RAW vs JPEG - why?

[mikehab]

I'm sure this has probably been asked many times before ( I did a quick search and couldn't find anything ) - so apologies .... but why is it recommended to take RAW images rather than JPEG for DSO imaging?

Do the benefits of RAW really outweigh the "ease-of-use" of a Large, minimal comression, 18Meg JPEG? What am I missing out on by taking JPEG rather than RAW?

I personally find RAWs a bit of a pain do deal with - least of all because none of the graphical packages I use on a day-to-day basis can handle RAWs - so I end up having to use some converter to convert them to DNG(?) format first so that I can see whether the shots I have taken are actually any good and even worth stacking in the first place.

Maybe I should adopt some new graphical processing package that can handle Canon RAWs directly (any suggestions as to which one would be most welcome...) ... but I would like to feel confident that the benefits of dealing with RAWs are really worth it...

Go on .... convince me.... ;-)

Many thanks,

Mike

[Cath]

Hi Mike

The problem with JPG is that it's a 'lossy' compression - it compresses your image data whilst at the same time corrupts some it in the process (jpeg compression artifacts).

With RAW the image is not compressed using lossy compression (though they do normally use a lossless compression which is fine) and the image data is as it was in the camera, no data corruption. So the RAW image format retains your image data (pixels) without messing it up.

[GaryG]

Hi Mike,

I agree with the above and would like to add that my understanding is that jpegs are 8 bits (256 shades) per colour per pixel (to give a 24bit colour image) where as most dslr's currently spit out 14bits (16000+ shades) per colour per pixel in their raw file.

To do your DSO stacking DeepSkyStacker can read most raws (just make sure you have the camera drivers loaded) and when it's complete the stacked frame can be saved as TIFF or FIT for loading into the processing package of your choosing.

Gary

[burger]

There really is no comparison in terms of quality end results.

I have taken almost black raw images and in photoshop adjusted the exposure to reveal perfectly exposed images.

With a jpg it would just be a black screen.

Yes it is faffy but worth the extra time spent processing

[JG777]

Cath nails the best reason to use raw, that with a jpeg you have allowed the camera to do a lot of the processing and much of the data has been discarded, never to be retrieved either. Raw gives you a very large safety net in as much as non destructive editing, not to mention the 2 or 3 stops of adjustments available between highs and lows. That is a fair bit of latitude to mess with. To display a raw file on your computer with its native software, say for instance windows viewer you will need to download the canon codec. I see the problem you might have with specialist astro software where conversion is required. The other aspect of raw is the ability to be able to re-visit a file at a later date when software gets updates and improvements. Finally for normal photography especially with a raw file you can adjust the white balance to anything you like ( again non destructive edits) which is a hard if not impossible thing to do with a jpeg.

The Adobe DNG converter is quite good, it can convert batch files IIRC?

[JamesF]

By the time a camera spits out a JPEG I believe the firmware will have applied white filters and other non-reversible transforms to the image. It's much better to have the (as far as possible) unmodified data so that you are in control of how it is processed rather than the firmware of a camera, particularly one that is not tailored towards astrophotography.

When I first starting using a DSLR for imaging I did some tests processing RAW and JPEG versions of the same while light solar full disc exposures and I felt there was a clear difference between the two with the RAW versions having much better definition.

James

[allcart]

I agree with all the above, and am surprised that you are not making use of Canon's DPP software that comes with the camera. You can play to your hearts content, save the changes and then use the raw files for stacking with DSS.

[ollypenrice]

You can't process JPEGs. They look OK when you take a processed image and convert it to JPEG but if you try to process (which often means emphasize) a JPEG you will process (emphasize) all the artefacts it has introduced.

Olly

[Jessun]

Here are some more general tips on DSLR settings by Jerry Lodriguss:

http://www.astropix.com/HTML/I_ASTROP/SETTINGS.HTM

/Jesper

[Pete Presland]

Cath nails the best reason to use raw, that with a jpeg you have allowed the camera to do a lot of the processing and much of the data has been discarded, never to be retrieved either. Raw gives you a very large safety net in as much as non destructive editing, not to mention the 2 or 3 stops of adjustments available between highs and lows. That is a fair bit of latitude to mess with. To display a raw file on your computer with its native software, say for instance windows viewer you will need to download the canon codec. I see the problem you might have with specialist astro software where conversion is required. The other aspect of raw is the ability to be able to re-visit a file at a later date when software gets updates and improvements. Finally for normal photography especially with a raw file you can adjust the white balance to anything you like ( again non destructive edits) which is a hard if not impossible thing to do with a jpeg.

The Adobe DNG converter is quite good, it can convert batch files IIRC?

an excellent explanation, i could not have put it better!

[Paradox]

Always use raw from my DSLR as CA lateral and longitudal is the enemy of my pictures, even sometimes there with my very good lenses, the camera can PP some out in jpeg process but back at the PC the software does it so much better for me.

Clarisse.

[mikehab]

A huge thankyou to everyone who has responded so far - the message seems clear and consistent .... and RAW clearly wins. I'm definitly going to have to bite the bullet.

Jesper - thanks for the link to that Jerry Lodriguss article (http://www.astropix....OP/SETTINGS.HTM) - very useful indeed.

Alan - for some reason I completely ignored the Canon DPP software that came with the camera. I'm so stuck in my ways of using PhotoShop (including PictBridge) that I didn't really want to learn a new s/w package - but I will certainly give it a go now.

Many thanks all.

Mike

[DaveS]

The original DPP (That came with my 5D) was indeed barely adequate, but the latest version is pretty darn good with a dust removal stamp tool, angle adjustment / cropping and even HDR in the latest version. If they ever add layers, then PS is history

[mikehab]

You'll be glad to hear that I bit the bullet and had my first session last night taking RAWs rather than JPEG. I also installed DPP so that I could view the RAWs which helped hugely. Managed to grab a few shots of the ISS passing over and stacked 4 of them in DSS to produce the following...

DPP makes the whole RAW process a lot easier - I can't believe I never installed this in the first place, and I also found that DeepSkyStacker seemed a lot happier with RAWs than it does with JPEGs - so that's another bonus.

Thanks,

Mike

[JG777]

Nice image Mike, glad you got things sorted out. DPP might not be photoshop in terms of features but it is very good at what it does and I have heard many Canon users say it is all they need. Once you get used to raw it is very hard to go back to jpegs.

[peem]

Hi , Having read all your comments i have decided to stop using jpeg and use raw . One question . On the canon 50d thre are 3 settings . Raw , sraw1 and sraw2 which are full size , half and quarter size files . Has anyone tried the last two . Thanks