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Can't get the hang of it!

Herzy

By Herzy
in Getting Started With Imaging

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Herzy

Herzy

Posted
Posted

Really sorry for spamming the posts recently. I just simply can't get the hang of processing my photos. I just made a thread about my 21 x 30s of M42. I couldn't process it well, but I have watched quite a few tutorials and I think I understand how to stretch an image. 

I took my stacked image of M81 (60 x 30s) and attempted processing. I first aligned the RGB channels, easy-peasy. As far as I understand, your supposed to stretch an image by dragging the greypoint to the left and dragging the blackpoint to the edge of the histogram. You do this process repeadetly until you get the spikes/lines in your histogram.

I did exactly this. I couldn't even do the process once before I got those lines. Do I not have enough data? 30 minutes of exposure time should surely be enough to do some work on the image. After my best attempts at processing I could barely see the spiral arms of M81. Any help is greatly appreciated! :)

-Hayden

 

image.jpeg

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Atreta

Atreta

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can you post the stacked unstretched tiff? I'd like to have a go at your image,  others will be able to give you more insights. 

maybe one dumb though of mine,  did you use both levels and curves? 

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bottletopburly

bottletopburly

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Yes I feel your pain , I find ps very time consuming so now have ditched that and use startools , I seem to get a half decent image may not be brilliant but im happy with it and it certainly easier to get too grips for me anyway than ps was , dropbox your file onto this thread maybe someone will see what you have 

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wornish

wornish

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Not sure what software you are using.  If its Photoshop then when using Curves to do the stretching be aware that the histogram does not fully update after each stretch and you can get the spikes and lines in your histogram.

even after moving the black and grey point sliders the first time, remember to click on the histogram refresh button .See pic below.

 

It might be in different places depending on the version of PS you are using.

Also don't overdo the stretching especially the black point.  Move it very slightly left for each stretch.  If you get too close to where  the graph starts to rise then it will clip your blacks and you will loose detail.  Looking at your example it seems that might be what you are doing.

 

It is best to do very small movements in each step, the temptation is to try and do the stretching in big steps.

 

refresh.jpg

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ollypenrice

ollypenrice

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Moving the grey point slider to the left in Levels is exactly the same as applying a logarithmic stretch in Curves. Curves, though, allows you to shape a custom Curve yourself. The Levels stretch always produces the same shape of curve. For a beginner the Levels stretch is a perfectly good starting point.

During the stretching process any slight imbalance in the colour will be exaggerated so after each stretch you should check the three separate colour channel histograms and keep the top left of each peak aligned to the same point. This is a good rule of thumb, not a religion. (Note that your image is very blue now.)

levels%20aligning-M.jpg

In bringing in the black point be very careful not to go too far. Most beignners do over clip.

Good:

healthy%20histogram-M.jpg

Black clipped:

unhealthy%20histogram-M.jpg

Olly

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The Admiral

The Admiral

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3 hours ago, bottletopburly said:

Yes I feel your pain , I find ps very time consuming so now have ditched that and use startools , I seem to get a half decent image may not be brilliant but im happy with it and it certainly easier to get too grips for me anyway than ps was , dropbox your file onto this thread maybe someone will see what you have 

I've not used PS but I have also gone down the Star Tools route. You can download a free trial that isn't time limited and allows you to have a practice. The only thing you can't do is save. If you elect to buy, it is very reasonably priced. Why not give it a try? There's a help forum as well. See http://www.startools.org/

Ian

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Herzy

Herzy

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8 hours ago, Atreta said:

can you post the stacked unstretched tiff? I'd like to have a go at your image,  others will be able to give you more insights. 

maybe one dumb though of mine,  did you use both levels and curves? 

I'll post it when I get home tonight. Yes I tried curves, but I had even less of an idea of what I was doing.

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