AUG
31
2008

Photo KDE Tutorial 1-3: White balance

I'm real sorry, but the images in this blog post were lost in a server move (kdedevelopers cannot host images), so I had to delete it altogether =(

Comments

please add this to docbook documentation


By shaforostoff at Sun, 08/31/2008 - 10:13

That will be troublesome to do. All screenshots are in english version, so translators would need to reproduce all steps one by one. Then draw the lines etc. Not sure how many would offer themselves to do that.

Then there's the part of "image rights" issues. I don't think those people would like for their faces to turn up in every distro's packages ;) so I'd rather replace those photos with others to avoid that.

And finally, the way it's written needs a few changes to become official docs.

The other option, is hosting tutorials elsewhere, and pointing to them from the application, but they'd be in english


By uga at Sun, 08/31/2008 - 19:22

That picture will never die....

Also, my face is actually as red as a strawberry in real life so you've done it all wrong!

(Nice work, I look forward to trying it out!)


By Mike Arthur at Sun, 08/31/2008 - 11:15

Here's a photo that I have been practicing on:
http://en.wikipedia.org/wiki/Image:Victoria_Crater,_Cape_Verde-Mars.jpg

I would love to see what you could do with her. I have been able to get some of the detail of Cape Verde (the overhand on the left) to show, but I ruin the rest of the photo in the process. I have seen renditions where the whole thing looks detailed. This would be a great photo to summarize your first three tutorials with, as I have used techniques from all three.

Thanks!


By dotancohen at Tue, 09/02/2008 - 13:22

Heh, there's much harder photos than that one, honestly ;)
You just need to fix the white balance to show the middle area gray. Sky then will get fixed, although I'm not sure about the real colors since I wasn't there taking the shot. One should never attempt fixing a white balance of a photo that somebody else took :P
Then rise shadows to uncover details from under the rocks on the left part.

Do you have an e-mail or contact page to submit the result to? your profile doesn't show any


By uga at Fri, 09/05/2008 - 00:11

Thanks, I have enabled the contact form:
http://www.kdedevelopers.org/user/6365/contact

Also, you can email me at <your-name-here><at>dotancohen<dot>com

I appreciate the tips, and I am enjoying learning the process. Thanks!


By dotancohen at Wed, 09/17/2008 - 19:36

Hi,

just some nitpicking about how to select the "white" area.

You shouldn't select an area which is very bright in the image, IOW make sure none of the channels (neither R nor G nor B) is 255 or very close to it (it may have been fully saturated but due to the image processing end up slightly below 255). If one of the channels is already 255 in the image, it probably wasn't exactly 255, but was clipped to the maximum value, so maybe the correct value would have been 300, but the range only goes up to 255. So choose a point which is more grayish, not white.
So I'm not sure the white T-shirt is the best choice, since it seems quite bright, in some places (according to kcolorchooser) red goes up to 253. So choose a point in a shadowed area of the T-shirt.

About the color picker: I don't know how it is implemented, but it shouldn't select a single point, but instead a small area, like 3x3. This will smooth away small variations in the "grayness" of the image. E.g. it could also be possible that some gray area gets slightly colored "stains" trough noise and JPEG compression. By using a small area instead of a single point this should give better results.

In the corrected image big parts of the T-shirt are almost 255-255-255. This means information has been lost. Ideally the overall brightness of the points shouldn't increase too much. So, I don't know how it is implemented. If the factors against red are calculated and then all points are multiplied with them, then the result would be very bright. Maybe this is what we see here. Maybe something more clever could be done. Maybe scaling everything to green (since this usually expresses the brightness quite good) ? Or calculating the brightness (sum of R + G + B ?) of the reference point and adjusting the factors so that it stays the same ?

Just some ideas...

Alex


By Alexander Neundorf at Tue, 09/02/2008 - 19:28

"You shouldn't select an area which is very bright in the image,"

Very right indeed. Sorry that I missed commenting that. I usually go for gray levels. Actually I clicked on the top part of the neck stripe, which is darker.

"I don't know how it is implemented, but it shouldn't select a single point, but instead a small area, like 3x3. This will smooth away small variations"

I wish it did that, but I believe all white balance colro pickers I've seen select a point instead. Not sure if for accuracy reasons or what. But yes, you are right, averaging would do a much better work. It's how those filter disks for white metering work. Can you report that to bugs.kde.org? I think it'd be a nice feature to implement to digikam.

"In the corrected image big parts of the T-shirt are almost 255-255-255. This means information has been lost."

Could be, but it may be that the original colors were so high that compensation wasn't at all possible. I haven't coded this plugin myself. I tried my best to fix it without overexposing it. Also notice that I haven't worked with full sized pictures, but samples provided online. It's much easier that those scaled versions have high compression and lack of detail.

Thanks for all the suggestions!


By uga at Wed, 09/03/2008 - 23:55