Photoshop (and other image processing) Tips.

[Tandum]

Wouldn't it be nice if there was a section on Photoshop Tips. It appears to be the tool of choice. I have no idea on how to keep the chit chat out but things like : holding down the ALT key when moving the white point in levels shows clipping in the colour that you are clipping with the movement : are not common knowledge and are not documented.

[iceman]

That is a nice tip!
More and more tips can be added and then converted into an article (minus the chit chat).

[Ric]

A good idea Tandum, even though I use Paintshop Pro I find a lot of these tips and ideas can be easily converted for use.

Cheers

[dugnsuz]

Great idea.
Mike, tie jase down to a chair and apply the thumbscrews to get every last bit of processing know-how out of the man!!:P

[jase]

:lol: Not the medieval torture...

Here is a couple to make a start (basic ones first).

Double clicking the grey background in PS is a quick way of bringing up the open file dialog box.

Use spacebar to activate the "grabber" to move around the image (everyone knows that surely)

When using masks (either hide - black mask or reveal all white mask), use the X key to switch the white/black palette. If you've used a colour select function and the white/black palette has changed, use the D key to change it back to the default.

Talking masks. If you want a closer look at your mask, present the Alt key while you click on the mask in the layers panel. It will open and allow you to make finer adjustments.

When working with selections, use the Control+H key to hide the selection edge/lines. Push it again to bring it back. This is great when selecting stars to work on as the selection can sometime be distracting. Just remember that you've still got the selection active.... it is still active even if its hidden. I think its Control+D to deselect.

On the topic of selection - star selection (an alternate way to using the colour range tool)

Make a grayscale copy of the image. I'll call this image #2.
High-pass filter image #2 with a radius of one pixel.
Apply a Gaussian blur to image #2 with a radius of one pixel.
Invoke Image->Adjust->Threshold.
Adjust the Threshold Level one click at a time until just the stars are white and everything else is black.
In the original image, in the Channels Palette, create a new channel. Name it "Stars." Choose "color indicates masked areas."
Paste image #2 into this channel.
Make just the RGB channels visible (i.e. make the Stars channel invisible).
Discard image #2.
In the original image, invoke Select->Load Selection. Choose the Stars channel you just created.
Invoke Select->Expand and expand the selection by a few pixels (e.g., three). Done. I'm not sure of the source of this, I think it could have been Russ Croman.

Tip...of the iceberg perhaps, but its a start.

[iceman]

Nice work! I hope others continue to contribute tips here.

To make sub-pixel alignments when aligning your RGB channels, increase the image size by 400%, giving you 1/4 pixel alignment ability. When it's aligned to your satisfaction, reduce the image to 25% (back to original size).

[sheeny]

Here's another one I'm sure everyone knows (well I know someone won't, that's the point of posting...)

When using the brush tool (even when masking - which is what I use it for most) use the [ key to reduce brush size, and use the ] key to increase brush size.

[mdgodf]

Pick up one of Scott Kelby's books...or visit his web site at http://www.scottkelby.com/ for lots of photoshop tips.

[jase]

ok, here are a few others I use. Geez I feel like I'm coming clean on some of the tricks.:lol:

Capslock key will change your pointer into accuracy mode (target cross hairs). Great for highlight masks and other features. Push it again to change it back.

When you are working with layers that aren't aligned and you want to align them, press and hold the control key... it will change the current too into the move too until released.

Control +/- will resize the image. Control 0 or any other key will active fit to screen function

Control+J duplicates the currently selected layer.

When using the a select tool - say the elliptical marquee tool, hold down the space bar to move the selection around. This makes it easier to frame aspects of the image i.e. a halo/reflection of a star you wish to remove.

A request for a CS2/CS3 user... can you create an adjustment layer on a layer mask (say reveal all mask for instance)?

[leon]

Gees guys I'm lost already. :lol::lol:

Leon :thumbsup:

[Bassnut]

Top idea, a single no chat source of PS tips. Like Jase, ive picked up so many crackers over a long period of time (not that it did me any good ) . To be able to see tricks in one place them without stumbling over them by accident over a lifetime would make a nifty seperate catagory.

[iceman]

For sure. Once we've got a sufficient supply of tips in here i'll put them into an article that will be added to over time.

It would be perfect for the Wiki idea, in the future ;)

[Bassnut]

No Mike, please not a Wiki format, that sucks :mad2:.

[dugnsuz]

Make this a Sticky Mike???

[Glenn Dawes]

Hi guys,
I think a photoshop tip thread is a great idea! So here's my 2c worth. Some may think it is basic but I'm hoping someone might appreciate it. Many of the lunar images in the yearbook, over the years, have been done this way.

Regards

Glenn

CREATING MOSAICS IN PHOTOSHOP

1 Open the first image and expand the canvas to a size to cover the whole Mosaic
IMAGE > CANVAS SIZE. Move the image to its correct position (drag the square) before resizing (width and Height)

2. Open second image SELECT > ALL

3. SELECT > MODIFY (specify border between 5 – 10 pixels)

4. SELECT > FEATHER (enter same number of pixels as 3. above)

5. SELECT > INVERSE

6. EDIT > CUT

7. Close window and EDIT > PASTE into your first image you resized. A new layer will be automatically created on top of the original.

8. LAYER > LAYER OPTIONS. set opacity level to 50%.

9. Merge images to your satisfaction using the “Move Tool” and if necessary Rotate using LAYER > TRANSFORM > ROTATE.Then set opacity back to 100%

10. Repeat steps 2 to 9 for remaining images

11. Using IMAGE > ADJUST > CONTRAST/BRIGHTNESS or CURVES Match the appearance of the layers (remember to “click” the layer you wish to adjust).

12. Save document as a Photoshop document (to allow you to return to it if necessary)

13. Flatten Image LAYER > FLATTEN IMAGE. You can no longer modify individual layers, however you can now crop (using IMAGE > CROP) and process image (eg. IMAGE > ADJUST > Contrast/Brightness) as a whole and saved in whatever format you need ie. FILE > SAVE AS (then Tif).

[xstream]

Done!

[Garyh]

Boy I like this thread!
I`m learning a few new tricks here!
cheers Gary

[dugnsuz]

Thanks a lot - this is going to be a great resource.
Now, no more chit chat from me!!:lol:

[jase]

Alternate method to performing HaR combinations - courtesy Don Goldman:

Create RGB and Ha Tiff files in Camera control software of choice i.e MaximDL, CCDSoft etc.
Process both in PS CS until about 80% finished
Split channels in the RGB
Layer Ha over R channel with normal mode and 30% opacity
Use HaR as red channel and combine RGB
Finish RGB processing
Finish Ha as Luminance
Saturate RGB by 30%
Paste in Luminance (Ha) using luminosity mode
Duplicate the RGB and use as top layer in soft light mode with 20% opacity

The above works quite well.

Noise invert mask "NIM" - courtesy ME :D

When close to the final steps of processing duplicate the flattened image
Create a layer mask on the duplicated image (reveal all)
Copy the original image
Click on the mask while holding the Alt key to fit the mask to screen
Paste the original image into the mask (it will turn grey - which is normal for masks)
Inverse the masked image ( the background turns white, while features grey or black)
Use levels on the mask to increase/decrease the mask size/impact.
Select the layer that has the mask applied
Apply a moderate to heavy noise reduction of your choice (X blur, dust&scratches, neat image, whatever)
If its too heavy, drop the opacity from 100% and/or duplicate the original layer again and use lighten mode to bring some stars back (if required).
NOTE: With the inverted mask anything that is black is not pushed through the noise reduction function. Use the levels slider wisely. You can also paint the mask to ensure certain areas i.e. details, stars, blah blah are masked as needed.
Flatten and enjoy. You don't have to wait until the end of the routine for this. It can be applied if you've got plenty of layers. Choice is yours.

That will be all for now. May provide more later.

[Tandum]

Highlight Mask or Brighten DSO. This lets you brighten up a DSO without effecting the sky and stars.

Press Control-J. (Layer via Copy).

Select all of the original image and copy to clipboard.

Layer > Layer Mask > Reveal All. (Create a layer mask).

Alt Click on the new layer mask icon in the layers palette and paste, then invert that layer. Image Adjustments > Invert.

Increase the contrast of that mask with levels or curves. Move the black point to about 64 and the white point to about 220. Experiment with these points.

Apply a small gaussian blur to the mask.

Select the original image and drag the white point to the left in levels to brighten the DSO.

The opacity of the layer may also be adjusted.

Flatten the image when done.

[Tandum]

Unsharpen Mask.

Just tried this one tonight for the first time and it worked a treat. Good for bringing up nebula detail. Can take a bit of fiddling to get the desired result.

Make a duplicate of the original image. (Select all > Copy. File New > Paste.)

Blur the copy to remove stars or clone stamp if they won't blur. You don't want any stars left in the copy and you don't want a totally blurred blob as an image. (Filter > Blur > Gaussian Blur)

Reduce the brightness and contrast of the duplicate to about -30. (Image > Adjustments > Brightness and Contrast.)

Subtract the duplicate from the original. (Image > Apply Image. Scale=1 Offset=0)

Adjust the white point in levels of the resulting image as it will be dark.

The end result changes with the blur amount as well as the Brightness and Contrast settings on the copy. In CS3 click on the original and do a Window > Arrange > New Window and it should show you a preview image. :P

[TrevorW]

Latest copy of Australian Sky and Telescope has an article on PS layers etc quite helpful

[gregbradley]

Hi,

I tried this but perhaps I did the wrong thing near the end when you say select the original image. To do this you click on the background image in the layers box? Or do you alt click on the original image in the layer 1 box?

When I moved the white point doing the first above it made everything brighter the same as if I just opened the image and moved the white point to the left.

Greg.

[Tandum]

Yes, you click on the background and move the white point. Did you paste from the clipboard to the layer? The layer will be a black and white image and should look like a negative of the original image once inverted. When adjusting levels on the inverted image, the dark bits are the bits that will be acted on when moving white point or adjusting curves on the background. So the sky should be white and the object of interest should be darkish. The amount of blur will also effect the result. It's just a mask really so you can use it to colour mix etc etc as well. I tend to be just lassooing the objects lately to mess with them, but I'm just being lazy :)
robin

[jase]

RE-selections
Control + D can be used to deselect an area or selection criteria. However something pretty cool is the the reselect feature - Control + Shift + D. PS will only remember the last selection criteria.

Drag Selections (oops - just realised I've already mentioned this in post #9)
This works really well if you want to chase filter reflections or star halos for what ever reason. Use the selection tool of choice, typically the Elliptical Marquee Tool (hot key - Shift + M twice), select the halo or reflection, before releasing the left mouse button, hold down the spacebar to move the selection around - release the spacebar to resize the selection if desired. This will allow you to precisely select the reflection/halo and unselect the star to form a "donut" selection to ensure specific processing does not alter the stellar profile.

Zoomie Zoom
Control + Alt + mouse scroll wheel up or down to zoom in or out respectively. Also, double clicking the magnifying glass (zoom) button in the tools palette is a quick way of zooming to 100% (1:1).

Brush size and hardness
Mentioned in a previous post, the [ ] (square bracket) keys alter the brush size...an extension to this is the hardness of the brush. This can be altered by pushing Shift + [ or ] to alter on the fly. I don't alter hardness often, but it is useful.

Supafast layer opacity adjustments
This is not really a tip, but I use it all the time as its a time saver compared to fluffing around with the mouse. Select the layer you want to change the opacity on, say a rich Ha data set that when blended at 100% is too rich for the RGB data. Simply use the numerical key pad to enter the opacity value. 1 = 10%...9 = 90%. If you type specific numbers in quick succession, say press 4 then 5, the opacity will be 45%. Too logical huh?

Tool-less view
If you're working on a system with a restricted desktop resolution and you find you're for ever scrolling about and shift tool palettes to get a better view of the image you're working on, simply hit the TAB key to hide them, hit it again to bring them back. This is a cheaper option than setting up a dual display graphics station where you have one monitor for the image and the other for your tools.

OK, here's one from my friend the Pixel Princess (had better give credit where its due as this is cool, well I think so as I've used it a few times).

Visible layers into a single new layer (w/out flattening of other layers)
In the layers, select the layers you'd like visible i.e. have the "eye" beside them. For example, an Luminance and RGB data set. Then press Control + Alt + Shift + E. This will merge the visible layers into a new layer while still leaving the original layers intact. You can then go on to use a hard stretch, saturation pump up activated as softlight blend for a LRGB colour boost.

Enjoy!

[jase]

Colour dodging is an alternate method to boost colour saturation.

Here are the basic PS steps. You can add to the routine as you see fit.



Duplicate the RGB layer twice, so you have three layers.



On the top layer, set the blend mode as “colour dodge” and leave the second layer as a “normal” blend.



Uncheck the original layer (select the eye icon) so it’s no longer visible, then go to Menu | Layer | Merge Visible. This will obviously merge only the visible layers (the top two layers).



Now you’ve got two layers, the top one will look heavily saturated. Set this as “colour” blend and recheck the eye on the original layer (bottom layer). You can alter the opacity of the colour blend layer to taste (50% is a good start) – be careful you don’t wash out the star colours. I usually apply a hide-all mask to the layer to selectively apply the colour enhancement, but the choice is yours.

[ColHut]

Gosh thanks all Unfortunately Ii use JASC paintshoppro 9.11. The ideas are great though - just need the keys!

[jase]

The technique defined below can be used to address colour related issues due to stars that are off the edge of frame. These stars, if bright enough, often cause colour flares that detract from the images appearance. The technique can also be used to address other colour related issues. In summary the concept is to copy a "good" piece of the sky that has contains the desired colour hue over the top of the offending colour flare. A follow up step brings the stars of the repaired area back to their original form.


Click on the lasso tool and set the feathering to approx 20 pixels
Using the lasso tool, select an area that is of same size and is relatively close to the colour flare area you wish to remove. The purpose of this exercise is to match the background hue of the surrounding area so the proximity to the area you're trying to fix is fairly important. At this point, don't worry if the selected area contains stars.
Copy and paste the lasso area so you now have a new layer that contains the small patch of the sky in which you've just copied.
Hold down the control key and move the mouse to shift the small patch over the colour flare area you wish to remove.
Now go to the Filters | Noise | Median
Increase the radius until you see no more stars in the small patch of sky that you've copied. If you don't like the median tool, dust and scratches, or the minimum filters can do a similar job. Median I've found works well in general.
With the patch layer selected, change its blend mode from normal to colour
You'll now notice that your colour flare has disappeared i.e. has been blending into the surrounding background hues. If it hasn't you may need to increase your selection size or reduce the feather.

...but don't stop there...look what you've done to the stars in the area that's been repaired...they've inherited the same background tone you copied. Easily fixed...


Select the original layer and use the colour range tool to highlight the stars. Alter the fuzziness slider until you get a good match.
Expand the selection by 2 or 3 pixels (or to your taste)
Feather by 2 pixels (or to your taste)
Then select the patch layer (important, make sure its selected!!)
Hit the delete key
POW! You've now brought the star colours back in the repaired area...as you've deleted the selections from the patch layer so the colours come back through from the original layer.
If you find that the colour range tool selection wasn't ideal, you can always use the eraser tool to do a similar task, but I would recommend going back a few steps until you get the right selection i.e. manipulate fuzziness.

Enjoy!

[luigi]

Sometimes I like to use the asinh command of IRIS to stretch colors, it can be either very good or very destructive.
I try asinh 0.005 30 as a way to start

[Octane]

asinh is the bomb.

H

[troypiggo]

If you're using it with PS, at what stage do you use IRIS? Beginning, middle, or end?

[luigi]

In my case before PS.

[luigi]

If you have some other bombs to share I'm all eyes :thanx:

[Tandum]

Can anyone fill me in on how to remove stars from an image?

[troypiggo]

Think there's a tutorial here: http://astroanarchy.blogspot.com/2009/04/neaic.html and he also has a PS action you can download to do it for you.

[Tandum]

Cheers Troy, I'll check it out.

[Bolts_Tweed]

Gday

Still waiting for the presentations from AIC but heres one I remember from Tony Hallas that I wasnt aware of (not saying much).

Usually using the saturation slider in Hue and Saturation introduce noise into the image (I knew that bit) - Hallas suggested this.

Change the mode of the image to lab colour. You will then have 3 channels Luminosity, A and B. Dont touch luminosity. Channel A contains the reds and yellows (from memory) and Channel B the Blue and Greens. Add a curves layer on top of the background layer (clip it if you are doing anything else) and adjust the curves for the required layer. eg if you want to increase reds select the A channel from the pull down menu and lift the centre of the curve (actually you can do whatever adjustments to the curve you like. lifting the curve will boost the red - lowering the curve will desaturate these colours.

Season the colour satruation to taste and then flatten the image. You can then save it back into RGB mode. You have then adjusted the saturation without the introduction of any noise (provided you didnt touch the luminosity channel). Obviously it can be done on masked sections, lassooed sections etc of the image etc etc like any normal processing.

Works well

Mark Bolton

[Octane]

Mark,

That method screws up the histogram once you convert back to RGB.

If your histogram is unclipped prior to LAB conversion, watch what happens to it after converting back to RGB -- especially if more work is still required post-conversion.

Seems LAB colour mode comes in and out of fashion every now and then. The trick to it is to use it sparingly as it is very, very easy, to overdo it!

H

[Bolts_Tweed]

Thx H

As i said i havent tried it (still on hols - no data)

M

[jase]

Rediscovered this document which I developed as a basis for a planned presentation which fell through. It was produced back in 2007 and seen a few updates but overall is incomplete so take it with a pinch of salt.

Despite this, I thought I'd share it as its benefiting no one sitting on my hard drive, plus I have no inclination to complete. I take no responsibility for errors or the 'stuffing up' of data sets if you follow these principles, though I still use the analysis techniques today.

Enjoy!

[gregbradley]

I posted this on another site but it became quite detailed so I thought it may be helpful to others.

It assumes you use CCDstack and Photoshop and use CCDsoft or Maxim DL for controlling the camera and taking the actual images.

It is based on using processing techniques written up in Ron Wodaski's book The Zone System and it is also based on DVD tutorials by Adam Block (one of the best) and Tony Hallas (also very good).

If you find it confusing or want something clarified feel free to PM me for clarification:

Image acquisition. Save to a file named after object. Make sure the filter wheel is labelled correctly so red is red and not blue etc.
Image LRGB with luminance say 2 hours of 10 minutes subs 1x1 and RGB 10 minutes 2x2 and 30minutes each minimum.

CCDstack
open all the luminance
dark subtraction and flat fielding
normalise using a bright and dim area in one selection box in the image.
data reject hot/cold pixel removal
register (I use the CCDis alignment plugin - its worth the $99)
combine - median.
save in file above with a new file called masters. Call it master luminance (number of subs)
I then run a 40 iteration deconvolution on luminance usually unless its a nebula.
save that.

Open all reds.
Do the same as above but usually I don't do deconvolution on RGB unless one is a bit bloated like blue.
Save each as an Red, green and blue master.

Open master deconvolved luminance and the masters for each of RGB.
Using luminance as base register (if you took Ha you do that now as well so they are all registered).
Save them all replacing the original masters - now all masters are aligned.
Create colour and create an LRGB at this point. Some may only make an RGB colour here. I use LRGB here. Sometimes I need to normalise RGB only if I get weird colours.
I select desaturate background as its often bright red or blue or something weird.
Save colour image as a tiff (all above saved as 32 bit floating tiff files).

Open the LRGB and luminance in Photoshop.
I work on the luminance with levels and curves.
then often a duplicate layer set to soft light and opacity to suit to increase contrast.
Often high pass filtering to increase sharpness and detail.
correct any gradients first up using Gradient Xterminator or gradient methods as in Adams tutortials.
Save luminance.

Do the same for the LRGB but you are more working on the colour, saturation, the stars, the star sizes, the areas of interest selected out and tweaked etc.
Now add a new layer and add the processed luminance this gives LLRGB really and you will see it make the image more luminescent.

Do final tweaks using masks usually for noise control (near the end of the processing) and final enhancement of details and colour.
Save final image. I save each version with V1 V2 suffix so I can revert to an earlier image if things go wrong.
I do a clean up of any background artifacts using the healing tool (there are often a few odd coloured pixels that get through or satellite trails etc).
I reduce the final image to 8 bits, 1200 x 1200 or thereabouts and save as a jpeg maximum settings for posting on the net.

You need to know how to do inverted masks, layer masks and levels and curves and know the basic tools of Photoshop and how they work.

That's it - piece of cake!! phew!

Greg Bradey

[DavidTrap]

So can you tell me how to do it in PixInsight and how to use all the tools in clear easy to understand language?

;)

I'll try to digest what you've written later!

DT

[cventer]

Greg,

Good post.

Be great to have this worflow for OSC Cameras as well. Many beginners use OSC be it QHY or DSLR

Also a workflow using the typical free or cheaper tools like DSS and Nebulosity would be awesome.

[gregbradley]

I am a beginner when it comes to Pix Insight. So I can't help you there. I intend to learn it soon though.




I have done OSC and DSLR. I used Images Plus which is popular but does cost around US$200 or so.

Here's what I did for that:

1. Create a dark library for one shot colour cameras that are cooled. Pick a couple not 10. Make a standard exposure length and a temperature you can achieve almost all year round or 2 temperatures - one for summer and one for the rest of the year. Shoot darks by simply setting the controlling software to dark and shoot it at night or in a darkened room with the lens cap on or at night.

You can do this with a DSLR as well. Its a bit trickier with DSLRs because they are at air temperatures and of course that varies not only throughout the year but throughout the evening. They will be less noisy on cold winter nights and most noisy in summer.

It is also best to shoot darks with a DSLR and use a DSLR with the power adapter rather than using batteries if you can. Batteries heat up with use and change the noise of the camera. The power adapter does not.

With DSLRs you also need to standardise your ISO as well as the exposure length.

ISO of 400 or 800 is usual. Above that you are only amplifying what is already there so much like boosting it afterwards with software. You didn't really gain anything except stretch what was already there.

DSLRs in light polluted areas will pick up sky glow faster than dedicated astro cameras so work out an ideal exposure length for your area.

3-4 minutes at ISO800 may be close to ideal in a typical urban setting.
You may also need a light pollution filter. Survey shows Hutech LPS-2 or IDAS are the ones to use.

So take about 12 darks or more. Why so many? Because there are random artifacts that the combining process removes so the more the merrier in that regard.

use sigma reject combine for making master darks out of the 12 you took.

Now take a flat field. Put a white t-shirt over the end of your scope and make sure there are no wrinkles. You may need a large elastic band to keep it taut.

At dusk point your scope to a clear area of the dusk sky and take an exposure to about 1/3rd your DSLR histogram and very short exposure.
For one shot colour that is around 20,000ADU. Take about 6.

With flats make sure your scope is in focus and the camera is in the same orientation that you will or did take your images at. If you change that they will not be valid.

Also make sure if you are using a one shot colour camera that is cooled that the camera is cooled to the temperature you will be imaging at.

Also make sure you take fresh flats if you clean your camera window or filters as flats remove the effects of dust shadows in your images.

Take some flat darks (3 to 6) meaning take a dark image of the same duration as your flat exposure.

Now use your astro software to create master darks and master flats.
Images Plus does that. Use median combine and subtract the master flat dark from the flats to make the master flat.

Ok so now you have flats and darks for your camera.

2. Take your exposures with exposures planned as above (exposure time is determined by light pollution, type of camera - DSLR shorter, one shot colour longer so DSLR maybe 3 minutes and one shot colour may be 10 to 15 minutes. Take lots like several hours. Have patience, good images need long exposures - like 3-20 hours worth. Its better to stay on one object for several nights than take 10 short images of several objects none of which will turn out that great (easy to say hard to do).

3. Now you have your images, your matching darks and your flats.

So you callibrate the images. That means removing the dark noise, correcting the vignetting (shadowing in the corners) and the dust shadows (called dust donuts) and uneven illumination of your scope and camera with flats.

With DSLRs and one shot colour for that matter, you can use adaptive darks. This means as long as the dark image is accompanied by using a bias (very short exposure of the read noise at the same temp as imaging, say 6 shots sigma reject combined) then the darks can be applied via software to different temperatures and exposures. This is handy if you did say a 5 minute exposure and only have 10 minute darks.
It is also handy for DSLRs that do not have temperature regulation for their sensors.

4. Now you have subtracted the dark noise and corrected the dust and uneven illumination with your flats.

Your image is probably pretty dull and hard to see. The image needs to be stretched/boosted to be able to see it. In Photoshop that is the levels/curves tool. In Images Plus it is the DDP tool.

Boost the image so you can see the image but do not clip the data. Clipping means to cut off some of the data - usually it is done when trying to make the background dark and you cut off some of the faint background data with it so watch the histogram and make sure the
histogram forms a nice bell curve and you do not see it hard against the left with part of it being a vertical wall on the hard left.

Next step is to align the images. The images are aligned. Images Plus has some great alignment tools for that. Try out a few and see which ones you like best.

Some split the image into luminance and red green and blue here. They do that so they can process the luminance separately and differently to the rgb. RGB is usually processed to enhance colours, adjust colour balance to get rid of a colour bias. Luminance has all the details so it is usually sharpened, increase the contrast etc.
You recombine these at the end. I am not sure if you need Photoshop to do that with its layers ability or if you can do that in Images Plus (you probably can).

You don't have to do that step and it depends on the image. In an image
where you want maximum details you'd do it (like a galaxy or detailed nebula) but on a diffuse nebula it won't gain anything so its not worth doing.

This is a basic overview to help you get started. Ron Wodaski's books are good and Images Plus is the king software for one shot colour or for DSLRs and there is an excellent group that offers advice and tips for it.

I hope this helps.

Greg.

[jase]

I originally produced this for Lightbuckets members who were just starting out with RGB filtered imaging. I thought I'd post it here as well given I didn't want such information to go into a blackhole, never to be seen again.

Other the overall work flow (which is a couple of years old now I should add), the focus of attention was on normalising of data. This is a very important step in a workflow, but I found the term is often used loosely, hence there can be confusion as to the definition. Normalisation is a processing activity that equalises data for two purposes. These are;

Normalisation for data rejection
Normalisation for colour combine

Normalising for data rejection typically occurs after you have registered the subs and hot/dead pixels have been removed. The act of normalising the data to the same level (equalisation) across the sub frame set is vital in determining what data is considered outlier i.e. what data does not conform and should be considered noise or another form of erroneous data and be rejected. If the sub frames are not equalised prior to the data being combined, the data rejection algorithm will fail to determine what is "correct" or normal value of specific pixel. Depending on the tool you use, normalisation is automatic. In MaximDL there is a small check box in the combine dialog box asking if you want to normalise the subs before combining the data. In CCDStack, the normalisation process is more of a manual task were you have the opportunity to select in the image data what constitutes as being a highlight (bright area) and background (dark area). Once normalised, the average values of the pixels amongst the subs should be relatively close to each other.

Normalisation for colour combine is performed on the R, G, B master frames. That is the sub frames per colour channel that have already been combined to produce a noise free master frame. The act of normalising the R, G, B master frames is to equalise the background colour between the frames so that the correct colour weights are applied. For example, you may have blue filtered data that was collected when the moon was rising, as such the background is brighter then the R and G filtered data. Without normalisation of the background, the resulting colour combined image would have a strong blue cast across the image. Normalisation simply alters the pixel values across the three filters master frames (R,G,B) to similar values (again equalises).

The attached processing 101 flow chart highlights where normalisation is performed. The first set is the data rejection i.e. prior or during the combine algorithm executing. Then, the colour combine normalisation that occurs only on the RGB master frames.

The work flow listed is dated though is proven to work having produced several images using the flow in the past. Of course should you have any questions, please PM me or establish a new thread for discussion.

Cheers

[solissydney]

Which version Photoshop are you referring to? All of them?
I use photoshop 7

[sanusense]

it will be easier if you are using photoshop 7, very user friendly.

[salimant]

thanks jase