Jump to content

Recommended Posts

Posted

Hi,

I'm sure there's a simple answer for this, but I'm still scratching my head after a lot of research ...

I'm using APh to stack astrophotography images - and it does a great job !

But - even though my original FITS are 16 bit RGB, APh opens them as 8 bit RGB.

So, the dynamic range is only 256, when it should be 65,536.

Maybe I'm missing something obvious ???

Thanks,

 

Gary

 

Posted

Thanks Lee,

OK - I've just uploaded a FITS for you.

If you select a white star, you'll see that it never goes past RGB = 255,255,255, and the histogram only displays up to 255 levels.

Other apps open this as 16-bit ???

Thanks,

Gary

 

Posted

RGB/16 still show values (depending on color chooser / info panel settings) from 0-1, 0-100%, 0-255.

The difference is that you have smaller steps. 
 

But you can proof the higher bit depth indirectly, using the procedural texture filter, or boosting brightness so that shadows start to show the higher resolution.

To check at your own:

  • open a RGB16 file
  • export as RGB8 file
  • place RGB8 file so positions match 
  • set blend mode to difference
  • add levels adjustment on top (not nested), and set white level to 1%
  • Now you see colors from the “lower bits”

If in contrast you do the same process starting with a RGB8 image, it will stay black.

 

RGB/16 is still capped at 1.0 - the data is stored as 16 bit integer and converted for display only.

Only if you use RGB/32 you can use values above 1.0, called unbound values in tutorials.

you can use the histogram and adjust min/max settings to check for pixels > 1.0

 

please note that Affinity Apps are currently unable to render the RGB/16 images correctly on screen. The rendering is limited to 8 bit. This has been raised as bug already. Never the less, the exports and files use 16 bit. 

 

Mac mini M1 A2348 | MBP M3 

Windows 11 - AMD Ryzen 9 5900x - 32 GB RAM - Nvidia GTX 1080

LG34WK950U-W, calibrated to DCI-P3 with LG Calibration Studio / Spider 5 | Dell 27“ 4K

iPad Air Gen 5 (2022) A2589

Special interest into procedural texture filter, edit alpha channel, RGB/16 and RGB/32 color formats, stacking, finding root causes for misbehaving files, finding creative solutions for unsolvable tasks, finding bugs in Apps.

I use iPad screenshots and videos even in the Desktop section of the forum when I expect no relevant difference.

 

Posted

Just to mention another bug affecting RGB/16: on Windows, the color chooser is broken when set to hex mode / 16bit resolution. It does not display the lower 8 bits, but repeats the upper 8 bit by mistake. Again, the data within the file are treated correctly, only the display of the color numbers in the color panel is bogus.

still unfixed in 1.10.5 retail.

Mac mini M1 A2348 | MBP M3 

Windows 11 - AMD Ryzen 9 5900x - 32 GB RAM - Nvidia GTX 1080

LG34WK950U-W, calibrated to DCI-P3 with LG Calibration Studio / Spider 5 | Dell 27“ 4K

iPad Air Gen 5 (2022) A2589

Special interest into procedural texture filter, edit alpha channel, RGB/16 and RGB/32 color formats, stacking, finding root causes for misbehaving files, finding creative solutions for unsolvable tasks, finding bugs in Apps.

I use iPad screenshots and videos even in the Desktop section of the forum when I expect no relevant difference.

 

Posted

Hi Gary, 

I've had a look at the file you supplied, so thanks for that.

I can see it's working internally at the correct bit depth and exports correctly too.

I see you have had previous discussions with @James Ritson on this <here> and  <this> comment may also help.

Besides that and the bug that @NotMyFault mentions I haven't really got anything to add but I've tagged James to see if he can add anything beyond what's been previously mentioned specific to astrophotography workflow.

Lee

Posted

Thanks Lee,

It's good to know that APh is treating the data internally as 16-bit, but the data presented to the UI is misleading ...

16-bit values are being displayed as 8-bit - so you can understand why users might get confused.

IMHO - all outputs in the UI - histogram, info panel etc - should display 16-bit pixel values as 16-bit, not as 8-bit.

A relatively simple thing to fix I would imagine.

Gary.

 

Posted
19 hours ago, Gary.JONES said:

should display 16-bit pixel values as 16-bit, not as 8-bit.

I am not at all certain that I want a display for each of the three colours to range from 0 to 65535 or 0 to FFFF. If this gets implemented I would like it to be an option in the Preferences.

Mac Pro (Late 2013) Mac OS 12.7.6 
Affinity Designer 2.5.7 | Affinity Photo 2.5.7 | Affinity Publisher 2.5.7 | Beta versions as they appear.

I have never mastered color management, period, so I cannot help with that.

  • 3 weeks later...
Posted
2 hours ago, Gary.JONES said:

Maybe ...

But this thing is this - AP is displaying a 16-bit number using a range of 0-255.

It's wrong.

Affinity is a bit inconsistent when displaying color values. Sometimes (color panel) it allows you to choose the format (% 0-100, 0-1, 0-255, 0-65636, float), sometimes you have only a limited or no choice (info panel, color picker). This is no bug. You could file a feature request. It would be a bug if the implementation deviates from design specification. If implementation deviates from your expectations it is a feature request. 

Mac mini M1 A2348 | MBP M3 

Windows 11 - AMD Ryzen 9 5900x - 32 GB RAM - Nvidia GTX 1080

LG34WK950U-W, calibrated to DCI-P3 with LG Calibration Studio / Spider 5 | Dell 27“ 4K

iPad Air Gen 5 (2022) A2589

Special interest into procedural texture filter, edit alpha channel, RGB/16 and RGB/32 color formats, stacking, finding root causes for misbehaving files, finding creative solutions for unsolvable tasks, finding bugs in Apps.

I use iPad screenshots and videos even in the Desktop section of the forum when I expect no relevant difference.

 

Posted

That is just so totally not right.

If an app displays a number as 250, it should mean 250, not 64,250.

It violates the basic rule of UX - you need to be able to trust that what the computer tells you is correct.

In this case, it just isn't.

That's not a feature request - it's a design fault.

 

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
×
×
  • Create New...

Important Information

Terms of Use | Privacy Policy | Guidelines | We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.