For those interested in imaging and image processing with DSLR, CCD, webcam or film.
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Post by cstone » Sun Jan 31, 2010 9:28 pm

I struggling to use IRIS so I was wondering if anyone can give any hints and tips. I understand there are some tutorials on the site but I cam getting stuck when it comes to making the darks and flats

Any help would be appreciated :D



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Re: Iris

Post by rwilkinson » Tue Feb 02, 2010 9:47 am

I found this step-by-step tutorial Diamonds from the Rough a very useful primer: ... _iris.html
or see our Members' Area.

But I reckon that for beginners, usable results can be achieved without using flats or darks, but using the camera's auto dark-frame routine instead. I'll make a "dummies' guide" as I go, to post here.

And once you've got to grips with this, you can proceed on to using the calibration frames, to get better results and halve your imaging time.

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Re: "Bluffer's Guide" to IRIS

Post by rwilkinson » Sat Feb 06, 2010 10:18 pm

Here as promised is the user-friendly guide to getting started with IRIS...

Ross’s “Bluffer’s Guide” to image-processing with IRIS

IRIS is a very comprehensive package (written by an astronomer who lives in a light-polluted city - not unlike Bolton - and has designed it to solve the problems we need to overcome), but it can be very daunting to the new user!
This is not intended to be a complete guide, just a first-time primer on the basics.
It’s assumed that you have a sequence of DSLR astro-images in RAW format, but no calibration frames (offsets, darks and flat-fields) are used: you can graduate on to those once you’ve mastered these steps!

Preparation (you only need to do this the first time)

1. Download and install IRIS from

2. In the File.. Settings menu, select your preferred working directory Working path and PIC file type (or you could use FIT if you wish use this common format with other astro-imaging programs)

3. Find the Camera settings menu (you need to click on the camera icon on the menu bar) and set for your Digital camera.

Loading your images

1. Open up a file explorer window and select all your RAW image files (Ctrl-click).
Then from the IRIS Digital photo menu, select Decode RAW files.
2. Drag and drop the files from the explorer window into the IRIS window (which has probably popped up underneath your explorer window!).
3. Choose a generic Name for the files (e.g. raw) and click on the >RGB button and then Done.
Note that loading a large number of megapixel files may take a long time!
4. You should eventually see the image raw1.pic appear – you may need to click on the Auto button in the Threshold window (or play with the sliders) and scroll around to see your subject!

Combining your image sequence

First we need to align all the images precisely, to take out any tracking errors from your mount. IRIS has a number of algorithms to do this: the simplest (and quickest!) is One star. This should work if you’ve used a motorised equatorial mount with reasonable polar alignment – otherwise you’ll have to use one of the other slower methods.

1. Find a single isolated star well away from the edge of the image and draw a rectangular box around it using the mouse.
2. From the Processing menu, select Stellar registration. Your Input generic name and Number should be pre-filled, but you’ll need to choose an Output generic name (I used ali – for “aligned”). Then select the One star Method and click OK.
Now you’ll need to wait for IRIS to step through each image in turn, locate your star and then calculate the shift required for alignment.
If it loses your star on some of the images, you’ll have to choose a different one and draw another rectangle – or bite the bullet and try One matching zone and go off and get yourself a cup of coffee!
3. When this is complete, you should have a set of registered images ali1.pic, ali2.pic… To combine these, from the Processing menu select Add a sequence, and make sure that you have Normalise if overflow ticked.
This bit is fun to watch, as you’ll see the composite image slowly building up on the screen, with the stars getting brighter as each sub-frame is added.
4. When this is complete, click on the Auto button in the Threshold window again, and press the zoom out icon in the toolbar to see the whole frame.
You’ll notice that your image is very green – this is due to the colour-weighting of the pixels in your camera, but you can correct this from Digital Photo.. RGB balance window: try 2.2, 1.0, 2.0 for the R, G, B coefficients (or if you took your pictures through a light-pollution filter, try 1.7, 1.0, 1.7)
5. Once you’ve done this, you should save this combined image before fiddling with it any further (so that you can come back to this stage when you make a mess of the next bit!). From the File menu, choose Save and put in a file name (I used step1.pic).

Processing your image

This is where things get much more subjective – don’t be afraid to experiment with the settings – you can always go back to your step1.pic image if things go wrong (File.. Load.. step1.pic).

1. As the image from your DSLR is thousands of pixels across, you’ll probably want to resize the image (this will speed up the following processing steps too). From the Geometry menu, select Resample and put in 0.25 for X and Y to get it down to a quarter of its original size.
2. Now you can try to remove some of the background light-pollution with the Processing.. Remove gradient (polynomial) algorithm: tick Balance background colour too. Then play with the sliders in the Threshold window when it’s finished.
By this stage, your image should be looking quite good, but there’s more fine-tuning to be done yet. But first, it’s probably wise to File.. Save it as step2.pic.
3. On the View menu, try some of the options Logarithmic, Modified Equalisation, Dynamic and Colour stretching, and play around with the sliders (and the ones in the Threshold window). If you don’t like the result, click on the Undo icon in the menu bar, or go back and Load step2.pic.
4. Once you’re happy with the result, use File.. Save to save the result as a .jpg file, or as a .bmp to import into your favourite photo-editing package (e.g. PhotoShop).

Improving your RAW images

Once you’ve mastered all these steps and got familiar with using IRIS, you should consider using Offset and Dark frames and Flat-fields and Cosmetic frames to get the best out of your camera: but that’s another subject…

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Re: Iris - calibration

Post by rwilkinson » Sat Mar 12, 2011 7:59 am

Further tips on the use of calibration frames:

Some of the detrimental effects of noise and other error signals may be removed by the use of calibration images, which should be taken under the same conditions as your star images.
And as with the star images, averaging a large number of frames will reduce the effects of random fluctuations (noise) between individual images – so take at least a dozen of each.

The offset (bias) image is formed from the average of a series of very short exposures with the lens-cap on.
IRIS will automatically generate the master offset frame from a series of images, from the Preprocessing..Make an offset menu. Then you should save the result, as you’ll need it in all the following steps: it will be automatically subtracted from every image.

The dark-frame is formed from the average of a series of exposures of similar duration as the star images, but with the lens-cap on. These should be taken at the same temperature as the star-images – you can do these whilst waiting for a patch of cloud to clear over.
Again, IRIS will automatically generate the master dark frame from a series of images, from the Preprocessing..Make a dark menu. Then you should save the result, as it will be automatically subtracted from every image.

The cosmetic list is then synthesized from the master dark-frame, and is just a map of the positions of your CCD’s hot pixels.
Once you’ve got your master dark, open the Command window and run the command find_hot coslist n, where n is a threshold setting which you need to choose: look at the number of pixels reported in the IRIS Output window, and alter this number to register between 100 and 200 pixels. IRIS will then remove the effects of these bad pixels from each of your images – otherwise they will leave a trail across your final stack (showing how your tracking had wandered during the course of the image sequence!)

When correctly applied, these three calibration files can remove a lot of the effects of thermal noise and CCD defects.
IRIS has a useful “optimization” function, which will optimise the weighting of the master dark to match your latest batch of raw images, which should remove the effects of temperature variation on your dark subtraction. To use this, you must first use the cursor to draw a small rectangle around a “dark” region (i.e. with no stars) of the first of your series of star images.

Finally, the flat-field is formed from the average of a series of exposures of a plain white card (or an empty patch of twilight sky). You must use exactly the same telescope (or lens) set-up (including focus and aperture settings and filter position) as with your star images – you’ll need to do a fresh flat-field whenever you change any of these.
When shooting the flat-fields, you need to use an exposure which will produce a mid-grey result, on which you can clearly see any blemishes from dust etc. - this is a particularly bad example:
flat.jpg (27.99 KiB) Viewed 16345 times
Again, IRIS will automatically generate the master flat from a series of images, from the Preprocessing..Make a flat-field menu. Then you should save the result, as every image will be automatically divided by this result.
When correctly applied, the flat-field can remove the effects uneven response of the CCD, vignetting in the optical path, and even the shadows of dust-specs on the optical surfaces. The correction works by dividing each pixel in the image by its counterpart in the master flat-field. To understand this, consider the effect of a dust-spot: as well as producing a blot on each image, it also appears as a dark patch (i.e. lower intensity number) in the same position in the flat field - so when you divide the raw frame by the flat field, this area will be reduced less (i.e. boosted in intensity) compared with the surroundings – and so the “flatness” of the image is restored!

Once you’ve got all these calibration images stored, just draw a box around a “dark” area of your first raw image, enter the names of the calibration files in the boxes in the Preprocessing..Automatic preprocessing (1) menu:
menu.jpg (25.8 KiB) Viewed 16345 times

And IRIS will convert your series of raw images into a sequence of calibrated ones, ready for alignment (as explained earlier).

For more detailed instructions, see the on-line IRIS “roadmap” tutorial:

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Re: IRIS - removing "stripes"

Post by rwilkinson » Sat Mar 12, 2011 8:42 am

Here's a handy feature which we've discovered this week - the ability to remove nasty stripes from a webcam image, just like this:
m82_carl1.jpg (163.76 KiB) Viewed 16345 times
It looks like a nasty problem, but all is not lost thanks to one of the advanced features in IRIS...
Since these stripes are periodic (repeating regularly), then they show up as discrete points in mathematical operation called a Fourier Transform - you don't need to understand the maths, just type FFTD X Y in the IRIS Command window. Then the periodic features (the diagonal stripes) show up as pairs of points (replicated in the opposing quadrant of the X transform plane):
fft.jpg (25.53 KiB) Viewed 16345 times
Now these can be removed by drawing boxes over them with the cursor and using FFILL 0 to paint them black. You only need to do this to one of each group, and then their partners are automatically mirrored:
fft2.jpg (25.56 KiB) Viewed 16345 times
Then save this new image as X1, and then apply an inverse transform using FFTI X1 Y
Then you'll find that the diagonal stripes have been removed, as if by magic:
m82_carl.jpg (17.2 KiB) Viewed 16345 times
And you may also have spotted that the two "pixel-trails" have vanished too. These were caused by two "hot pixels" on the CCD, which appear in the same position on each sub-frame, and so are converted to trails after alignment and stacking - they then paint a line showing the tracking error of your mount!
Anyway, IRIS can remove them easily enough - just draw a box around them with the cursor and use the MAX command (here, MAX 120) and they're history!



Post by dean_kos » Mon Mar 14, 2011 8:41 am

Your seriouisly on the road to getting a knighthood Ross .... :D :D



Post by dean_kos » Sun Jun 05, 2011 7:52 pm

How on earth do I get cr2 images from a canon 1000d to load into iris or registax ??? I have tried converting them to bitmaps but when i load them in they are huge !!! Any tips gratefully accepted as im getting nowhere fast with processing the images from this camera .......

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Post by rwilkinson » Sun Jun 05, 2011 8:43 pm

dean_kos wrote:How on earth do I get cr2 images from a canon 1000d to load into iris ???
You first need to select one of the Canon models on the Camera Settings menu and then you can import the RAW files.

I suggest that you study the excellent step-by-step "Diamonds from the Rough" IRIS primer: ... _iris.html
(this website seems to be down at the moment, but I've put a copy in the Software section of our Members' Area).

It's also covered in the IRIS tutorial: ... c13_us.htm
but this assumes a lot of background knowledge, whereas the first reference has more detailed instructions.
Both use a Canon camera as their worked example. :)

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Post by DRatledge » Mon Jun 06, 2011 10:16 pm

If you are struggling with the IRIS tutorial you can just load a single file with
File>Load a Raw File
It will be huge - all those pixels!

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