Just for Fun No C&C will be given: Can we 'see' a raw file?

Just passing interest; no need to reply unless you're so overcome with excitement that you can't help yourself.
Those who are interested in such things will have seen it before; those who aren't won't be.

At one time I would have said "No of course you can't view a raw file because it's only a collection of data representing the amount of light falling on each sensel". But then a grayscale image is only a collection of brightness values. What if I could extract the raw data and use it to construct a grayscale TIFF? I fiddled about, on and off, for a week or so and having proved that it could be done promptly forgot about it.
Then last year I was trying out a gui for the latest version of DCRaw and found it would do exqactly what I'd tried to do a couple of years previously.
If you choose 'Document mode no scaling' DCRaw just writes the raw data to the output file with no demosaicing.
The 16-bit linear TIFF (-D -4 -T) closely resembles a picture of a black cat in a coal cellar, but an 8-bit TIFF with a gamma curve applied (-D -T) provides a recognisable image.

Here's a 100% crop:



And here's part of it zoomed in:




Regards,

Stuart

Hi, Stuart,

StuartRae said:

Just passing interest; no need to reply unless you're so overcome with excitement that you can't help yourself.
Those who are interested in such things will have seen it before; those who aren't won't be.

At one time I would have said "No of course you can't view a raw file because it's only a collection of data representing the amount of light falling on each sensel". But then a grayscale image is only a collection of brightness values. What if I could extract the raw data and use it to construct a grayscale TIFF? I fiddled about, on and off, for a week or so and having proved that it could be done promptly forgot about it.
Then last year I was trying out a gui for the latest version of DCRaw and found it would do exqactly what I'd tried to do a couple of years previously.
If you choose 'Document mode no scaling' DCRaw just writes the raw data to the output file with no demosaicing.
The 16-bit linear TIFF (-D -4 -T) closely resembles a picture of a black cat in a coal cellar, but an 8-bit TIFF with a gamma curve applied (-D -T) provides a recognisable image.

Click to expand...

Thanks for the information on those operations.

I've never actually worked with DCRaw, although I have recently done a lot of analysis on information derived by others (Laurent Clévy, for one) from its code.

Once can get a similar presentation using the image manipulation and analysis program Iris, which is widely used by astrophotographers but can be quite useful beyond that field.

Thanks Doug.

I've never actually worked with DCRaw.....

Click to expand...

Conversely, although I know of Iris I've never looked at it.

When I first used DCRaw it had few options, but when I looked at it again last year it had sprouted many more. A full list can be found here

If you're not a command-line junkie there's a GUI for it here

Regards,

Stuart

Hi, Stuart,

StuartRae said:

Thanks Doug.


Conversely, although I know of Iris I've never looked at it.

Click to expand...

If you are intersted, here is its home:

http://astrosurf.com/buil/us/iris/iris.htm

If you're not a command-line junkie there's a GUI for it here

Click to expand...

Thank God for all the guys who develop GUIs for command-line software!

Thanks.

Best regards,

Doug

Hi Doug,

I've neglected to thank you for the link to Iris. My excuse is that my back went twang while putting my socks on, since when I've been unable to concentrate on anything other than how I'm going to get out of this chair.

Yes, it seems to provide a very similar raw + gamma image but not the really linear raw of DCRaw.

To complete the set, here are a few more images.

1. The really linear raw. If your monitor black-point is set accurately you can just make out the boundary between hills and sky. (the -D switch - document mode without scaling)



2. Document mode (-d) presumably with scaling. Is the correct term 'normalisation'?



3. The final RGB output. DCRaw does a fine job with well exposed images.



Regards,

Stuart