EXIF Exposure Bias

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EXIF Exposure Bias

Postby jarhtmd » Wed Jun 20, 2007 4:21 am

I just returned from a photo trip to China & shot a ton of pictures. I just downloaded BRU 2.5.4.2 & I appreciate your revision for adding EXIF exposure bias (%eb). However, I am confused by the results that I'm getting. All of my "unbracketed" digital images are shot with -1/3 bias. When I bracket (3 shots per image), I get biases such as -1/3, -6/3 & 4/3 (as shown in the file info by Photoshop). I was expecting to see the same suffix (added by BRU) for all -1/3, all -6/3, all 4/3, etc. That did not happen. My intent (in most cases) is to convert (in a separate pass) all of BRU's suffixes for -6/3 (or whatever I underexposed) to something simple like (-) and overexposures to (+), etc. The actual exposure bias isn't important in (most of) my final filenames, but I do need to distinguish the amounts because I don't consider my usual -1/3 to be a "bias".

I got the following (sorry for the cluttered look). Note: 3b, 6b, 13b, 15b, 20b, 25b, 30b = -1/3; 4b, 5b, 6b, 8b = 4/3; 50b, 60b, 100b = -6/3

File. Suffix.Exp-Bias. . . . . File. . . Suffix. . . . . Exp-Bias
1. . . 3b. . .-1/3. . . . . . .7. . . . . 13b. . . . . -1/3
2. . . 3b. . .-1/3. . . . . . .6. . . . . 15b. . . . . -1/3
3. . . 3b. . .-1/3. . . . . . .10. . . . .15b. . . . . -1/3
4. . . 3b. . .-1/3. . . . . . .16. . . . .15b. . . . . -1/3
5. . . 6b. . .-1/3. . . . . . .19. . . . .15b. . . . . -1/3
6. . .15b. . .-1/3. . . . . . .8. . . . . 20b. . . . . -1/3
7. . .13b. . .-1/3. . . . . . .9. . . . . 20b. . . . . -1/3
8. . .20b. . .-1/3. . . . . . .22. . . . .20b. . . . . -1/3
9. . .20b. . .-1/3. . . . . . .11. . . . .25b. . . . . -1/3
10. . 15b. . .-1/3. . . . . . .12. . . . .25b. . . . . -1/3
11. . 25b. . .-1/3. . . . . . .13. . . . .30b. . . . . -1/3
12. . 25b. . .-1/3. . . . . . .1. . . . . .3b. . . . . -1/3
13. . 30b. . .-1/3. . . . . . .2. . . . . .3b. . . . . -1/3
14. .100b. . .-6/3. . . . . . .3. . . . . .3b. . . . . -1/3
15. . .8b. . . 4/3. . . . . . .4. . . . . .3b. . . . . -1/3
16. . 15b. . .-1/3. . . . . . .5. . . . . .6b. . . . . -1/3
17. . 50b. . .-6/3. . . . . . .18. . . . . 4b. . . . . .4/3
18. . .4b. . . 4/3. . . . . . .21. . . . . 5b. . . . . .4/3
19. . 15b. . .-1/3. . . . . . .24. . . . . 6b. . . . . .4/3
20. . 50b. . .-6/3. . . . . . .15. . . . . 8b. . . . . .4/3
21. . .5b. . . 4/3. . . . . . .14. . . . 100b. . . . . -6/3
22. . 20b. . .-1/3. . . . . . .17. . . . .50b. . . . . -6/3
23. . 60b. . .-6/3. . . . . . .20. . . . .50b. . . . . -6/3
24. . .6b. . . 4/3. . . . . . .23. . . . .60b. . . . . -6/3
jarhtmd
 
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Location: Maryland, USA

Postby Admin » Wed Jun 20, 2007 7:44 am

Could you try to explain it differently please, as I really don't follow your table. Probably best to show it as:

Frame 1 - shot as -1/3, BRU shows as -1.3
Frame 2 - shot as -1/3, BRU shows as -1.3


etc.

The actual EV value is held as adecimal number within the file, so if BRU shows it differently to Photoshop then the two programs must be interpreting things differenty.

Many thanks.



Jim

PS It'll be Monday before I can reply now.
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Postby jarhtmd » Wed Jun 20, 2007 2:00 pm

Actually, I expected BRU to translate & represent the exposure bias differently than Photoshop. Since I use only a very few biases, I expected to set up my own little chart after determining “thisâ€
jarhtmd
 
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Joined: Fri Oct 27, 2006 8:53 pm
Location: Maryland, USA

Postby jarhtmd » Thu Jun 28, 2007 6:31 pm

BRU Help says:
If you are processing JPEG files, you can also extract certain EXIF tags. These are specified using substitution tags, which you key into the Prefix, Insert or Suffix boxes (box 7). The tags current available are:
%a - Aperture
%c - Comments
%e - Exposure
%eb - Exposure Bias
%f - Focal Length

When I put %e into box7 (see below), I get exposure. When I put %eb, I simply get “bâ€
jarhtmd
 
Posts: 36
Joined: Fri Oct 27, 2006 8:53 pm
Location: Maryland, USA

Postby jarhtmd » Fri Jul 06, 2007 9:47 pm

HELP! As I understand BRU Help; to extract EXIF tags when processing JPEG file,( in box 7) I should use "%e" for Exposure or "%eb" for Exposure Bias. When I enter "%eb" (no quotes), I simply get the letter “bâ€
jarhtmd
 
Posts: 36
Joined: Fri Oct 27, 2006 8:53 pm
Location: Maryland, USA

Postby jarhtmd » Tue Jul 17, 2007 5:52 pm

When processing JPG files to extract Exposure (EXIF data) I use "%e" (no quotes) in box 7. I get results like:

Img_0001.jpg changes to Img_0001-3.jpg
Img_0002.jpg changes to Img_0002-15.jpg
Img_0003.jpg changes to Img_0003-13.jpg
Img_0004.jpg changes to Img_0004-20.jpg

When I want to extract Exposure Bias I use "%eb" (no quotes) & get the letter “bâ€
jarhtmd
 
Posts: 36
Joined: Fri Oct 27, 2006 8:53 pm
Location: Maryland, USA

Postby Admin » Tue Jul 17, 2007 6:55 pm

I'm not sure, since it works for me. Suggest you email me a sample photo.


Jim
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Postby jarhtmd » Wed Jul 18, 2007 2:29 am

What email address shall I send it to?
jarhtmd
 
Posts: 36
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Location: Maryland, USA

Postby Admin » Wed Jul 18, 2007 7:38 am

paypal@jimwillsher.co.uk should be fine.


Jim
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Postby Admin » Wed Jul 18, 2007 9:08 pm

Ok, I think I've got to the bottom of it. The %e is being processed before the %eb, so the %eb is being ignored. I'll change it to %xb for the next release.

For reference, the exposure bias is shown as 1.333 (for 1 1/3), 0.333 (for 1/3), 0.666 (for 2/3) etc.


Jim
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