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Author Topic: How to handle/remove color cast of digital backs  (Read 9291 times)

acg

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How to handle/remove color cast of digital backs
« on: March 31, 2011, 11:47:18 pm »

I am new to MF digital backs. I just got an Alpa 12 TC with a Leaf Aptus 75, with a Schneider digitar 35mm f/5.6 XL. The photos from that are very sharp. However, when shooting a white wall indoor, the colors became very chaotic, with hints/cast of green / purple here and there.

Any suggestions on how to handle the color cast?

Thanks!
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pixjohn

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Re: How to handle/remove color cast of digital backs
« Reply #1 on: March 31, 2011, 11:52:34 pm »

Both the Leaf and Phaseone software have lens calibration built in to remove lens cast. You need to shoot the white plexi disc that came with the back or just use a piece of white plexi.  You do need to shoot it at the same movements and f stop the image was shot at. I believe he Leaf website should have all the directions.
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acg

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Re: How to handle/remove color cast of digital backs
« Reply #2 on: April 01, 2011, 01:11:08 am »

Thanks for the reply. It seems I will need to connect my camera to my computer to do the calibration. Unfortunately my computer does not have a firewire port. I am going to find an adapter to connect these two and try it out.
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yaya

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Re: How to handle/remove color cast of digital backs
« Reply #3 on: April 01, 2011, 02:27:40 am »

Thanks for the reply. It seems I will need to connect my camera to my computer to do the calibration. Unfortunately my computer does not have a firewire port. I am going to find an adapter to connect these two and try it out.

No need for a computer.

Set the back's compression to "Lossless"
Shoot with a White diffuser filter (or a piece of white perspex) as John suggested. It is important to do one whenever you change aperture and to compensate by adding 2 stops of exposure time.

I'm assuming that no firewire port means it's a PC, so you have to use Capture One Pro:
Select the white image and in the lens tool tab, select Analyse from the LCC drop-menu, save it let's say with the f-stop number. Then select all the images that you've taken with the same aperture and apply this correction by selecting it from the same drop-menu

You can opt to apply fall off correction as well at the same time

Note that this function does not exist in Lightroom/ ACR so if you use these you will have to do the correction in Photoshop, which si time consuming and probably not as good.

Enjoy your new back!

Yair
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acg

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Re: How to handle/remove color cast of digital backs
« Reply #4 on: April 01, 2011, 02:40:16 am »

Thanks Yair!

I am using a MacBook air actually. (I know it is not that fast, but useable to me.)
So I am using leaf capture v11. The menu has a "camera" item, and there is a "create lense calibration file" under it. However it is disabled.

Any suggestions on how to use LC to correct the colors? Thanks a lot!

No need for a computer.

Set the back's compression to "Lossless"
Shoot with a White diffuser filter (or a piece of white perspex) as John suggested. It is important to do one whenever you change aperture and to compensate by adding 2 stops of exposure time.

I'm assuming that no firewire port means it's a PC, so you have to use Capture One Pro:
Select the white image and in the lens tool tab, select Analyse from the LCC drop-menu, save it let's say with the f-stop number. Then select all the images that you've taken with the same aperture and apply this correction by selecting it from the same drop-menu

You can opt to apply fall off correction as well at the same time

Note that this function does not exist in Lightroom/ ACR so if you use these you will have to do the correction in Photoshop, which si time consuming and probably not as good.

Enjoy your new back!

Yair
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Dick Roadnight

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Re: How to handle/remove color cast of digital backs
« Reply #5 on: April 01, 2011, 03:20:41 am »

I am new to MF digital backs. I just got an Alpa 12 TC with a Leaf Aptus 75, with a Schneider digitar 35mm f/5.6 XL. The photos from that are very sharp. However, when shooting a white wall indoor, the colors became very chaotic, with hints/cast of green / purple here and there.

Any suggestions on how to handle the color cast?

Thanks!
Back to basics...

How is the wall lit?

Have you set the White balance?
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yaya

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Re: How to handle/remove color cast of digital backs
« Reply #6 on: April 01, 2011, 03:21:54 am »

Thanks Yair!

I am using a MacBook air actually. (I know it is not that fast, but useable to me.)
So I am using leaf capture v11. The menu has a "camera" item, and there is a "create lense calibration file" under it. However it is disabled.

Any suggestions on how to use LC to correct the colors? Thanks a lot!


In the Process tab, select "mos" as the output format, then click "settings"

Check the box that says "lens calibration", select First or Last for the order of the images and the amount of falloff correction you would like to apply (I normally start fairly low, say 10-15%)

You can also check the "Save Compressed" box to save space (this is a lossless compression)

Set the destination folder, I always choose the same folder where the originals are so that I can see before/ after. The corrected file will carry the same name as the original with an "_1" at the end.

More about it in the Leaf Capture help menu: Select Help>Leaf Capture Help and once the HTML file opens, select search and type in "Lens"

Note that the corrected files are basically new raw files, you can then use them in any 3rd party software, archive them etc.

I also suggest that you register on our website so that in the future you can contact us directly for support: Support site link

Hope this helps

yair
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Doug Peterson

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Re: How to handle/remove color cast of digital backs
« Reply #7 on: April 01, 2011, 06:37:38 am »

Yair,

Sure that wasnt a typo? Lossless or compressed??

Other reasons LCC could be grey:
- You are running capture one express rather than capture one pro.
- the firmware of the aptus 75 is far out of date

If you bought from a dealer try should be there to help you through all these questions

Doug
Captureintegration.com
From iphone

yaya

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Re: How to handle/remove color cast of digital backs
« Reply #8 on: April 01, 2011, 07:06:13 am »

Yair,

Sure that wasnt a typo? Lossless or compressed??



Uploaded with ImageShack.us

Quote
Other reasons LCC could be grey:
- You are running capture one express rather than capture one pro.
- the firmware of the aptus 75 is far out of date
I think he meant in the software; It is greyed out if the back is not connected as this feature is for tethered work:

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MichaelEzra

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Re: How to handle/remove color cast of digital backs
« Reply #9 on: April 01, 2011, 09:06:19 am »

You can also use Rawtherapee as illustrated here:
http://www.luminous-landscape.com/forum/index.php?topic=50990.0

Works perfectly on any camera/lens as long as raw file format is supported (which is likely the case).
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yaya

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Re: How to handle/remove color cast of digital backs
« Reply #10 on: April 01, 2011, 09:55:10 am »

You can also use Rawtherapee as illustrated here:
http://www.luminous-landscape.com/forum/index.php?topic=50990.0

Works perfectly on any camera/lens as long as raw file format is supported (which is likely the case).

Interesting Michael but I'm guessing that the typical Mac user will not want to delve into coding and compiling software when there is a tried and tested solution offered by the manufacturer

Cheers

yair
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MichaelEzra

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Re: How to handle/remove color cast of digital backs
« Reply #11 on: April 01, 2011, 11:46:23 am »

There is a distribution of the compiled (and portable - no installation required)  RawTherapee hosted at http://www.rawtherapee.com/releases_head/
as well as here: http://rawtherapee.com/forum/viewtopic.php?t=1910  (always go to the last page of the frequently updated thread)
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acg

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Re: How to handle/remove color cast of digital backs
« Reply #12 on: April 01, 2011, 12:49:41 pm »

Back to basics...

How is the wall lit?

Have you set the White balance?

The wall was lit with fluorescent, not well lit. I used the wall for grey WB picker. Before and after the WB setting, the color casts were very visible.
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acg

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Re: How to handle/remove color cast of digital backs
« Reply #13 on: April 01, 2011, 12:51:01 pm »

Thanks Yair! I will try it tonight when I get home.

In the Process tab, select "mos" as the output format, then click "settings"

Check the box that says "lens calibration", select First or Last for the order of the images and the amount of falloff correction you would like to apply (I normally start fairly low, say 10-15%)

You can also check the "Save Compressed" box to save space (this is a lossless compression)

Set the destination folder, I always choose the same folder where the originals are so that I can see before/ after. The corrected file will carry the same name as the original with an "_1" at the end.

More about it in the Leaf Capture help menu: Select Help>Leaf Capture Help and once the HTML file opens, select search and type in "Lens"

Note that the corrected files are basically new raw files, you can then use them in any 3rd party software, archive them etc.

I also suggest that you register on our website so that in the future you can contact us directly for support: Support site link

Hope this helps

yair
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acg

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Re: How to handle/remove color cast of digital backs
« Reply #14 on: April 01, 2011, 12:54:40 pm »



Uploaded with ImageShack.us
I think he meant in the software; It is greyed out if the back is not connected as this feature is for tethered work:



That is the case. I guessed it was greyed out because the back was not connected.

BTW, is there a way to update the firmware on an Aptus 75?
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yaya

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Re: How to handle/remove color cast of digital backs
« Reply #15 on: April 01, 2011, 01:14:03 pm »

BTW, is there a way to update the firmware on an Aptus 75?

If it's an old/ used back then Leaf Capture 11.2.4 will provide the latest firmware for it

If it is a newly refurbished back then 11.4.5 might update it (depending on what you already have there)

Either way you need a FireWire connection to a Mac. Your dealer should be able to help you if you do not have access to FireWire

Yair
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Dick Roadnight

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Re: How to handle/remove color cast of digital backs
« Reply #16 on: April 01, 2011, 01:14:46 pm »

The wall was lit with fluorescent, not well lit. I used the wall for grey WB picker. Before and after the WB setting, the color casts were very visible.
There used to be a theory that conventional fluorescent light lacks green, and is bound to cause a colour cast... if you want to calibrate anything, it would be the last light source to choose, white balanced or not.
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yaya

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Re: How to handle/remove color cast of digital backs
« Reply #17 on: April 01, 2011, 01:20:44 pm »

There used to be a theory that conventional fluorescent light lacks green, and is bound to cause a colour cast... if you want to calibrate anything, it would be the last light source to choose, white balanced or not.

The colour cast here is a result of using the wide angle, non-retrofocal lens and the type of light source has little or nothing to do with it. That's why you need to use a diffuser filter, WB can be done afterwards
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acg

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Re: How to handle/remove color cast of digital backs
« Reply #18 on: April 01, 2011, 01:58:23 pm »

You can also use Rawtherapee as illustrated here:
http://www.luminous-landscape.com/forum/index.php?topic=50990.0

Works perfectly on any camera/lens as long as raw file format is supported (which is likely the case).

That is quite impressive!

The first image of "Before" is pretty much what I have now. :)
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yaya

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Re: How to handle/remove color cast of digital backs
« Reply #19 on: April 01, 2011, 03:10:14 pm »

There is a distribution of the compiled (and portable - no installation required)  RawTherapee hosted at http://www.rawtherapee.com/releases_head/
as well as here: http://rawtherapee.com/forum/viewtopic.php?t=1910  (always go to the last page of the frequently updated thread)

Is there a version to try on 10.6.X?
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