Question: Is a 256 intensity level ramp test supposed to show Gradient Banding ?

Answer: 256 shades or colors will often show banding. Banding occurs when the video subsystem or display can reproduce enough colors or shades to smoothly go from one extreme to another.

Is the answer correct ?

I think you meant "cannot" rather than "can".

It is more complicated than 256 levels - that is only true of PC based signals. Video has different levels for B&W and color. Using video on PC means making sure you have right levels for intended usage.

Also some ramp tests are unavoidably dithered to avoid banding during mastering - so you have to know for sure which test patterns to use.

Question: Is a 256 intensity level ramp test supposed to show Gradient Banding ?

Answer: 256 shades or colors will often show banding. Banding occurs when the video subsystem or display can reproduce enough colors or shades to smoothly go from one extreme to another.

Is the answer correct ?

8-bit video should be able to avoid banding, basically, on real content. If you use a pattern with hard edges you can often see the steps individually, but these are unrealistic patterns.

So no, I do not agree with that answer. 8-bit video done properly should avoid visible banding.

edit: and what kras says, "cannot."

It's a greyscale 256 gradient Ramp (http://www.w6rz.net/ramp.zip) , from displaymate.
dr1394's 254 greyscale ramp aso shows banding.

By banding we mean that if you captured the digital data - it does not step up by 1 consistently (and this assumes your capture method is not harming the data) For some reason I do not have DisplayMate installed on the desktop- and it is worthless checking out DisplayMate on my laptop - portable video chips are not the greatest.

ask dr1394 he certainly should know if his pattern is clean.

If you have a sharp eye it may be possible to see the step up - you really are detecting the edge more than the brightness difference. This is why dithering can be very effective in hiding banding - it destroys the edges.

By banding we mean that if you captured the digital data - it does not step up by 1 consistently (and this assumes your capture method is not harming the data) For some reason I do not have DisplayMate installed on the desktop- and it is worthless checking out DisplayMate on my laptop - portable video chips are not the greatest.

ask dr1394 he certainly should know if his pattern is clean.

If you have a sharp eye it may be possible to see the step up - you really are detecting the edge more than the brightness difference. This is why dithering can be very effective in hiding banding - it destroys the edges.
My ramp pattern is clean in YCbCr space, but it definitely will have steps of 2 in RGB space. It's just a function of 8-bit YCbCr to 8-bit RGB conversion.

I do have the equipment to do a dithered pattern. I should give it a try.

Ron

That would be much appreciated, dr1394.

For a test detecting banding - you do not want a dithered pattern. You want to see the step up edges so you can detect if some don't step up or some have a double step up - meaning you have B&W or RGB level issues.

Any media is YbCr so RGB colorspace conversion can be an issue - best to have a clean RGB source as well so you can test both display paths.

Dithering is used sometimes in the mastering process and some test DVDs got stuck with it.

Thanks for clearing that up, krasmuzik.

Banding artifacts are Horizontal, and Dithering artifacts are vertical.

There is no directionality to banding or dithering - what gives you that idea?

Thanks for clearing that up, krasmuzik.

Banding artifacts are Horizontal, and Dithering artifacts are vertical.

huh? Banding can be in any direction. Dithering is completely different.

I didn't know that. I thought Banding was horizontal and Dithering was vertical.
Thanks for clearing that up.
Can you give me an example of vertical dithering ? :)

I didn't know that. I thought Banding was horizontal and Dithering was vertical.
Thanks for clearing that up.
Can you give me an example of vertical dithering ? :)

I don't know what you mean by "vertical dithering."

Dithering is just a method used to approximate value in between things. For instance as a crude example, if I have an on and an off position on a light switch and I want to dim the light, I can't actually dim the light but I can approximate halfway on by flipping the light on and off very quickly.

Dithering can occur temporally as in the lighbulb example (this is how DLP displays create an image), or it can also occur spatially by faking a smoother transition boundary than you might be able to achieve given the limited levels at your disposal.

Intelligent use of dithering in video or displays can help mask banding issues.

see also:
http://en.wikipedia.org/wiki/Dithering

Here's the dithered ramp. This was done by making a 10-bit ramp pattern and then using the built-in dithering on the HD MPEG-2 encoder capture silicon.
Not dithered:
http://img259.imageshack.us/img259/395/rampvz6.th.jpg (http://img259.imageshack.us/my.php?image=rampvz6.jpg)
Dithered.
http://img186.imageshack.us/img186/1769/ramptenfp5.th.jpg (http://img186.imageshack.us/my.php?image=ramptenfp5.jpg)

Ron

Here's the dithered ramp. This was done by making a 10-bit ramp pattern and then using the built-in dithering on the HD MPEG-2 encoder capture silicon.
Not dithered:
http://img259.imageshack.us/img259/395/rampvz6.th.jpg (http://img259.imageshack.us/my.php?image=rampvz6.jpg)
Dithered.
http://img186.imageshack.us/img186/1769/ramptenfp5.th.jpg (http://img186.imageshack.us/my.php?image=ramptenfp5.jpg)

Ron

dr1394,

Those images you've shown in the quote.
Would a .jpg show banding that a .png wouldn't ?
I mean does using .jpg introduce artifacts you wouldn't see if you used .png ?
Or is .png better for these images than.jpg ?

May I please ask for a non-dithered one that is a .png ? :)

For a test detecting banding - you do not want a dithered pattern.

Please tell me what a dithered pattern is good for. :)
Also, you say I should see the step up edges.
Where should I see the vertical lines on the images dr1394 posted ?

8bit video always has some banding somewhere.