings
"MPEG2->PC", Luma, ChromaU and ChromaV.

I suspect "MPEG2->PC" has to to something with the borders
of luma or so? (DVD is restricted to ... and has to changed
to ... when watching on PC?). Please explain, and if only
in a tool tip.

Also the checkboxes Luma, ChromaU and ChromaV:
Does it mean that only the activated component is effected
when changing contrast/ brightness?
However I don't see any difference when checking/ dechecking
ChromaU or -V...

Also I would suggest to add a reset button for the settings.

[guju]

Knowbody to explain?

I have never seen the option for U and V @ brightness/contrast filter.

And the "MPEG2->PC" thing? (I suspect something about range transformation...?)

[eumagga0x2a]

Please explain, and if only in a tool tip.

I agree that the current button label is somewhat confusing as the subject is not specific to MPEG2.

I suspect something about range transformation...?

Exactly, it sets the parameters and the controls to perform color range conversion from limited / MPEG color range (16 - 235) to the full one (0 - 255), please see https://en.wikipedia.org/wiki/YCbCr.

Also the checkboxes Luma, ChromaU and ChromaV:
Does it mean that only the activated component is effected when changing contrast/ brightness?
However I don't see any difference when checking/ dechecking ChromaU or -V...

U and V checkboxes affect the picture only when changing contrast. Deselect Luma, and you can adjust color saturation by modifying contrast.

[guju]

Thank you for your help.

Still the simple function of changing brightness and contrast
is somewhat confusing in Avidemux.
Actually I have never seen the checkboxes for L, U and V in
this context, also the range transformation button.
Probably I'm not the only one who is confused about it.

Questions that arose:
What kind of movies need the range transformation?
Maybe some of them are automatically transformed by player?
How do I recognize the movies that need transformation?
The wikepedia article surely is much too complex and no
help for a typical user.

The checkboxes for L, U and V:
How does this correspond to the normal, simple brightness/ contrast
filters you see everywhere else?
By default Avidemux has L, U and V enabled, but this doesn't
seem the typical brightness/ contrast filter
(is it just L there?).

Suggestions moreover:

A reset button for the settings.
Peek original button should effect shown histogram.
Histogram shows only L? It should be labelled so.

To my experience the whole area of AV consists of
exceptions of exceptions of exceptions...
Complex to the infinite.
In this situation it might be good to have all options.
BUT they should be well explained, especially when they
are non-standard.
Just giving the complexity to the users will lead
for certain to misuse and worsening the quality of AV.

Please take this as constructive feedback please

[guju]

Addendum to limited color range:

If in Avidemux I open a movie (origin: DVD) where "Information" says "Color Range: Limited (MPEG)",
and Save a frame as Image, then the luma has full range 0..255...

[eumagga0x2a]

What kind of movies need the range transformation?

Probably when appending / mixing videos with different color range.

Maybe some of them are automatically transformed by player?

Yes, most video outputs invoked by video players automatically bump contrast, many video players evaluate VUI (video usability information) from codec extradata and / or stored in the container which can hint that the video doesn't need this contrast enhancement.

How do I recognize the movies that need transformation?

If you have configured encoder to accept full range input and the histogramm shows that input always fits inside the limited range, you might want to use this preset (the button just sets the controls accordingly). Usually you don't need to touch it.

The checkboxes for L, U and V:
How does this correspond to the normal, simple brightness/ contrast filters you see everywhere else?

I don't see brightness / contrast filters everywhere ;-)

By default Avidemux has L, U and V enabled, but this doesn't seem the typical brightness/ contrast filter
(is it just L there?).

This filter operates on the three planes (Y = luminance, V = "red" chrominance component, U = "blue" chrominance component). Unchecking a checkbox allows to exclude the corresponding plane from being modified. As already stated, the brightness dial operates only on luminance, the contrast one on all planes (if checked).

A reset button for the settings.

You might want to have a look at the "MPlayer eq2" filter (all sliders can be reset via context menu).

Peek original button should effect shown histogram.

I understand your reasoning, though this would probably require modifications to all filters as histogram is redrawn only when the processed picture is updated (the histogram code is contained within the function which processes the input for preview) while the button simply swaps the processed picture with the unprocessed source in the base (in the parent) class.

Histogram shows only L? It should be labelled so.

A honest question: would a chroma component histogram be of any use? If a histogram refers to RGB, then yes, of course, it must be made clear which color the histogram describes (usually by using the respective color to draw it). But if we operate on input, already separated in luma and chroma??

If in Avidemux I open a movie (origin: DVD) where "Information" says "Color Range: Limited (MPEG)",
and Save a frame as Image, then the luma has full range 0..255...

Yes, that much of comfort should be, the automatic expansion of color range was added because users IMHO justly complained that seeing a normally saturated picture in Avidemux preview and getting a watered down, pale JPEG export is poor UX. JPEG presumes the full color range.

[guju]

Thank you for your answers!

Now I understand WHY you did it that way.
Still, I don't agree in many of it.

If you make some step backwards and have a look on the issues
with the eyes of a "typical" user
(I mean someone whose daily home is not the AV jungle
with all its details, expeptions and pitfalls)
than you maybe understand what I'm about.

It reminds me a little bit at that extreme
video program named "SUPER", where you could
produce the most strangest constellations,
in a most strange "GUI".

(To prevent making the post hyper-complex
I don't use citation again)

The "typical" brightness/ contrast filter:
What I mean:
If there are filters in a video app at all,
b/c will be there.
And there will be no options to choose channels.
I suspect this typical behaviour of "all other" apps
is when you deselect U and V?
But selected all is the default in Avidemux.
No good.

Hint to the filter "MPlayer eq"
Yes, but we're about the normal b/c filter here,
aren't we?

Peek orginal button should effect histogram.
Implementation details should never reason bad GUI.

Histogram labelled with "L"
I was not talking about extending the histogram
to show also U and V, just labelling it with "L".

Please, I don't want to be right or so.
I just want to give you my personal feedback
to improve Avidemux.

Actually what's missing most is a minimal kind
of docu/ help in Avidemux.
Maybe just a small explanation behind "F1"?
Then maybe many questions wouldn't arise at all.
(Like mine for example )

[eumagga0x2a]

Now I understand WHY you did it that way.

There is a big misunderstanding: while I added a few features, fixed some bugs and made UX here and there more user-friendly from my POV (and szlldm added a whole lot of new filters, artwork and UX enhancing features), almost all here had been created many years earlier by the author of Avidemux. I have no intention and capacity to mount the work needed to redesign the application.

I suspect this typical behaviour of "all other" apps is when you deselect U and V?

No, definitely not. The default configuration of the "contrast" filter in Avidemux matches the expected operation of such a filter. The option to deselect components might have been added just because the implementation made this step easy.

Hint to the filter "MPlayer eq"
Yes, but we're about the normal b/c filter here, aren't we?

eq2 is a normal brightness / contrast filter with some substantial extra features added.

Peek orginal button should effect histogram.
Implementation details should never reason bad GUI.

This might introduce a perceptible delay when switching to unprocessed picture, but I agree with your reasoning. Probably not enough of a bug for me to put any effort into a fix right now 

Please, I don't want to be right or so. I just want to give you my personal feedback to improve Avidemux.

Absolutely no issue with that, your suggestions are welcome.

Actually what's missing most is a minimal kind of docu/ help in Avidemux.

I don't think that bundled (offline) help might be very beneficial, but the pitiful state of abandoned Avidemux Wiki is my fault. I don't feel knowledged enough to update it at the level it was written initially, back in the days of Avidemux 2.5.x, and the inflow of tasks results in documentation falling off the cliff.

[guju]

Again: Thank you for your explanation.

I didn't knew the context of Avdemux' dev.

Thank you for improving, expanding and maintaining it.