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| John I. |
| Posted: Jul 19 2010, 05:27 PM |
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There are two points, and the first has intrigued me for quite some time, and I'm not sure if these are bugs or by design.
(Using Virtualdub up to 1.9.10 (X) build 33815)
The first, is the contrast filters in Virtualdub (whether internal or external.)
When applying a contrast filter to a frame (increase), the bright end is increased, while keeping the dark end in place.
On the other hand, applying contrast in TMPGEnc, Adobe Premier, Photoshop, Paintshop etc..., the bright end is increased and the dark end is decreased.
(1) Original frame histogram:
|______iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii_____|
(2) Contrast in Virtualdub:
|______iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii_|
(3) Contrast in other Video and Image applications:
|_iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii_|
If one needs to achieve this in Virtualdub, two sliders will have to be used. The brightness decreased, and contrast increased.
Now, also in reverse , when decreasing contrast, and all the way approaching the 0%, the image becomes darker until totally black.
(1) Original frame histogram:
|_iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii_|
(2) Contrast in Virtualdub:
|_iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii__________________|
(3) Contrast in other Video and Image applications:
|______iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii______|
Again, both the two sliders will have to be applied to reach the desired effect.
_______________
The second, is the curve editor display.
If a blend is applied to any filter, and the curve editor display is enabled, going into filters for further adjustments to any filter, causes the curve editor display to alternate between normally showing the curve and no curve displayed with only the gray background of Virtualdub showing. This also happens without modifying any filter. (Try CTR+F then ESC.)
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| Jam One |
| Posted: Jul 19 2010, 06:25 PM |
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It's good to hear that. That means brightness and contrast work in the best way they could have.
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| John I. |
| Posted: Jul 19 2010, 07:24 PM |
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Does that mean that the least contrast should be black ? |
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| phaeron |
| Posted: Jul 20 2010, 05:11 AM |
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The reason for the brightness/contrast filter working this way is historical -- it's just the way that I implemented it, not having seen how other programs work.
As for the curve editor, I can't seem to reproduce this. Any specific filter count or order of operations needed to trigger it?
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| Jam One |
| Posted: Jul 20 2010, 05:50 AM |
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Regarding the VIDEO,
"contrast" controls the transfer function, i.e. the White Level
"brightness" controls the Black Level.
That's the way it should be.
"The least contrast" should ideally (but not necessarily, in real world) be "the level of brightness". |
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| John I. |
| Posted: Jul 20 2010, 06:28 AM |
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phaeron, I am aware of what you mean, as I've been using virtualdub since V 1.3, and this is why I presented it as 'not sure if it is a bug or by design'.
As I didn't want to impose my understanding of 'Contrast', I did a search on the net to double check my knowledge, and I found some intersting links such as the following:
http://en.wikipedia.org/wiki/Contrast_%28vision%29
Is it possible to offer both sliders behaviors as choices in the 'Brightness & Contrast' Dialog ?
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For the curve Editor:
if the blended filter is not the first in order in the Filter list, the curve editor starts exhibiting this behavior.
The simplest setup that triggers this is:
- Open any AVI.
- Add 'Brightness & Contrast' Filter only (No need to adjust settings.)
The Curve display is stable.
- Add 'NULL Transform' as 2nd filter (No need to adjust settings.)
The Curve display is stable.
- Move the 'NULL Transform' up to be first in order.
Now, if you go in and out of the filters list, the curve editor keeps disappearing and reappearing.
- Move the blended 'Brightness & Contrast' to first position, and the curve editor becomes stable again.
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| Jam One |
| Posted: Jul 20 2010, 11:08 AM |
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1)
| QUOTE (Wikipedia.org) | | This article needs attention from an expert on the subject. |
Yes, it does.
2)
You may wish to read more about Displays, particularly about displays adjustment and calibration.
What you refer to is sometimes called "linear contrast", where the luminosity "rotates" around the middle-gray (middle power) level/point.
This method is a tradition for Photo-editing.
But Video is a different realm. One of the points in its difference is Video is destined for Displays solely. And displays normally sport the abovementioned behavior.
'Contrast' is just a familiar name given to the power-of-transfer-function control.
'Brightness' is just a familiar name given to the "zero level" of the transfer function.
Note that the 'black level' is a term which requires some understanding of its relation to the certain medium. What is black on TV display is not supposed to be black on PC display (it is supposed to be dark-gray on PC). |
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| v0lt |
| Posted: Jul 20 2010, 01:23 PM |
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To heap. Old cosmetic bug:
I already wrote about this, but there was no answer. |
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| John I. |
| Posted: Jul 20 2010, 08:41 PM |
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Jam One,
I'm not opposed to your technical description and justification that the
| QUOTE | | brightness and contrast work in the best way they could have |
particularly, when this method is meant to prevent the generation of non-existing artifacts in the output.
But, even when set this way, the filter has side effects:
| QUOTE | | saturation is affected by contrast, and hues can shift if clamping at white or black occurs' (Virtualdub help) |
Perhaps I didn't clarify in the first place that I was aiming at the general users who could have a washed out video or capture at their hand and are only aware of the common use of a contrast control, hence, my proposal to
| QUOTE | | offer both sliders behaviors as choices in the 'Brightness & Contrast' Dialog. |
Mentioning the Virtualdub help leads me to another suggestion.
Phaeron, in the help file, you recommend the use of 'Levels' over "Brightnes/Contrast. Is it possible to add a Histogram display of after the controls are applied in both filters ? This will ensure that users work within the safe limits, specially, when only having the preview window as a reference could be misleading in cases such as aging monitors, and badly or misconfigured displays.
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| Jam One |
| Posted: Jul 20 2010, 09:55 PM |
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John I.,
I'd like to assure you I, in turn, am not opposed to the point of yours!
I was kind of explaining some ideas "alternative" to photographic customs.
'Levels' filter is capable of matching your exact need - adjusting that very sort of contrast you wish.
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| phaeron |
| Posted: Jul 21 2010, 05:56 AM |
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Fixes queued for the curve editor and menu item description bugs.
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| Loadus |
| Posted: Jul 22 2010, 10:25 PM |
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| QUOTE (John I. @ Jul 20 2010, 02:41 PM) | | Is it possible to add a Histogram display of after the controls are applied in both filters ? This will ensure that users work within the safe limits, specially, when only having the preview window as a reference could be misleading in cases such as aging monitors, and badly or misconfigured displays. |
Well, you shouldn't use Brightness/Contrast // Levels at all for correction work. At least not on a (linear or) gamma workspace (meaning the normal editing space VirtualDub and sRGB use).
--------------------
deviantART behance |
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| John I. |
| Posted: Jul 22 2010, 11:48 PM |
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Loadus,
If I shouldn't, then, you are pointing me to ... ?
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| John I. |
| Posted: Jul 24 2010, 10:03 PM |
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phaeron,
There is another issue with curve editor (Cosmetic ? Practical ?)
On a 1600 X 1200 display and higher, it is very very difficult to see the dark red hairline defining the current frame.
Is there any possibility of doubling its width (maybe at high resolutions only), and / or making the color brighter ?
I use the curve editor extensively on video captures of scientific experiments exposures and the current line at high resolution, is causing a lot of eye strain (can barely be seen.)
Now, for a long due 'Thank you Phaeron' for implementing the feature of 'auto saving the Virtualdub main window dimensions & position.' I asked for this when I was a previous member of the forum (July 2005.)
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| phaeron |
| Posted: Jul 25 2010, 03:59 AM |
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What do you mean? I use 1920x1200, and I can see it just fine. 
Okay, seriously....
That seems like a reasonable request. Do you have any of the scaling parameters set in Windows, like the high DPI or large font setting? I'm wondering whether I should key this off of one of those, or if it needs to be a program-specific setting.
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