Author Topic: Image format questions  (Read 2231 times)

Offline Jack Harvey

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Image format questions
« on: 2008 May 16 15:33:08 »
I have two questions about image format in PixInsight.  I think I know the answers but would like to hear it from the pros.

1.  When assembling master images in CCDStack I produce standard deviation mean masters and often then assemble a RGB image.   I have two formats that I can save in before I bring them into PixInsight for processing.  Either 32 bit IEEE floating point fits or 16 bit tiff.  I assume the fits is the best option?

2.  If you have processed an image say in 32 bit fits and then decide to save it in 16bit tiff BUT accidentally save it first as a JPEG (8 bits), how do you then recover from this mistake and be able to save in 16 bit tiff?  Or do you now have a 8 bit image and can only save as 8 bit tiff?

Thanks for the upcoming answers<G>
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Offline Carlos Milovic

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Image format questions
« Reply #1 on: 2008 May 16 18:05:36 »
Hi Jack

1.- Yes, in this case FITS is the best option. Unless it is a very large image, always use 32bits for processing. It may be a lot more than needed just to store data, but makes things much better when working the data. Additionally, many processes in PixInsight will use internal 64bits accuracy when handling 32bits images.

2.- The answer to this question will generally depend on the software that you are using. In PixInsight there is no need to worry (as long you don't close the image). Views (images loaded into Image Windows) are independ objects from image files. This means, if you use the "Save as" option to write a new image, with a different bit depth, this will not affect the depth of your View. Similarly, if you write an image in JPEG lossy format, you won't get any artefacts from the compression, because the view is not affected by this operation.
The only way to change the bit deph of a View is to use the SampleFormatConversion process.

Having said that, if you open a jpeg image, certainly you'll be able to write it as even a 64bits image, if you like. But, you'll have only 8bits of real data. Indeed image processing may increase the number of levels, but the data loss is unrecoverable.
Regards,

Carlos Milovic F.
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Offline Jack Harvey

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format
« Reply #2 on: 2008 May 16 18:41:30 »
Carlosw  Thanks for the answer.  I figured the 32 bit wa best but di d not know the answer to the second part.  That is great!  Have a good weekend.  I am sitting down to a nice steak and a bottle of Concho Y Toro (Chile)<G>.
Jack Harvey, PTeam Member
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Offline Carlos Milovic

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Image format questions
« Reply #3 on: 2008 May 16 19:02:23 »
Concha y Toro ;)

Thanks! I still have a few images to process, so I think that I'll be on the computer when not training :P (martial arts)

Enjoy the wine!
Regards,

Carlos Milovic F.
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PixInsight Project Developer
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