High Dynamic Range (HDR) imaging

[MarkS]

I experimented with an HDR merge last Autumn to show the full moon and Comet Holmes in the same image with full dynamic range.  That's the easy part.  The difficult part is then creating a JPG from the HDR that looks anywhere near sensible. 

In theory an HDR image would be great for the high dynamic range of M42 (Orion Nebula) but, in practice, I think it is well nigh impossible to get a nice looking JPG from it.

[Mike]

I experimented with an HDR merge last Autumn to show the full moon and Comet Holmes in the same image with full dynamic range.  That's the easy part.  The difficult part is then creating a JPG from the HDR that looks anywhere near sensible. 

In theory an HDR image would be great for the high dynamic range of M42 (Orion Nebula) but, in practice, I think it is well nigh impossible to get a nice looking JPG from it.

Why? Does it look fine after processing but then change once converted to JPG?

[MarkS]

Mike,

HDR images:  Problem is not JPG.  Problem is compressing 32 bit image down to 8 bit image whilst preserving detail in both bright objects and dim objects.

Mark

[Daniel]

I use HDR's in the work I do, they would be great for using as a HDR where you can ramp the exposure up and down to show different levels of detail (M42 and M31 especially) but once you drop them down to an 8 Bit per channel image You'd basically be back to where you were before using the HDR, one advantage would be you could output images at different exposures to show different levels of detail, but it's best if you keep it as a HDR, would be interesing to see if there are any browser plugins that would support ramoing up and down of the exposure levels embedded in a hdr.

by the way, which method and software are you guys using for deconvolution? I had a look in IRIS for it but it seems you have to access it all through the command line

[Mike]

Yes but if it looks fine on the screen in the native format then it can be compressed respectively. What about using compressed TIFF instead of JPG? Or using less compression?

haven't tried HDR yet so no idea if I am making any sense.

[MarkS]

Mike,

Daniel's explanation is the best.  With HDR, within Photoshop, you can interactively ramp the exposure up or down to show different levels of detail (it's really cool!) but you can never display all levels of exposure simultaneously - even within Photoshop.

You have BIG problems dropping to 8bit.

Mark

[Rick]

This sort of thing --> http://www.flickr.com/photos/dmmaus/2451760682/
which explains this --> http://www.flickr.com/photos/dmmaus/2448144859/

(I've split this out of its parent topic, 'cos hopefully it'll be eassier to follow that way.)

[Mike]

I don't get that! According to this - http://www.cambridgeincolour.com/tutorials/high-dynamic-range.htm - you can convert to 16 bit and these images - http://www.smashingmagazine.com/2008/03/10/35-fantastic-hdr-pictures/ - are all HDR and look great to me !

[MarkS]

(I've split this out of its parent topic, 'cos hopefully it'll be eassier to follow that way.)

That dashes my hopes of making my Deep Sky Camp thread the longest and widest ranging ever!

Mike,  your first link sums it up when it says:
"Good HDR conversions therefore require significant work and experimentation in order to achieve realistic and pleasing final images."

[Rick]

That dashes my hopes of making my Deep Sky Camp thread the longest and widest ranging ever!

The Evil Moderator strikes again! (Wide-ranging is fine in Chat, but in the more technical sections a little more focus helps a great deal.)

significant work and experimentation

I expect DMMaus's comment about having "converted to 8-bit using local adaptation and a custom toning curve" probably glosses over quite a bit of twiddling...

[Rocket Pooch]

I experimented with an HDR merge last Autumn to show the full moon and Comet Holmes in the same image with full dynamic range.  That's the easy part.  The difficult part is then creating a JPG from the HDR that looks anywhere near sensible. 

In theory an HDR image would be great for the high dynamic range of M42 (Orion Nebula) but, in practice, I think it is well nigh impossible to get a nice looking JPG from it.

Sounds like a challenge, can I have a copy in photoshop CS.

[MarkS]

I'll see if I can dig out the HDR version.  Trouble is, I can't open it any more - my trial licence expired.

The image in this thread http://forum.orpington-astronomy.org.uk/index.php?topic=2755.msg10956#msg10956  was actually the earlier non-HDR version - I had to apply a very severe dynamic range gradient to get it to look like this.  Everything in the image is genuine i.e. I didn't use any "tool" to create lens flare - it was recorded by the camera.

[Daniel]

Have a look at HDRshop http://www.hdrshop.com/ version 1 is free and was developed by paul debevec one of the godfathers of HDRI

[Mike]

So, like I thought, you can have a 16 bit HDR image. It is only when converting to jpeg it drops to 8 bit as it is an 8 bit format anyway.

[Rick]

Today's APOD is a nice example: http://antwrp.gsfc.nasa.gov/apod/ap080808.html

[Mike]

Nice. Reading the bumpff on his website though it looks mor elike a masked composite than a true HDR merge.

That FITSWORKS software looks interesting.