Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5
raw file clipping
#1
a quick question - i thought i'll ask here first but maybe not a right question for this site so much, as it's not about lenses - but i see many knowledgable bods here, although not so many sony people (but that's true everywhere) -



so - if there is anyone here familiar with a900 (or 850 i guess) - or maybe other cameras too -



i'm having a concern about the RGB (especially blue) channels being pushed into clipping in raw conversion with a standard conversion of a file (via both ACR and C1) - it is possible to adjust to bring it out from raw unclipped and then realign the blacks/whites in Ps and end up with a very similar (or better) graded picture with correctly aligned unclipped RGB's - but why is it so? -



is it me, or is it the current files out of my camera? - has anyone else noticed this? - or is this normal for other camera's files too?



thanks in advance,

keith
#2
Hi Keith,



Can you maybe show some samples, or even put up some samples for us to download and check out? It is very hard to discuss this without actually being able to see or work with a file as you describe. It could be the result of many things, like WB out of whack, very bright blue skies, overcast skies with a bright sun behind the clouds, early morning pictures before the sun is out with some overexposure, just simple overexposure with blue as the main light, etc.



The things I normally do in ACR is correct (over)exposure, and do some curves, and nothing else, before saving to a 16-bit tif file, so as to preserve most if not all of the DR, prior to getting to work on it in proper PP.



Of course, you could always try to expose to the right, IOW, make sure that nothing (or virtually nothing) gets clipped on the bright end, as generally digital cameras are much better at bringing the dark parts to life than film is/was, but it is not possible at all to bring anything truly overexposed back, where film has more latitude.



Anyway, looking forward to see some samples so we can help you more specifically with your problem.



Kind regards, WIm
Gear: Canon EOS R with 3 primes and 2 zooms, 4 EF-R adapters, Canon EOS 5 (analog), 9 Canon EF primes, a lone Canon EF zoom, 2 extenders, 2 converters, tubes; Olympus OM-D 1 Mk II & Pen F with 12 primes, 6 zooms, and 3 Metabones EF-MFT adapters ....
#3
hi wim and thanks for this - yes i'll put a more comprehensive report with some screen shots of waveforms etc (possibly from C1) - not sure where i can post an actual raw file right now, but i'll look at that too - this might take a little while,

thank you,

k
#4
hi wim,



here is an example picture of a local Acacia, this branch was blowing about in a strong wind and the only reason i didn't walk away was that i didn't have to pay for the neg, so focus could be better - but anyway the exposure/white balance appears fine to me - so -



first screen shot from C1 shows the standard RGB wfms. in which the blue channel is rather cramped to the left and in fact clipped -

[Image: 980409193_Lrf8x-O.jpg]



the second screen shot shows my tweaked levels so that any info in blue (which is heading off stage left) is available in the output tiff -

[Image: 980409128_JNPME-O.jpg]



3rd is Ps in of the colours from the 1st tiff -

[Image: 980409077_D5eHL-O.jpg]



4th Ps in colours of my tweaked version -

[Image: 980409081_d3GTA-O.jpg]



5th my reset colour levels - nice and neat and tidy and close'ish (for me) -

[Image: 980409102_xcMxB-O.jpg]



6th an output jpeg shows a comparison with a diagonal (topright/bottomleft)mask between both conversions (top is my adjusted colour levels which for me gives a more neutral balance in the extreme blacks which i prefer, otherwise they are close) -

[Image: 980417326_yeMFY-O.jpg]



so, for me this adjustment is not a difficult or slow thing to do, and i feel i could set up a standard run if needed - but it seems maybe something wrong, and both C1 and ACR show the same thing, so is it normal for raw and i shouldn't be worrying about it, or is something incorrect do you think -



if you would still like to look at this raw file for yourself i think i can put it up at the deposit files site for you, or if you have a site to upload to - just ask -



thanks,

k
#5
[quote name='anyscreenamewilldo' timestamp='1282598727' post='2060']

a quick question - i thought i'll ask here first but maybe not a right question for this site so much, as it's not about lenses - but i see many knowledgable bods here, although not so many sony people (but that's true everywhere) -



so - if there is anyone here familiar with a900 (or 850 i guess) - or maybe other cameras too -



i'm having a concern about the RGB (especially blue) channels being pushed into clipping in raw conversion with a standard conversion of a file (via both ACR and C1) - it is possible to adjust to bring it out from raw unclipped and then realign the blacks/whites in Ps and end up with a very similar (or better) graded picture with correctly aligned unclipped RGB's - but why is it so? -



is it me, or is it the current files out of my camera? - has anyone else noticed this? - or is this normal for other camera's files too?



thanks in advance,

keith

[/quote]

Clipping occurs on the left, Keith. In your example we just see that in the very dark part in the image the blacks have a blue tone/cast (on the right). You can not talk about clipping there, clipping in when the photo diodes collect so much photon's that they are full and the extra photons can not be registered anymore. On the right we are talking about (almost) no light.



That is after RAW conversion.

This (always the blue channel dominant in blacks) may well be because maybe your/the A900 has more noise in the blue channel, and noise shows up more in the dark or underexposed parts.

I would not worry about it, as it clearly does not mess with your colour balance.



And if indeed the blue channel shows noise in the shadows, that is then nothing a bit of NR can not cure.



If youdo not want anything to be pushed into the shadows, just lower contrast. That will bring the right data into play.



But basically, I think you may be worrying about nothing.
#6
[quote name='Brightcolours' timestamp='1282641234' post='2091']

. . . . basically, I think you may be worrying about nothing.

[/quote]

thanks for this Bc -



i was hoping that this was my mistake, so this is good - processing as per normal is easy - so, sorry about the long post about an illusion, but i'm relieved, thank you,

k
#7
[quote name='anyscreenamewilldo' timestamp='1282644408' post='2096']

thanks for this Bc -



i was hoping that this was my mistake, so this is good - processing as per normal is easy - so, sorry about the long post about an illusion, but i'm relieved, thank you,

k

[/quote]



Hi Keith, I was away for the day, but I do agree with Brightcolours here. I don't think there is really anything to worry about. You could maybe try some noise filtering to see if it helps a little.



Another possibility is to see if setting WB to a slighly higher Kelvin value before conversion to tif or jpeg helps. It could be that the WB metering of the camera was misled by the enormous amount of yellow in the picture. The WB metering in a camera is sometimes too sophisticated (read: tries to correct in a clever way a little too much at times). A few 100 degrees should be plenty in this case.



Kind regards, WIm
Gear: Canon EOS R with 3 primes and 2 zooms, 4 EF-R adapters, Canon EOS 5 (analog), 9 Canon EF primes, a lone Canon EF zoom, 2 extenders, 2 converters, tubes; Olympus OM-D 1 Mk II & Pen F with 12 primes, 6 zooms, and 3 Metabones EF-MFT adapters ....
#8
What you should remember is that the rule of not clipping the histogram is more of a guideline - sometimes it's ok to even clip in the highlights, if you're making a purposefully high key photo, or if the sun is in the frame. In most cases it's ok to clip in the shadows, where it's hardly noticable - in fact I frequently up the black point a bit to add more punch, without looking at whether the histogram clips. My rule of thumb is that shadow clipping just happens, but highlight clipping should only happen when you want it to.



That said, it is concievable that you could have a tone with, in this case, just a slight bit of blue in it, where if you cut the blue out you end up with a slightly different tone in the darker areas. Whether and how much this happens depends entirely on what tool you use for your adjustments, some are very coarse and some are very sophisticated. But in general, you should let go of the illusion that the histogram is telling you how good the picture is and just look at the picture. The histogram can point you at potential problems, but in the end it's how the picture looks that matters. Your viewers will not have a histogram at hand to judge the picture by, after allSmile



-Lars
  


Forum Jump:


Users browsing this thread:
1 Guest(s)