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Topic: Dynamic range compression, the equivalent for pics (Read 5164 times) previous topic - next topic
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Dynamic range compression, the equivalent for pics

There are so many discussion, about how loudness war is bad etc...
People complain that music are these days "over compressed",
and some believe that music would always be better with no compression at all.

I  was wondering what would be the equivalent of "dynamic range compression" (wiki article) ,but applied to pictures.
I think I found. It's called "tone mapping",
and it's usually applied to HDR  pictures.
Here's one  example at flickr:
http://www.flickr.com/photos/elementalpaul...ol-89888984@N00

I  think it behaves in similar way to compressed audio:
* local details are over-emphasized (for compressed audio,  weak sound are amplified)
* the global contrast is more ore less killed . It looks overall "gray",
you can't say there's dark/bright areas (for compressed audio, dynamics are killed).
* artificial aspect.

When applied moderately , tone mapping can be used to emphasis local details , while still
preserving a natural aspect.
That's same thing for compressed audio. When Dynamic Range Compression is applied moderately, the result can still be interesting, and there's no point in wanting zero compression.

Dynamic range compression, the equivalent for pics

Reply #1 –
That's an interesting connection you have brought up. I've known about HDR for a while and I know that the music I listen to is compressed, but I never connected the two ideas. I think it's a good analogy, but I do not know the specifics of the signal processing done in each case, so I cannot comment on whether it is truly analogous. Food for thought, at the least. I've always thought that some songs, or parts of songs, with heavy compression sound pretty spiffy, but it can get a bit tiring for a whole album.

I agree that there is nothing bad about using compression, just as there is nothing bad about using HDR processing on a photo; it is simply a matter of preference. I do understand complaints about overuse, though. If you listen to a certain type of music that benefits from high dynamic range, the prevalence of compression as a production technique could be very aggravating. I listen to metal, so that's not really a problem for me.

Dynamic range compression, the equivalent for pics

Reply #2 –
Yeah, I thought of this connection a while ago. If you compare tone mapping to multiband compression (viewed with a spectrogram) it really does seem a bit similar.

The biggest conceptual difference is that dynamic range compression operates across the time domain while tone mapping operates on static images. Furthermore, dynamic range compressors are typically only used for real-time processing, while tone mapping is very offline. As a result, there's a vast asymmetry on the time axis with multiband compression which does not exist with tone mapping along either image axis.

You also typically don't see quite as wide a dynamic range on the frequency or time axis with music that you do with light intensity with photography, for a number of reasons. That makes the importance of a tone mapping scheme not quite as high.

Dynamic range compression, the equivalent for pics

Reply #3 –
@Axon
Quote
I listen to metal, so that's not really a problem for me.

The album "Death Magnetic" from Metallica ( I  belive this music is kind of metal) , was over compressed and some people didn't like this.  Anyway,  I'm sure there's a way to cripple any music with heavy compression.

@Muftobration
Quote
As a result, there's a vast asymmetry on the time axis with multiband compression which does not exist with tone mapping along either image axis.

I didn't see any theory about this, but I  think that most of the time music is naturally asymmetric.
When there's a percussion for instance, the loudness increase abruptly , and then decrease more slowly. And most of the time that the same for every sounds (abrupt increase, slower decrease).
Also when playing with a compressor (or else),  the "attack time" you use is usually inferior to "release time".

Quote
You also typically don't see quite as wide a dynamic range on the frequency or time axis with music that you do with light intensity with photography, for a number of reasons

?????  This might depend of the kind of music (I'm thinking of  classical music ... ), or the period of  time you use for evaluating the dynamic range.

Dynamic range compression, the equivalent for pics

Reply #4 –
Quote from: extrabigmehdi on
There are so many discussion, about how loudness war is bad etc...
People complain that music are these days "over compressed",
and some believe that music would always be better with no compression at all.

I  was wondering what would be the equivalent of "dynamic range compression" (wiki article) ,but applied to pictures.
I think I found. It's called "tone mapping",
and it's usually applied to HDR  pictures.
Here's one  example at flickr:
http://www.flickr.com/photos/elementalpaul...ol-89888984@N00

I  think it behaves in similar way to compressed audio:
* local details are over-emphasized (for compressed audio,  weak sound are amplified)
* the global contrast is more ore less killed . It looks overall "gray",
you can't say there's dark/bright areas (for compressed audio, dynamics are killed).
* artificial aspect.

When applied moderately , tone mapping can be used to emphasis local details , while still
preserving a natural aspect.
That's same thing for compressed audio. When Dynamic Range Compression is applied moderately, the result can still be interesting, and there's no point in wanting zero compression.


Do you have access to Photoshop? If so, go play with 'curves' which allows you to stretch and compress as you like. Doing white compress and black stretch (similar to 'gamma' applied to video to compensate for the non-linearities of the CRT) you'll be able to make all sorts of interesting changes without blowing out the highlights like the +4 stop example on the HDR page on Wiki.

G²

Dynamic range compression, the equivalent for pics

Reply #5 –
I've made digital photography/digital audio analogy before here and elsewhere, and I think it works great in many ways. Even when 14-bit RAWs were introduced, photographiles (they do exist, folks) were stoked, but some skeptical minds were like "why don't we just test it?". It was found that the 2 extra bits were "lost in the noise". There was NO more dynamic range at all, it was just basically a waste of space (it could be a bit useful by some method of stacking pictures that pretty much only astrophotographers use, which was akin to some kind of noise shaping I guess). The photographiles were seeing all kinds of "smoother gradients" and such in their photographs of their Canon 40Ds, than on the 12-bit 5D (which still gives better pictures due to the much larger sensor).

Sound familiar?

About DR, one difference is that in photography it is usually limited by the display or otherwise final medium, not by the capture itself. That's probably why DRC is much more useful in photography (or maybe I should say more widely acceptable).

Dynamic range compression, the equivalent for pics

Reply #6 –
Quote from: extrabigmehdi on
I  was wondering what would be the equivalent of "dynamic range compression" (wiki article) ,but applied to pictures.
I think I found. It's called "tone mapping",
and it's usually applied to HDR  pictures.

Hmmm... I've never much cared for HDR photography - it's intriguing, & certainly striking, but I've yet to see an HDR image I like enough to want to see again.
Your hypothesis may be testable with Photosounder. I've never used it, but it will create an image from a sound file. Get time matched samples from two mixes of the same track, one dynamic range compressed & one not, & compare Photosounder's output.

Dynamic range compression, the equivalent for pics

Reply #7 –
Quote from: southisup on
Hmmm... I've never much cared for HDR photography - it's intriguing, & certainly striking, but I've yet to see an HDR image I like enough to want to see again.
Your hypothesis may be testable with Photosounder. I've never used it, but it will create an image from a sound file. Get time matched samples from two mixes of the same track, one dynamic range compressed & one not, & compare Photosounder's output.

Too many people take too many liberties with HDR to get that fake look, but at least for me, the strength of HDR is when you don't notice it. These pics would have been impossible without it

http://photos.smugmug.com/photos/94303135_opQeP-L.jpg

http://photos.smugmug.com/photos/94303174_6B99m-L.jpg

As you can probably guess the first one was more difficult, but in both, you could either get some detail out of the window and have the rest of the room completely dark, or you could get the window completely "blown" and get the room bright enough. The light from the lamps also gets nicely blended.

Dynamic range compression, the equivalent for pics

Reply #8 –
As some have mentioned, there's a time dimension lacking in HDR - you want to give an increased perception of dynamic range at one instant in time, but otherwise it is a good comparison

HDR is very useful, and lets you take photos that would have been otherwise impossible. Sadly, lots of people fuck it up (just like with dynamic compression), giving HDR a very bad reputation.

A few examples of mine:
http://bighugelabs.com/onblack.php?id=3143...&size=large (a normal photo would have left the boat house wall in total shadow due to the light intensity from the sky)

http://bighugelabs.com/onblack.php?id=3316...&size=large (relatively detailed foreground despite the fact that the photo has been taken directly against the sun)
Thorbjorn

Dynamic range compression, the equivalent for pics

Reply #9 –
Remember that our ears have a much higher dynamic range than our eyes.  Dynamic range compression on images make a lot more sense because we can only see in a very narrow range of intensities at one time, this sliding window of intensities we can see is controlled by our iris, just like the aperture on a camera.

HDR photography is completely unnatural, a human would never see anything like that in real life, I think most of them look silly, like crap CGI that hasn't taken into account the properties of our eyes.  But still, if you have a real HDR photograph and you want a person to be able to see it all in one image then compressing the dynamic range is absolutely necessary.

However, if you have a piece of music which covers the full dynamic range of our ears (well, say 30dB to 100dB SPL) then you don't have to apply compression in order for a person to hear it all.

Dynamic range compression, the equivalent for pics

Reply #10 –
Quote from: Borbus on
Remember that our ears have a much higher dynamic range than our eyes.

I think that quoting entire post and adding "Yes!!" at the end would be a serious violation of netiquette and probably of forum rules, but this what I feel about Borbus' post. He or she made the most important points here.

The only thing I do not agree is "HDR photography is completely unnatural, a human would never see anything like that in real life". Actually, internally we do see like this: the internal image is composed from results of scanning with variable iris, so it's in a way similar to HDR.  But most of them look silly and "overdone".
Ceterum censeo, there should be an "%is_stop_after_current%".

Dynamic range compression, the equivalent for pics

Reply #11 –
I was just thinking the same thing about our eye's adjusting iris. When we look at some part of a scene, our eye adjusts to a comfortable light level and that is the light level at which we remember this part of the scene. We do this for each chunk of the scene and end up with a whole image composed of the smaller, light-adjusted parts. With a static image, this is not possible, since the light distribution is the same everywhere on the picture. I think the pictures hybris posted are good examples of a situation wherein using HDR allows us to get lighting consistent with a natural image; looking at the window would narrow our iris and looking at the dark side of the TV would widen it, so each was roughly the same.

Dynamic range compression, the equivalent for pics

Reply #12 –
hybris, very nice photos! Halos on tone mapped HDR images are annoying enough, but even worse is the software that makes regular non-HDR images look "HDR" by adding the same halos.

I like Enfuse for tone mapping HDR images as it doesn't cause halos most of the time:



I'd say that HDR tone mapping with severe halos would be the equivalent to audio DRC that operates just slow enough that you can hear the gain pump up and down with every beat, like if you use the vlevel plugin in FB2K with the look-ahead time set way too low.
 

Dynamic range compression, the equivalent for pics

Reply #13 –
Quote from: andy o on
Quote from: southisup on
Hmmm... I've never much cared for HDR photography - it's intriguing, & certainly striking, but I've yet to see an HDR image I like enough to want to see again.
Your hypothesis may be testable with Photosounder. I've never used it, but it will create an image from a sound file. Get time matched samples from two mixes of the same track, one dynamic range compressed & one not, & compare Photosounder's output.

Too many people take too many liberties with HDR to get that fake look, but at least for me, the strength of HDR is when you don't notice it. These pics would have been impossible without it

http://photos.smugmug.com/photos/94303135_opQeP-L.jpg

http://photos.smugmug.com/photos/94303174_6B99m-L.jpg

As you can probably guess the first one was more difficult, but in both, you could either get some detail out of the window and have the rest of the room completely dark, or you could get the window completely "blown" and get the room bright enough. The light from the lamps also gets nicely blended.

Thanks for posting those andy o, they immediately brought to mind Jeff Wall's View from an Apartment (last picture on page)(some background). Fits the principle of HDR, is worth more than one look, & even includes a time element!