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Thread: Two ways to do the same thing.

  1. #1
    arith's Avatar
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    Two ways to do the same thing.

    I tried a method hinted at by Colin to take a lot of under exposed images and stack them, but since I am totally confused by why the method is used, why not just stack copies of the same image, apart from obviously noise being hidden by opacity the under-exposure bit leaves me a bit confused. I tried the formula of 1/L where L is the Layer base being 1 but I didn't have enough images to raise exposure sufficiently, so I used 100%, 75%, 50% with screen blending on the top two.

    Another problem is I can't work in 16 bit with layers but the HDR is all 16 bit, so which is better and can anybody explain how it is supposed to be done. cheers.

    Two ways to do the same thing.

    Two ways to do the same thing.

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    Moderator Dave Humphries's Avatar
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    Re: Two ways to do the same thing.

    Quote Originally Posted by arith View Post
    ~ can anybody explain how it is supposed to be done. cheers.
    Hi Steve,

    Pending Colin awaking from his beauty sleep; from memory I think it should be 100%, 50% and 33% for blending 3 pics. I think I remember this because to me 100, 50, 25 or 100, 66, 33 would have made more sense.

    The reason not to do it with same image is that the noise being random, averages over different exposures to zero, but would add if same image used repeatedly.

    OK that's me exhausted by scant "knowledge"

    Cheers,

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    arith's Avatar
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    Re: Two ways to do the same thing.

    Yes I know but it was too underexposed and I only did 3 images, but interestingly I only cloned out one dust spot in the top and non in the bottom. The top is without noise reduction at all, but is sharpened in DPP however the bottom HDR is processed normally all 16 bit until saving as jpeg. cheers

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    Re: Two ways to do the same thing.

    Quote Originally Posted by arith View Post
    I tried a method hinted at by Colin to take a lot of under exposed images and stack them
    Hi Steve,

    You've got the stacking bit right, but not quite sure where you got the "under-expose" bit from? Mostly it's a technique for (a) simulating a long exposure (where the simulated exposure is equal to the sum of all the actual exposures) or (b) a way of reducing noise from high-ISO shots where (very) roughly you need to double the number of shots for each doubling of the ISO.

    In terms of stacking, Dave was spot on - opacity (starting from the bottom) is set to 100% - 50% - 33% - 25% - 20% - 17% etc.

    As an HDR technique you need to expose for the highlights as per usual - take a bunch of shots - reveal the detail with fill light - then stack them.

    Does this help?

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    arith's Avatar
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    Re: Two ways to do the same thing.

    No it doesn't help ;D not really but minor points like what should be the blending,. Actually I thought I mentioned 1/L where L is a layer number but I can't see how to blend it and the only thing I found from suck & see was screen. How many for one ev is another thing.

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    Re: Two ways to do the same thing.

    Quote Originally Posted by arith View Post
    I can't see how to blend it and the only thing I found from suck & see was screen. How many for one ev is another thing.
    Hi Steve,

    Assuming that you're using Photoshop then you just change the layer opacity. Are you using Photoshop?

    I'm getting confused now!

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    Moderator Dave Humphries's Avatar
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    Re: Two ways to do the same thing.

    Quote Originally Posted by Colin Southern View Post
    Assuming that you're using Photoshop then you just change the layer opacity. Are you using Photoshop?

    I'm getting confused now!
    While Steve is getting his beauty sleep ...

    I'll chime in with the fact he has Elements, which I think can do this..

    Cheers,

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    Re: Two ways to do the same thing.

    You can't import different images into PSE unless I've missed something, I chose screen since it increased the exposure and I used Gimp. But should have used normal and a lot of images. cheers

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    Moderator Dave Humphries's Avatar
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    Re: Two ways to do the same thing.

    Quote Originally Posted by arith View Post
    You can't import different images into PSE unless I've missed something,
    Hi Steve,

    It's a while since I have done this, but you just open multiple pictures one after another, then, with the filmstrip visible at the bottom, drag and drop subsequent images onto the first (in main window), as you do this, I think it knows to add them as new layers and offers a dialog to name (each) new layer. I agree, it's not obvious!

    Then play around with blending, etc., but I don't know how to do that.

    Once you have one file with the others stacked as layers, go back and close the other donor images, or your computer may struggle with memory and slow down (also don't try this while you've got other stuff running like streaming internet content).

    Cheers,
    Last edited by Dave Humphries; 18th April 2010 at 10:22 AM.

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    Re: Two ways to do the same thing.

    Cheers; It certainly isn't obvious I will have a go.

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    Re: Two ways to do the same thing.

    Here is another stupid question maybe Dave will know the answer to; how do you line the layers up since the images are stacked as thumbnails. As you can see I'm not very good at manual lining up.

    Two ways to do the same thing.

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    Moderator Dave Humphries's Avatar
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    Re: Two ways to do the same thing.

    Quote Originally Posted by arith View Post
    Here is another stupid question maybe Dave will know the answer to; how do you line the layers up since the images are stacked as thumbnails. As you can see I'm not very good at manual lining up.
    Sorry, no, I don't know as I wasn't using it for this technique last time.

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    Re: Two ways to do the same thing.

    I'll just add the reason I'm doing it is as experiment to reduce CA by underexposing the highlights. It is a very bright day and with this lens I expect 1.5 pixel CA around the plinth. HDR does help but CA is recorded and it is hard to tonemap it out. The shots are 100iso f5.6 1/4000 or as wide as I can get it.

    If you didn't already know this is why the aperture is wide as possible .
    http://www.photozone.de/canon-eos/15...review?start=1

    Just had a very close look, don't know why I didn't do that until now since the whole point is to see if I can reduce CA, and the top image hasn't got much CA whilst the HDR although looking better has both red and blue CA.

    Looks promising.
    Last edited by arith; 18th April 2010 at 01:06 PM.

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    Re: Two ways to do the same thing.

    To Colin's formula a non HDR with underexposed highlights to reduce CA stacked in Helicon Filter (I didn't know you could do that) sharpened with Topaz and generally messed around to make it look as bright as it was, But NO noise reduction so as to keep what little detail there is in lowlights; is it any good?

    Two ways to do the same thing.

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    Re: Two ways to do the same thing.

    You mention that "But NO noise reduction so as to keep what little detail there is in lowlights"...there is a way to reduce chroma noise in lowlights, and I think that you'll recognise it - change the image mode to LAB, select the shadows using the Magic wand on the darker bits of the Lightness channel. Then applying Gaussian Blur to the A&B channels - experiment here! I tend not to touch the lightness channel itself for N/R, as it's the chroma which I dislike.

    HTH

    Peter

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    Re: Two ways to do the same thing.

    Actually I think I made a mistake; where I said no noise reduction I do use a noise reduction brush to smooth clouds,and I did here but that is all. The LAB sounds clever but I haven't got it. However I can selectively remove chroma with Topaz DeNoise, this is a bit experimental down to not even straightening because it is only about 1 pixel out and I don't want to introduce rounding errors.

    Since highlights are 1 stop underexposed and only a small amount of memory although I can't remember how much, is used to store lowlights I thought it best to avoid destructive noise reducing techniques but chroma should be ok.
    Cheers anyway

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    Re: Two ways to do the same thing.

    Quote Originally Posted by arith View Post
    is it any good?
    More to the point, what do you think? (looks fine to me!)

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    Re: Two ways to do the same thing.

    Quote Originally Posted by arith View Post
    To Colin's formula a non HDR with underexposed highlights to reduce CA stacked in Helicon Filter (I didn't know you could do that) sharpened with Topaz and generally messed around to make it look as bright as it was, But NO noise reduction so as to keep what little detail there is in lowlights; is it any good?

    Two ways to do the same thing.
    To me there appears to be little GREEN CAST. In PS - select colour balance, highlight, and megenta /green make it " -12 and green cast will be removed

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    Re: Two ways to do the same thing.

    I think it looks fine Colin; just need 9 instead of 3 images with the top one 1/9 opacity, then things would be very close to good. The chroma I can do easily without loss of detail.

    An extreme cleaned up and cheating because I've reduced chroma noise with topaz, but I will try something similar again with more images.
    Two ways to do the same thing.

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    Re: Two ways to do the same thing.

    Cheers Ashwin, I think I deliberately put it in to make the grass look nicer but I can put it back again.

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