New article on color management

Started Apr 26, 2013 | Discussions thread
OP gollywop Veteran Member • Posts: 8,284
Re: Hope this may help a bit ...

Detail Man wrote:

gollywop wrote:

Hugowolf wrote:

gollywop wrote:

And, although the spaces are based on integer values, processing is done with floating point numbers.

In processors like RPP, Rawtheraee, and PhotoNinja, yes.  In ACR/PS, I don't think so.  Adobe still uses integer arithmetic as far as I know.  But I'd certainly be willing to be guided to documentation that says otherwise.

I would be surprised if it were otherwise. It is standard practice to map 0-255 to 0-1, it is just much easier to algorithmically process that way.

Surprise is indeed fun. But I'm waiting for documentation that supports the surprise.

Meanwhile normalizations do not require floating point.

Regarding the 2010 processing, Ken is a quite knowledgeable chap:

kenw wrote:

I'm really curious to watch what RT and RPP start to be able to do with floating point processing and cameras like the K5 which have incredibly low read noise compared to something like ACR/LR that uses fixed point algorithms optimized for speed.

Thanks, DM for that quote.  It is completely in line with my understanding about ACR/LR/PS that they used fixed-point calculations from the beginning to keep processing speed in check.  When they began writing PS, that was a real issue, and some platforms didn't even have FPU's in their basic models.  For a good period thereafter, the use of an FPU would have made the operation very slow, and there wouldn't have been anything like a reasonable response to the slider actions.

And, of course, once all that code became ensconced in the product, it would have been (and apparently still is) very difficult to change it.

The speed issue is still with us.  RPP and RT and PN are good examples of the kind of response one gets when using real floating-point processing.  People who are into their processing are willing to put up with the delays, but most people aren't, and I suspect Adobe is well aware of this attitude.

Regarding the 2012 processing, certain floating-point functionality (to some extent) exists:

... Lr 4.1 and ACR 7.1 have the ability to import and render floating-point HDR images.  Supported formats are TIFF and DNG.  (If you have HDR images in other formats like OpenEXR or Radiance, you can use Photoshop or other tools to convert them to TIFF.)  Supported bit depths are 16, 24, and 32 bits per channel.

If you're using Photoshop's Merge to HDR Pro feature to perform the "merge" step, be sure to choose 32-bit output in the top-right popup menu of the HDR Pro dialog box.  This will generate a floating point (but not yet tone-mapped) image, which you can then use ACR or LR to render and tone map using the new PV 2012 controls.

-Eric Chan, Reply #2 on: May 31, 2012, 09:44:14 AM

Apparently, when Eric and the other engineers work working on the V4 PV2012 develop module sliders, they used 32 Bit floating point HDR images to make sure there was sufficient slider capabilities. Then the finalized the basic module. After releasing V4 they realized the power was there for handling HDR 32 bit floating point files so they incorporated it into V4.1.

-dmward, 23rd of September 2012, Post 15

Eric Chan has informed me that there are two image-processing pipelines in Lightroom: output-referred, and scene-referred. Raw files get the scene-referred pipeline. Integer TIFFs get the output-referred pipeline. Therefore, the TIFF test images are getting a different set of processing than LR applies to raw files.

Yes, the HDR stuff was written de novo and has to use exponent-based numbers to deal with the necessarily wide number of DR stops that characterized HDR.  There is no way around it.  It is also the case that many of PS's "normal" features are simply not available when working in the HDR mode, not until you have done a final tone-mapping into a regular psd image.

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