HDR for video: An Idea for a new filter

[cid_xvid]

I don't know programming. Please excuse me for that, as I can't make a filter for that.

But I was reading about HDR technique for photographies, when I saw this tutorial: HDR from 1 JPG (http://flickr.com/photos/cleever/255026221/).

Inmediately I thought if it would be possible to develop a filter that uses this technique for videos. There is a lot of information on the net, but using raw files (it has information like contrast that you can't find in a video). Anyway you can do something by darkening and brightening the image, and combining it with the original source into a single image.

Perhaps I have said something stupid, I just wanted to give the idea.

And forgive my english. See you.

[Adub]

It's (sort of) been done before.
Here is the link if you want it.
http://forum.doom9.org/showthread.php?t=93571&highlight=hdragc

[cid_xvid]

Excuse me, I made a search before and I didn't find anything. Doom9 forums are very big... :(

Thanks Merlin7777.

[MfA]

To me it seems more like histogram equalization with a bloom filter than anything to do with HDR.

[Adub]

MfA, you are right. A true HDR filter gives a picture (or pictures) that glow to it, which looks sooo cool. HDRAGC is more to bring a picture back to normal following the logic of the human eye.

Cid_xvid, what exactly were you planning on doing to create such a filter? Do you have an idea for parameters, possible output samples, etc?

[cid_xvid]

No, the truth was the histogram equalization. I was planning something like hdragc, a false hdr.

Thanks a lot for your replies :)

[Wilbert]

No, the truth was the histogram equalization. I was planning something like hdragc, a false hdr.
Could someone tell me the difference between a false (as in hdragc) and a good hdragc?

[communist]

I'm not sure either what they mean with true or false. What all those HDR 'filters' (software) do is combine the levels. The original link describing the "HDR from 1 JPEG" is pretty much what HDRAGC does in a different way:
HDR from 1 JPEG: brighten up image, then selectively darken it
HDRAGC: selectively brighten up image

Result is the same. Neither adds a glow - which you might be confusing from HDR in games where this is an overdone effect lately ;)

For 'real' HDR images you would either need a device capable of capturing a higher range or capture repeatedly with different f-stops. The first being rather expensive (in case of video) and the 2nd rather impractical if you plan on shooting more than solid stones ;)

[Mug Funky]

HDRAGC is "false" HDR because it tries to compress the dynamics to give the illusion of a greater than 8 bit dynamic range.

a true HDR would be 32-bit float pics, or even Cineon images (10-bit log).

you could always get HDR by shooting in 35mm...

[Alain2]

But HDR pictures shown on the specialised websites are all about playing with local levels to increase dynamic contrast, as hdragc but maybe with slightly more sophisticated algorithms.. ? So the difference with "true" hdr is only about that and the precision you achieve in pixels colors (>8 bits where hdragc stay at the same depth as the input) or there something more to it ?

[Mug Funky]

no, HDR is meant for a different thing entirely - the local contrast, dynamic compression thing is a bonus, meant as a nicer way of displaying HDR images on a LDR output device like a computer screen.

High Dynamic Range images are different from regular ones because they attempt to sample the entire range of RGB intensities. if you had a HDR image of a sunset, theoretically you'd be able to turn the brightness down until you could see an orange sun (rather than a large area of pure white with a sun somewhere in the middle, but completely washed out). and in theory you'd also be able to brighten the picture until the silhouetted face in the foreground shows enough detail that you can see colour in the eyes that were completely black before.

the challenge of algorithms such as the one HDRAGC is based on is getting all of that detail to be visible on the one screen, in as nice a way as possible (gamma correction helps, but will make everything look super-dull, very grey, and it'd be hard to spot certain things even if they are represented in that dull grey mud).

the avisynth plugin simply performs that kind of scaling on an 8 bit input image, as there's no rule to say you can't use the same technique on a LDR image if you just wanted a certain effect.

[edit]

btw, HDR images are usually created by taking a series of LDR pics at different exposures and merging them into a 32-bit floating point image. the original intention was to be able to make computer generated objects fit seamlessly into real-world situations. they're extremely useful for reflection maps, as even very small amounts of reflectivity will give white specular highlights where ordinarily you'd get a rather boring and ugly grey.

[Alain2]

Ah ok, thanks for the explanation Mug Funky :)

So what I understand is that HDR are pictures you create from the source with the correct sensors / equipment / tricks (different exposure merged into a higher bit depth), and that using hdragc on a normal frame (like a dvd source, yv12) is not hdr, is just playing with levels but the information available in the input is too low to get anything useful.

Also you say for HDR that you turn down / up the brightness so that you get to see details in the whole RGB that were not visible at human range, but later you talk about gamma correction.. is gamma correction (thus dynamic contrast) part of the HDR process or is HDR only about shifting (offsetting) up / down brightness to make part of the pictures more human visible without touching the contrast linearity ? From HDR pictures on websites, it looks to me that contrast linearity is well changed as well, like an unsharpmasking on a high radius... ?

[Soulhunter]

This (http://en.wikipedia.org/wiki/High_dynamic_range_imaging) explains it very good i think... ^^

And as we already talk about HDR video, have a look here! (http://www.brightsidetech.com/)


Bye

[Alain2]

Ok completely understand now. Tone mapping is something I do a lot on regular yv12 anime content, but it's not HDR, and neither is HDRAGC, it's just trying some clever tone mapping. Thanks for the link Soulhunter (should have googled myself, silly me ^^), it cleared up what I didn't fully grasp in Mug Funky explanation :)