Canon sx200 is: Getting wrong Exposure Values while bracketing shots - Hello, I'm a NEWBIE - HELP!! (Newbies assistance, User Guides and thank you notes) - CHDK Forum
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Canon sx200 is: Getting wrong Exposure Values while bracketing shots

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Offline erat

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Canon sx200 is: Getting wrong Exposure Values while bracketing shots
« on: 13 / November / 2010, 16:15:19 »
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I'm shooting hdri and getting varied results. When hdr-merging in photoshop, I can see that several shots are using same EV, which causes crazy tones in HDR.

In Photomatix I can manually set EV, but I prefer using PS over Photomatix, because of more control. Photomatix would be better for initial hdr, but it doesn't save 32bit.

How could I fix EV's before merging to hdr? Or prevent this wrong EV from happening.

Here's a sample: http://img843.imageshack.us/img843/5012/scandicsmall.jpg

- eRat
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Offline reyalp

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Re: Canon sx200 is: Getting wrong Exposure Values while bracketing shots
« Reply #1 on: 13 / November / 2010, 16:28:14 »
Quote from: erat on 13 / November / 2010, 16:15:19
I'm shooting hdri and getting varied results. When hdr-merging in photoshop, I can see that several shots are using same EV, which causes crazy tones in HDR.
Do you mean that several images actually have the same exposure, meaning that bracketing is not working ? Or is photoshop is trying to determine the EV from some other source (probably exif) and getting the wrong value ?

In general, exif are not reliable when CHDK overrides the exposure. The canon maker notes are more likely to be correct. I'd suggest using some tool to inspect the exif of the problem images.
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Offline erat

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Re: Canon sx200 is: Getting wrong Exposure Values while bracketing shots
« Reply #2 on: 13 / November / 2010, 17:47:15 »
Images have different exposure, so I think bracketing is working right. Photos seem to have correct exposures. So I think exif is written incorrectly. I'll check tomorrow the images one by one to see what exposure values have been written in the metadata.
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Offline fudgey

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Re: Canon sx200 is: Getting wrong Exposure Values while bracketing shots
« Reply #3 on: 14 / November / 2010, 05:26:53 »
CHDK currently doesn't have any control over JPEG EXIF tags. Assuming you used CHDK to override Tv, all the Tv tags will be incorrect except Canon's proprietary binary encoded MakerNote tags. Something like

exiftool -overwrite_original_in_place -EXIF:ExposureTime<MakerNotes:ExposureTime *.JPG

should probably fix things for you (copy the makernotes Tv value to one of the regular exif tags that photoshop probably reads). A common problem, Barney's old autoexif tool may still be somewhere out there, search the forum & wiki and see http://chdk.setepontos.com/index.php?topic=138.0
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