8-bit color depth versus 16-bit color depth

[Ags]

I am a rank beginner and my very first attempts were processed entirely in GIMP, until I learned how to do the initial stretches in DSS instead. I knew that GIMP has less color depth, but I had no idea the effect was so drastic. Tonight I tried to do all stretching in GIMP and compare the result to my efforts in DSS (actually, half the stretching is done in DSS and I finish off in GIMP, so I'm not yet getting the full benefit of the DSS color depth).

Can you guess which one was processed entirely in GIMP? The GIMP version is admittedly just a quick effort to see the consequences of GIMP's 8-bit color, whereas the other image reflects the pinnacle (:-)) of my processing skills.

EDIT: I uploaded better crops of M27.

[steppenwolf]

16 bit certainly makes a huge difference over 8 bit - for my first year or so of imaging it had never occurred to me that saving my stacked data as .BMP files was diminishing my hard won work so much! That was a lesson well learnt I can tell you.

[Ags]

Looking at the detail in the image, I find it incredible that the photons retained this information over hundreds of light years. Space is REALLY empty.

[dph1nm]

Hmm - something must have gone wrong in the GIMP processing. Even with 8 bit, you should have 255 colour levels available in GIMP - your image only seems to have about 10. I have processed quite happily in GIMP and get images like your left hand panel. For display on the web there is really little difference between 8 and 16 bit processing.

NigelM

[Ags]

Yes GIMP does have 256 levels, but my image was very faint so it only made use of the bottom 10 levels.

The second image is also stretched in GIMP using the same procedures but was initially stretched in DSS, causing the image to use dozens more levels in GIMP.

[dph1nm]

Ah - OK. If you are going from DSS to GIMP you need to apply the DSS changes first I reckon. The problems is not really with GIMP processing, but in the transform of the initial file from 16bits to 8bits (which I guess is part of GIMP as well really). You can happily take (8-bit) jpgs straight from a camera and process them in GIMP and get perfectly reasonable images.

NigelM

[Luke]

It's amazing what a difference 16 bit makes!

I did start off with 16 bit, but even then I didn't even realise I had any data at first, because most of it was in the very low levels.

I thought I had nothing and gave up imaging for months! (imaging at F10 probably didn't help either - if I started again I'd try to use a small, fast ED refractor).

I then found some videos online showing the multiple curve adjustments on an image and the penny dropped that you can be really agressive and find tons of stuff in the low levels (as well as noise!...).

I did check out GIMP and really liked some things about it such as the curve adjustments, I think I heard they were working on a 16-bit version?

[Ags]

GIMP is now semi-16 bit... It loads images in 8-bit and saves them in 8-bit, but you can do all processing between those two points in 16-bit by enabling GEGL, an optional feature. Of course, you have already lost all your data the moment GIMP opened the image as 8 bits. But they are getting close to full 16-bit support.