Saving color space in EXR 32-bit HDR files

[Roland Wooster]

After creating 32b HDR files I'm trying to export them to EXR format. However it seems impossible to save a color profile with the file. Irrespective of what color profile I change the file to because the profile isn't saved with the file when I open it back up in Affinity it assumes ROMM and the colors get changed. 

Likewise, if I open the EXR file in the "HDR+WCG Viewer App" from the Microsoft store, it assumes that because there is no color profile saved in the file it must be sRGB, so only if I first convert the file to sRGB do files then open with the correct color in the HDR+WCG Viewer - because it assumes missing profile means sRGB. However of course if I instead open that same file in Affinity it looks horrible because it assumed EXR files are in ROMM. 

This problem seems unique to EXR files, things work correctly for me in TIFF and JPEG (albeit without the HDR support). 

Roland.

[Dan C]

Hi Roland Wooster

I've been looking into this and as far as I can tell EXR doesn't support embedded ICC profiles as part of it's default spec - see here

When opening an EXR file created in Affinity from any app the image will automatically be assigned the 'Working' colour space for 32bit images. If you don't want your EXR image to open in ROMM in Affinity Photo then please open Preferences>Colour and change the 32bit Colour Profile here to your preferred profile choice.

Now when re-opening the EXR in Affinity Photo you should find it's assigned the correct colour space. I hope this helps!

[Roland Wooster]

One of my expectations of True HDR images is increased luminance, contrast, and color gamut. It sounds like EXR is useless in being able to increase color gamut if every app will launch the EXR files in their own preference of color space because it contains no useful profile data to indicate otherwise. This limits you to sRGB for "safe" sharing. Meeting only 2 of my 3 basic expectations for HDR images. Does any other format work better? Does the Radiance HDR format suffer the same or similar problems?

[walt.farrell]

6 hours ago, Roland Wooster said:

One of my expectations of True HDR images is increased luminance, contrast, and color gamut.

I'll start by saying I have little experience with 32-bit color images, and none with EXR or HDR.

But I'm somewhat confused, and your statement of your expectation has enabled me to at least understand and express part of my confusion. So, thanks

It's all well and good to want increased luminance, contrast, and color gamut. I'd like that, too. However, what do you plan to do with your images? Can you print them with today's technology and get those benefits, or are they just for displaying on a monitor or video screen?

If it is simply for displaying on monitors or video screens, will you display them in one location, with known hardware, or will they be distributed for display elsewhere? Will those other locations have the appropriate hardware to display them properly?

What application will be used to display them? As you've said, without an ICC profile you can only hope that whatever application someone uses, it will display the images in a compatible way, always assuming the other user has a compatible monitor.

It seems like there is strong risk, today and sometime into the future, of producing a beautiful image that only the image creator can view properly.

[Roland Wooster]

For HDR I'm only seriously interested in digital display, paper lacks sufficient dynamic range. 

I plan to display the images on lots of different people's HDR displays, with unknown hardware. The other locations will have appropriate HDR hardware and HDR decoders, but the hardware in each case will have different ranges of luminance, color gamut, and contrast. The local device will tone map the image to a suitable displayable range. This is how HDR works today with HDR video, and we're on the bleeding edge of actually get TrueHDR working for photos (please dismiss the last decade's Fake-HDR that everyone is familiar with as "HDR" which isn't HIGH Dynamic Range, but rather COMPRESSED Dynamic Range). 

Today there aren't many HDR still image viewing applications, Affinity Photo is one, the "HDR + WCG Viewer" app in the Microsoft Store is another (free) viewer app. More are coming and we're working with the major browser vendors to implement HDR static image format support in the leading web browsers, once that starts then we'll really be in business. 

The "Strong Risk" you mention is exactly the current situation, if you lack the ICC profile you're going to be in trouble, but I'm told that can be solved by either embedding the profile in the image (makes the image file larger) or by ensuring people are aware of the need to load the profile. However, the problem right now is that EXR files (one of the few formats to actually support HDR) appears to lack the ability to define the ICC profile. Affinity defaults to assuming ROMM (when loading 32bit images) and the HDR+WCG-Viewer assumes sRGB if not defined. 

Thus, even with these two applications, unless I reduce my default color space to sRGB in Affinity for 32b images (I would guess less than 50% of ROMM color space) then any EXR image will have the wrong color space in at least one of the two apps I'm using, or possibly both if I was to save the image into a third color space!

Hence my conclusion, EXR isn't yet ready for prime time, if my HDR images can only benefit from luminance and bit depth improvement we're leaving one important vector of HDR benefit on the table, that typically with HDR the color gamut is also increased. 

If you want to learn more about the state-of-the-art HDR for the PC please take a look here, this is the VESA DisplayHDR website:

http://www.displayhdr.org 

We also have a list of certified HDR displays from the top display vendors on the website, on the "Certified Products" page. 

Roland.