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FORUMS Canon Cameras, Lenses & Accessories Canon EOS Digital Cameras 
Thread started 07 Mar 2010 (Sunday) 08:48
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Questions re. Highlight Alert

 
Scott_online
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Mar 07, 2010 08:48 |  #1

Aka the 'blinkies'.

I frequently use these to judge how much exposure compensation I need to dial-in in order to minimise blown highlights on a subject (i.e. I dial-in negative compensation until I can get rid of the blinkies, at least in the section of the image that I'm bothered about).

However, I've noticed that when I actually get the RAW into DPP, I can usually undo whatever compensation I've applied without triggering DPP's highlight alert.

I'm shooting RAW only, but I think the camera still generates a JPEG for display purposes and to embed in the RAW. Is this correct? If so, is the camera's histogram based on the JPEG or the RAW? That might explain why the camera thinks the highlights are clipped when in fact they're not.

:confused:


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pingflood
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Mar 07, 2010 08:58 |  #2

Yes, you are absolutely correct; the JPEG is embedded and based on the camera settings; histogram is generated from that. If you lower the contrast on the camera settings you can usually get it closer to the "real" limits of the RAW though you'll still be able to recover some of the "blinkie" areas.


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bohdank
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Mar 07, 2010 09:13 |  #3

It's based on the JPG, hence the Picture Style. Other than Faithful/Nuetral, the other ones are all jacked in one way or another. If you are using the blinkies (I do) then set the camera to either of the 2 PS's I mentioned. I use Faithfull.

It's best to get it right, in camera, since there is only so much you can do in post. If any one channel is truly blown out, beyond recovery, you can still eliminate the Highlight Alert in post but if the color information is truly lost (255), all you will be doing is removing the alert but not recovering the color information since none is there.


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pingflood
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Mar 07, 2010 09:14 |  #4

bohdank wrote in post #9745421 (external link)
It's based on the JPG, hence the Picture Style. Other than Faithful/Nuetral, the other ones are all jacked in one way or another. If you are using the blinkies (I do) then set the camera to either of the 2 PS's I mentioned. I use Faithfull.

It's best to get it right, in camera, since there is only so much you can do in post. If any one channel is truly blown out, beyond recovery, you can still eliminate the Highlight Alert in post but if the color information is truly lost (255), all you will be doing is removing the alert but not recovering the color information since none is there.

If you're looking to get the best possible raw image to work with, getting it "right, in camera" means pushing the boundaries a bit and having highlight alerts regardless of your jpeg settings. You're right that once it's blown it's blown, but there's a fair bit of headroom that you're missing out on if you shooting strictly within the jpeg parameters.


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Scott_online
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Mar 07, 2010 09:21 |  #5

Thank you both.

I guess the trick is knowing just how much you can push it...


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bohdank
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Mar 07, 2010 10:14 |  #6

pingflood wrote in post #9745426 (external link)
If you're looking to get the best possible raw image to work with, getting it "right, in camera" means pushing the boundaries a bit and having highlight alerts regardless of your jpeg settings. You're right that once it's blown it's blown, but there's a fair bit of headroom that you're missing out on if you shooting strictly within the jpeg parameters.

Very true. I did not say that one must eliminate all blinkies incamera nor is it necessarily something you would want to do, depending on the shot and lighting but, with experience, one gets better at judging what is more important.

The more accurate your starting point (Faithful/Nuetral) , the better position one is in making an informed decision.


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RDKirk
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Mar 07, 2010 10:27 |  #7

Scott_online wrote in post #9745451 (external link)
Thank you both.

I guess the trick is knowing just how much you can push it...

A bit of testing will tell you that.

Compare this in your testing as well with your camera set for the RBG histogram, rather than just the luminance histogram (the blinkies work with luminance, BTW). The RGB histogram will show you how and where some highlights blow out the predominant channel before blowing then all out--the luminance histogram (and the blinkies) only show you when all three channels are blown.

This is why skin highlights frequently go out of control. The red channel in skin tones blows out first before the blinkies make note of it, and you wind up with bald highlights when you know you should have had more headroom in raw than you saw on the luminance histogram or the blinkies. But if you close tight to, say, the forehead of the subject, the RGB histogram would show you that the red channel was clipping.

Now, you don't always (and can't always) zoom in on the subject's forehead to do an RGB histogram reading, but if you do some careful testing, you can determine how much "Kentucky windage" to give exposure in the common situations that you run in to.

One good thing about the old Zone System...at least you learned how to really test the capabilities of your tools, processes, and materials in a systematic manner.




  
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tzalman
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Mar 07, 2010 10:43 |  #8

If I see blinkies I look at the green histogram. The sensor is more sensitive to green so in most lighting the green channel receives more exposure. (The exceptions are filtered light sources, like in a rock concert or a close-up of a rose where all the light entering the lens is reflected from the flower.) During the white balancing done to the embedded jpg the red and blue values are multiplied to bring them up to and beyond the green and this can trip the blinkies, but the green channel remains very close to its RAW level and in most situations if the green is not clipped the other two channels are not either.


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MGH
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Mar 07, 2010 11:05 |  #9

Hi...If you always shoot RAW and you can live with a green cast to the camara display then use UniWB and a Nuetrel picture style.I have a Canon 500D and it works perfect.If you do not know what UniWB is There´s lots of info in this forum,do a search....


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Erik_L
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Mar 07, 2010 11:32 |  #10

some good info in here. I just turned my blinkies on and switched to RGB histogram - was never sure of the benefit before reading this. This is especially useful when trying to get shots of my friend welding -

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IMAGE IS A REDIRECT OR MISSING!
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I over-exposed because most of the arc is "blown"

then again, it would look pretty stupid if you could see the wire hitting the metal - the illusion of "IMMENSE FLAME" would sortof be destroyed.

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Questions re. Highlight Alert
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