19 replies to this topic

[dcaponeii]

Mike pointed out yesterday that one of my shots taken with the 12" Meade and the G26 camera was looking posterized so with this image from this morning I thought I'd try and confirm if it was something I was doing by reducing the color space to 8-bit.

 

This image has been reduced in size without changing the color depth.  I know it looks a little purple but It was only 45 minutes or so before sunrise and there was a substantial sky background that I've not properly dealt with.

 

 

In the next panel is the same image but resized to a different amount because reducing the color depth allows it to fit within the CN limits.

[dcaponeii]

Here is the same image as above but with reduced color depth.

 

 

I'm asking for help because I don't see the posterization on my monitor (1080p) but this isn't the first time.  Mike has seen it with his good monitor and Daryl saw something similar in one of my Jupiter images where I had cleaned up a sharpening line in the background that I couldn't see on my monitor.

[dcaponeii]

As a comparison, because Mike had mentioned that he thought I had saved as a JPEG file, I've done the same size reduction as above but saved the file as a JPEG.  I had to make a small reduction in quality to meet the CN limits.

 

[dcaponeii]

I've been also operating the camera using Firecapture since it has a much better automatic capture tool than the Orion software has.  Here is a later image just before I called it a morning.  PNG saved with the full 16-bit color depth and reduced to fit within the CN limits.

 

[Borodog]

Don,

 

What are you writing these out from? Every one of those images is heavily posterized. None of them is 16 bit. The 1st and last are 8 bits per channel i.e. 24 bit PNGs. The 2nd one is reduced to 5 bits per channel for better compression but obviously still in a 24 bit PNG container. The jpeg is also 24 bit of course but also heavily posterized.

 

It is not reducing to 8 bits per channel that is the problem. 8 bpc = 256³ = 16.8 million colors, which is adequate. What I see in these images is a tremendously reduced gamut of colors. I see brown, maroon, and charcoal. And that is it.

 

So the question is, where along the processing chain is this occurring?

[dcaponeii]

Don,

What are you writing these out from? Every one of those images is heavily posterized. None of them is 16 bit. The 1st and last are 8 bits per channel i.e. 24 bit PNGs. The 2nd one is reduced to 5 bits per channel for better compression but obviously still in a 24 bit PNG container. The jpeg is also 24 bit of course but also heavily posterized.

It is not reducing to 8 bits per channel that is the problem. 8 bpc = 256³ = 16.8 million colors, which is adequate. What I see in these images is a tremendously reduced gamut of colors. I see brown, maroon, and charcoal. And that is it.

So the question is, where along the processing chain is this occurring?

Interesting question. I’ll start leaving stuff out and see. What do you see after uploading to CN with your images? Con’s? Maybe the problem in with Paint Shop? I’ll spend some time on it in the am. Thanks

[Borodog]

Interesting question. I’ll start leaving stuff out and see. What do you see after uploading to CN with your images? Con’s? Maybe the problem in with Paint Shop? I’ll spend some time on it in the am. Thanks

I've done the re-download test on my uploaded images and they are identical to the files I uploaded, right down to the file size and "Difference" test (i.e. I load the re-downloaded image as a layer on top of the original and subtract it, with the result being 0 everywhere), as long as I first reduce them to < 1600x1200x500 KB. You can upload large files to your gallery, but if they are larger than 1600x1200, CN will reduce them to 1600x1200 and then all bets are off as to what it is doing.

[Borodog]

And once again, I highly recommend paint.net for creating your 8 bit images, both png and jpeg. It does a great job.

[dcaponeii]

Made another go at the image in question.  I subtracted the background away from the un-sharpened stack before anything other processing.

 

 

The histogram looks better but I still think I'm generating what Mike is calling posterized images.  It's clearly different from the subtle colors in his latest recovered mosaic and Con's color Moon's as well.  UGH

 

 

[dcaponeii]

And once again, I highly recommend paint.net for creating your 8 bit images, both png and jpeg. It does a great job.

I tried to go to paint.net and got to a website naming site instead.  It must be something different than paint.net.  Have you got a link?
 

[Borodog]

It’s free from the Microsoft store. Never use it as an intermediate step, only the last touch on an image before converting to 8 bit. It does not support 16bit output (which is a shame).

[Borodog]

By the way, looking closely at the latest image on my phone, I don’t see any obvious posterization. Certainly no maroon in the image. Maybe that is just the background subtraction. When I get in to work I’ll check on my monitor.

[Borodog]

Really good libration, by the way.

[dcaponeii]

By the way, looking closely at the latest image on my phone, I don’t see any obvious posterization. Certainly no maroon in the image. Maybe that is just the background subtraction. When I get in to work I’ll check on my monitor.

I appreciate you putting in the time to check.  I'm not even sure Wavesharp will output 16-bit color.  Paint Shop lets me increase the output to 16-bit color and that is usually greyed out if the image is already 16-bit.  I'm also wondering if you realize just how undersampled these images are.  The camera is 3.76 micron pixels and I'm imaging at f/5.  That's only 1.33x pixel size.
 

[dcaponeii]

It’s free from the Microsoft store. Never use it as an intermediate step, only the last touch on an image before converting to 8 bit. It does not support 16bit output (which is a shame).

$9.99 according to my computer.
 

[Borodog]

Do not pay that. It is free. Let me find the link.

[Borodog]

https://www.getpaint.net/download.html

[dcaponeii]

https://www.getpaint.net/download.html

Thanks

[Borodog]

I appreciate you putting in the time to check. I'm not even sure Wavesharp will output 16-bit color. Paint Shop lets me increase the output to 16-bit color and that is usually greyed out if the image is already 16-bit. I'm also wondering if you realize just how undersampled these images are. The camera is 3.76 micron pixels and I'm imaging at f/5. That's only 1.33x pixel size.

I don’t see any posterization in that last image on my work monitor.

[dcaponeii]

I don’t see any posterization in that last image on my work monitor.

That’s a relief for sure. Thanks for confirming. I guess it was not removing the background and that reduction to 32K color.