16 bit support

[einstein]

Hi!

They say that GIMP 2.10 supports 16 bit images but when I import a 16-bit TIF to GIMP, it prompts a warning that it will convert it to 8 bit. I am confused. It looks like it didn't loose any smooth tonal changes but I'm not sure cuz I don't use any professional monitor.
Somebody could explain me what's up?

---

And another question, simultaneously.

I am a BIT confused about all these BIT depths. I can save a 16-bit TIF file in GIMP with JPEG compression. It seems that it keeps all smooth tonal changes but the file size is very small, like average 8-bit JPEG. Is is possible that 16-bit information is stored in such a small file? Of course some JPG-typical artifacts occur but the result ich still so much better than an usual JPEG. Lastly, could we alter the amount of JPEG compression within TIF format?

[rich2005]

The usual problem, not able to reproduce that from any of my 16 bit tiff images.

Can you give details of where you get the tiff files? Tiff has got so many different types and do you know the compression? If possible post an example (if not too large) on a file sharing site such as drop-box.

In Gimp 2.10.2 (Win10) you might get something like this https://i.imgur.com/NlD3Jhx.jpg but it opens as 16 bit.

A CMYK tiff does not open so the problem is not that.

Are you using the latest Gimp 2.10.2 for windows? The more information you give the better.

another answer simultaneously

The jpeg format is strictly 8 bit. That includes exporting a 16 bit image as a jpeg compressed tiff. There is a warning if you try that using Gimp. Like this https://i.imgur.com/phIGLVF.jpg
Ahh..re-read you are exporting the tiff as a jpeg. It will be 8 bit, quality is in the eye of the beholder. Just keep that as a finished product and use your 16 bit tiff for editing. In fact Gimp works better in 32 bit floating point so sometimes faster when you promote the bit depth.

[einstein]

I was exporting TIFFs from Lightroom, using LZW compression (I could also use ZIP compression), used sRGB and also ProPhotoRGB space (if that makes any change). Then imported them into GIMP and further edited.

I use GIMP 2.10.0 with Win7 64-bit. Will it open 16-bit file as 16-bit? Will it make any change if I upgrade to GIMP 2.10.2?

What's the difference between integer and floating point precision? I mean, I know it mathematically but how does it influence the image processing? 8 bit was always just 8 bit for me, the same goes with 16... 32 already sounds exotic.

Can I alter the amount of JPEG compression within TIF format?

[rich2005]

(06-10-2018, 11:25 AM)einstein Wrote: I was exporting TIFFs from Lightroom, using LZW compression (I could also use ZIP compression), used sRGB and also ProPhotoRGB space (if that makes any change). Then imported them into GIMP and further edited.

Is it just 16 bit tiff files from LightRoom that will not open (as 16 bit) in Gimp? Do you have any other applications to use. For RAW to Gimp there is both DarkRoom and RawTherapee applications. The Partha http://www.partha.com version of Gimp 2.10.2 includes NuFraw for importing RAW.

Quote:I use GIMP 2.10.0 with Win7 64-bit. Will it open 16-bit file as 16-bit? Will it make any change if I upgrade to GIMP 2.10.2?

I normally use GIMP in linux but keep a Win10 VM with Gimp 2.10.2 on it for Windows issues. Not a bad idea to update.

Quote:What's the difference between integer and floating point precision? I mean, I know it mathematically but how does it influence the image processing? 8 bit was always just 8 bit for me, the same goes with 16... 32 already sounds exotic.

Just what I read, Gimp works fastest in either 8 bit or 32 bit floating point. Working in 16 bit is ok but Gimp might be a little slower.

Quote:Can I alter the amount of JPEG compression within TIF format?

I do not know. Maybe you can, using say, ImageMagick. But that gives you a 8 bit tiff - why use that - export to a jpeg.

EDIT: A quick try with ImageMagick. Does not like Gimp made tiff's. An uncompressed tiff from delaboratory 96 MB compresses to 78 MB and opens in Gimp as 16 bit, which surprised me considering the Gimp warning. Trying to change compression, the usual quality setting had little effect, so probably not possible.

[einstein]

Ok, I just did upgrade to GIMP 2.10.2. But I'm not going to upgrade Windows, no way!

The only 16-bits I have come from Lightroom but I downloaded some sample image from web and it's just the same.

In the link there's a 16-bit TIF from Lightroom, compressed with ZIP algorithm, that I opened in GIMP. Forgive me but I'm still not sure if it can reproduce 16-bit depth.
One thing I know - if I import JPEG to GIMP and then export JPEG, there's vivid banding in sky area. If I import 16-bit TIF, the gentle tonal changes are much smoother. Anyways, I want to know if I'm dealing with 16 bits.

https://drive.google.com/open?id=1c7duxp...eavTUXqiZa

[rich2005]

Lets go back to the original question. Which 16 bit tiff files can you not open In Gimp 2.10.2 as 16 bit?

Quote:..They say that GIMP 2.10 supports 16 bit images but when I import a 16-bit TIF to GIMP, it prompts a warning that it will convert it to 8 bit. I am confused.

Not as confused as I am. The sample you provided opens in Gimp 2.10 as 16 bit so where is the problem?

Totally different question

Quote:One thing I know - if I import JPEG to GIMP and then export JPEG, there's vivid banding in sky area. If I import 16-bit TIF, the gentle tonal changes are much smoother.

Any image if you open as 8 bit - say a jpeg and edit. you lose data - get a 'combing effect' which can lead to that banding you see.

example 8 bit before and after https://i.imgur.com/3xJy6Aj.jpg see the gaps in the histogram - that produces the banding.

Use a 16 bit file reduces the effect. https://i.imgur.com/iUwzHQB.jpg

Even Ad*be says Open your 8 bit jpeg, convert to 16 bit for editing. Still not sure what you are doing and why the desire to use jpeg compression for a tiff.

Quote: Anyways, I want to know if I'm dealing with 16 bits.

Image -> Image Properties will tell you the precision of the image.

Back to which 16 bit tiff file does not open in Gimp 2.10 and where does it come from?

[einstein]

I was just curious what I'll get from JPEG conversion in TIF but now I see it leads to nowhere so let's forget about it.

I assume it must be something with my computer - I cannot open ANY 16-bit TIF file as 16-bit in GIMP. Neither these from Lightroom, nor samples from web. GIMP always converts them to 8bit, although I have the newest version now.

[mholder]

I think if you shared what you are trying to do, then it would help others understand.

One advantage of floating point values is that you can adjust the values beyond the clipping ranges and recover them.  This is helpful for adjusting things like exposure in photos.

Png files can also be higher bit depth.

Also, I think GEGL works in higher bit depth, as well as GMic. So the filters will be more accurate with less artifacts.

--edit. I did a test, saving a 16 bit tif file from Blender. Gimp 2.10 opened it as 16bit

[Ofnuts]

(06-10-2018, 10:00 PM)einstein Wrote: I assume it must be something with my computer - I cannot open ANY 16-bit TIF file as 16-bit in GIMP.

... and until you share one of these files with us, we will never know...

[einstein]

I shared the file form Lightroom a few posts above:

https://drive.google.com/open?id=1c7duxp...eavTUXqiZa