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Archive 2011 · Question Concerning change in Histogram
  
 
Image1
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p.1 #1 · p.1 #1 · Question Concerning change in Histogram


I ocassionally shoot using tungstens mainly because I have an extensive amount of accessories for them. I also perfer to shoot jpegs and I correct the color disbalance using Photoshop CS2 CURVES WHITE EYEDROPPER TOOL. Recently I looked at a histogram in a before and after and noticed the histogram goes from normal to ALMOST FLAT ...why does this happen? ...and how much damage is this causing the images quality?


Dec 14, 2011 at 04:17 PM
Peter Figen
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p.1 #2 · p.1 #2 · Question Concerning change in Histogram


A histogram is simply a graph of the pixel distribution in a given image. It can tell you if you have more or less a full range or if any major adjustments you made have possibly made the image prone to posterization. The vertical rise and fall of the histogram from left to right only indicates the number of pixels of a particular value, so that shape is entirely dependent on image content. There is no right or wrong.

That being said, correctly for incorrect color temperature illumination on a jpeg is asking for trouble. A much better method is to set the color temperature on your camera to match your lighting temp - usually somewhere between 2700K and 3200K for tungsten. You'll need very little if any correction when you do that.

An even better way is to shoot RAW files and set the color temperature in the RAW processing software. Shooting RAW lets you fine tune that color decision on a per image basis and can be more accurate than doing it in camera. It also acts on the full native camera data and is not nearly as prone to image degradation as making tonal moves on a jpeg.



Dec 14, 2011 at 05:02 PM
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p.1 #3 · p.1 #3 · Question Concerning change in Histogram


Thanks for the reply Peter! I'm now not as concerned about the histograms change and what it might be doing to the image quality. As for the color correcting I think I'm going to try your suggestion for in camera temp. change, my camera only offers Tungsten, Daylight, Etc. Settings, no actual Kelvin selections, And Raw files are unfortunately out for me due to this being an old camera that writes a Raw file so slow I still can't believe it! Thanks Again for the Help!


Dec 14, 2011 at 06:16 PM
Peter Figen
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p.1 #4 · p.1 #4 · Question Concerning change in Histogram


In that case, the Tungsten setting should get you much closer. Good luck with that.


Dec 14, 2011 at 06:52 PM
 

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p.1 #5 · p.1 #5 · Question Concerning change in Histogram


Just ran some test shots, Much much better whites! and histogram remains fairly normal ...Thanks Again Peter!


Dec 14, 2011 at 07:31 PM
Alan321
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p.1 #6 · p.1 #6 · Question Concerning change in Histogram


Image1, which camera have you got ?

Some cameras offer lossless compression of raw files, which works out faster than using uncompressed raw files because the extra time taken to do the compression is much less than the time saved by having to write less data to the memory card.


Any WB change to any image can push data (pixels) to the extremes of one or more colour channels. The less accurate the WB was at capture time the more significant some of those changes may be. Once pushed to near the extremes there is less tonal separation and some information may be lost. e.g. a bright red flower may take on the appearance of red blob with little or no texture in the petals.

A well exposed jpg of a not too contrasty scene with nearly correct WB can look very good, but muck those up and try to correct them and you could end up with information loss. Any 10-16-bit-per-channel format (not jpg) including raw may retain more of that info but eventually even they will be damaged if the errors were too great to begin with.

Using the tungsten setting for near-tungsten lighting is recommended by Canon, for example, in favour of auto WB. Auto WB works best at or near daylight and becomes less accurate at the higher and lower colour temperatures such as tungsten. Beware that if you shoot daylight scenes with the tungsten setting then everything will look very blue, so Auto WB may be the safest option.

- Alan



Dec 14, 2011 at 10:25 PM
cgardner
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p.1 #7 · p.1 #7 · Question Concerning change in Histogram


FWIW - The technical downside of tungsten lighting is the fact the camera records everything through red, green and blue filters and there isn't much energy in the blue region with tungsten sources relative to red and green. Due the the imbalance in the illuminant the camera must amplify the signal of the blue sites more than red and green resulting is much more noise in the blue channel and the image overall vs. one taken with a more balanced spectrum such as daylight or flash. Shooting JPG exacerbates the problem.




Dec 14, 2011 at 11:50 PM





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