Combining multiple exposures

[greg_hillje1]

<p>Question: I took a series of about 100 shots of windmills using a tripod. I want to composite them all together to create the appearance of a long exposure so the windmill blades look blurred. What method can I use in Photoshop (CS5) to accomplish this? </p>

<p>-Greg</p>

<p> </p>

[Mattman944]

<p>For a few layers, this is the general procedure to average layers, see the layer formula near the bottom:<br>

<a href="http://www.cambridgeincolour.com/tutorials/image-averaging-noise.htm">http://www.cambridgeincolour.com/tutorials/image-averaging-noise.htm</a><br>

For 100, it isn't really practical. But, you could average 10 at a time, then average those 10 into one.</p>

<p>Astrophotographers regularly average (stack) large quantities of images, so there are other tools out there that might work for you. These tools also align the images, so the moving part of your images might confuse the tools.</p>

[robert lee]

<p>Use <a href="http://enblend.sourceforge.net/">enblend</a>.</p>

[greg_hillje1]

<p>Matthew, I don't think that method would work for this purpose, since it relies on opacity, and I'd like to get the maximum opacity of the windmill blades from each exposure. Essentially, what I'm hoping to be able to do is use stacks and set the blend mode, but it seems the only ones that get close to what I want to do, do the OPPOSITE, ie mean or median.<br>

Robert, I haven't tried enblend yet, it looks possibly promising. It's command line only? </p>

[greg_hillje1]

<p>Actually Robert, you may have misunderstood. Enblend looks like a panorama stitching tool, which is not my goal here.</p>

[tom_mann1]

<p>Greg, as you probably know, "median" is not going to work. It finds the most likely value of a given coordinate among all images in the stack. Its typical use is to remove tourists from photos of busy monuments, ie, the moving things (the tourists) are removed, the stationary things (the monument) is retained. You kinda want to do opposite, but not quite in that it while it would be OK for you to treat the stationary parts of the scene with something like a median filter, OTOH, you have to treat the moving parts differently and retain them, although in a blurred way.</p>

<p>If the windmill blades are darker than the background sky, a stack of layers, each with the "darken" blending mode will maximize the opacity wherever there's a chance that a windmill blade might be there. However, I don't you will be happy with this result either if you are looking for a realistic spin blur. I would probably just take one exposure and then use the circumferential / spin mode of the radial blur filter in PS. </p>

<p>Since that filter only makes perfectly circular blurs, if you are not square to the windmill, you will have to do an affine transformation to square up the windmill before the blur, then apply the blur, then apply the inverse of the first transformation to ensure the direction of the blur is believable.</p>

<p>Tom M</p>

[tom_mann1]

<p>PS - Why didn't you just use a long exposure in the 1st place? Yes, if it's the daytime, an ND filter and low ISO would likely be necessary.</p>

<p>PPS - Why don't you post one of the images from this set.</p>

<p>Tom M</p>

[greg_hillje1]

<p>Tom, thanks for the response. Yes I'm aware that median is not what I'm looking for. I guess I wish there was a blending method that worked the opposite of that, you know like for instance instead of removing people from a shot, you do the opposite, and ADD people to a series of images to create a bigger crowd. Except in my case, it's blades on windmills. </p>

<p>I would have loved to do a long exposure in the first place, but being broad daylight, I would have needed far more ND filters than what I have. I attached one of the shots to give you an idea of what I'm dealing with.<br>

Thanks.<br>

Greg</p><div></div>

[roger_smith4]

<p>Emblend does work to combine multiple exposure (not just panorama.) I use Photomatix's blending feature but have no use for large numbers of exposures with my work (normally less than 4 shots.)</p>

[michael_b9]

<p>Hi Greg,<br>

I'm trying to do something similar to you and was wondering if you've managed to find a solution.<br>

I've taken a series of shots of a seedling growing, at 30min intervals over about a week. <br>

Whilst one of the things I wanted to do is stop motion video, I'd also like to produce a 'still' capturing a composite of them all. Just like stacking physical transparencies... which is of course another option...<br>

thanks in advance,<br>

m</p>

[tom_mann1]

<p>Greg - Sorry for the long delay, but was busy, then out of town. I'm curious: Did you ever go back and try the "darken" mode or any of the other suggestions?</p>

<p>HTH,</p>

<p>Tom M</p>