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Old 02-09-2009, 08:29 PM
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Quark (Trevor)
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Advice on using Masks in CS4

Hi All,

I have Photo Shop CS4 and need some help in using the Mask feature.

When imaging Jupiter, if a moon is present, over the time that it takes to capture the R, G & B channels, the moon gets slightly displaced from channel to channel.

I have merged the same RGB channels to produce 2 images, 1 image aligned with features on the planet and 1 image with the moon as the alignment feature.

I would like to be able to place a mask of the aligned moon channels over the misaligned moon in the other image.

I have attempted this as follows;

In CS4
Layer > New > Layer via Copy
Then used the rectangular Marquee tool around the aligned moon and dragged it onto the other image.

Not sure if that is correct or not, after doing this I can still pick the outline of the new layer, how do I deal with that outline or is there a better way of doing this.

Thanks in advance for any advice.

Regards
Trevor
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Old 02-09-2009, 09:01 PM
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sheeny (Al)
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G'Day Trevor,

Not that I've done any LRGB imaging myself, but I've played with Layers and masking a bit.

It may just be that PS only allows you to move the layer by a whole pixel at a time.

Try resizing your image up by say 4x prior to aligning the layers. Once aligned resize the image back to original size. That will give you at least 1/4 pixel alignment accuracy.

Al.
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Old 02-09-2009, 11:14 PM
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kinetic (Steve)
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Trev,

it may help, it may not but I vaguely recall either Paul H , Mike or
Bird mention exactly that problem in a thread recently.

Maybe try a few key search words.

I'm sure it was something about moons being blurred when registering
on the planet , and Jup features being blurred when registering on
a moon limb/ feature....

Hope this helps...

Steve
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Old 03-09-2009, 04:42 AM
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iceman (Mike)
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Here's how I do it:

On your "Moon aligned" image, change the selection type from square to circle, and set a feather of 2 pixels.

Select an area a few pixels larger than the moon, and ctrl-C (copy).

Then just paste that selection over your "feature-aligned" image. It will be pasted as a new layer.

Then just use the move tool to move it in place over the moon. I just use the arrow keys, and use the "eye icon" to "blink" the layer on and off to be sure you've aligned the "aligned-moon selection" correctly over the old-moon.

It's the feather that will ensure you don't get hard lines or edges when it's pasted over the top.

Let me know if you get stuck and i'll post some screenshots.
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Old 03-09-2009, 11:56 AM
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Quark (Trevor)
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Quote:
Originally Posted by sheeny View Post
G'Day Trevor,

Not that I've done any LRGB imaging myself, but I've played with Layers and masking a bit.

It may just be that PS only allows you to move the layer by a whole pixel at a time.

Try resizing your image up by say 4x prior to aligning the layers. Once aligned resize the image back to original size. That will give you at least 1/4 pixel alignment accuracy.

Al.
Thanks Al appreciate the advice.

Quote:
Originally Posted by kinetic View Post
Trev,

it may help, it may not but I vaguely recall either Paul H , Mike or
Bird mention exactly that problem in a thread recently.

Maybe try a few key search words.

I'm sure it was something about moons being blurred when registering
on the planet , and Jup features being blurred when registering on
a moon limb/ feature....

Hope this helps...

Steve
Thanks Steve, Mike has just posted how he does it.

Quote:
Originally Posted by iceman View Post
Here's how I do it:

On your "Moon aligned" image, change the selection type from square to circle, and set a feather of 2 pixels.

Select an area a few pixels larger than the moon, and ctrl-C (copy).

Then just paste that selection over your "feature-aligned" image. It will be pasted as a new layer.

Then just use the move tool to move it in place over the moon. I just use the arrow keys, and use the "eye icon" to "blink" the layer on and off to be sure you've aligned the "aligned-moon selection" correctly over the old-moon.

It's the feather that will ensure you don't get hard lines or edges when it's pasted over the top.

Let me know if you get stuck and i'll post some screenshots.
Thanks very much Mike I appreciate the instructions and will have a go this evening.
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Old 03-09-2009, 08:39 PM
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Quark (Trevor)
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Quote:
Originally Posted by iceman View Post
Here's how I do it:

On your "Moon aligned" image, change the selection type from square to circle, and set a feather of 2 pixels.

Select an area a few pixels larger than the moon, and ctrl-C (copy).

Then just paste that selection over your "feature-aligned" image. It will be pasted as a new layer.

Then just use the move tool to move it in place over the moon. I just use the arrow keys, and use the "eye icon" to "blink" the layer on and off to be sure you've aligned the "aligned-moon selection" correctly over the old-moon.

It's the feather that will ensure you don't get hard lines or edges when it's pasted over the top.

Let me know if you get stuck and i'll post some screenshots.
Mike, have just successfully followed your instructions and got a great result, this is something I should have learned to do a long time ago.
Love the way the copied section disappears by clicking on the eye icon and just how accurately the copy can be placed using the arrows.

Have attached some examples from Aug 31st with Io and its shadow aligned.

Thanks again for your help, I really do appreciate it.

Regards
Trevor
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Click for full-size image (j2009-08-31_12-55_rgb_tbaA.jpg)
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