HDR Composition produces 'posterized' image?

[Josh Lake]

I was very excited to finally get my three master images of M42 H-alpha data together: 1 minute, 10 minutes, and 20 minutes. I used RBA's excellent tutorialas a guide, keeping the data linear.

Unfortunately, the resulting HDR image looks very posterized in the deep clouds surrounding the core. I suspect this has something to do with the 1 minute image, but perhaps it's a function of the 64-bit product. I tried a few things like excluding one of the images from the process, but I need that dim core for the image to be fully realized.

Here is the posterized result and the three source files, all auto-stretched. Yes, I know the 1 minute exposure looks pretty bad, but I was just hoping to use the core.

https://www.dropbox.com/s/n98g0tlxj3c5pzy/PosterizedHDR.png

Any thoughts?

[MikeWiles]

Hi,

The screen stretched image will look posterized because it's trying to render a 64-bit image, but the data itself is not actually posterized.  Test it for yourself.

1 - Click the A button on the Screen Transfer Function to auto-stretch the image.  The image will appear posterized.

2 - Drag and drop the screen transfer function onto the histogram transformation tool.

3 - Turn off the auto-stretch on your image and return it to displaying the data in its linear format.

4 - Apply the Histogram Transformation tool.  The stretched image will not be posterized.

I'm working on a similar image myself....so I dealt with this a couple of days ago.

Mike

[Josh Lake]

Ah, of course, this did the trick! Thanks, I should have just gone ahead. The data looks great.