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What exactly does it mean to "crush the blacks"?


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#1 Seth Mondragon

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Posted 08 June 2006 - 02:24 PM

just what the title says....What exactly does it mean to "crush the blacks"? I hear this all the time but never really known what it means. Thanks.
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#2 Stephen Williams

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Posted 08 June 2006 - 02:55 PM

just what the title says....What exactly does it mean to "crush the blacks"? I hear this all the time but never really known what it means. Thanks.


Hi,

Turning dark areas that are not black to black. In doing so, detail is lost and can not be recovered. I have seen people light very flat, then crush the blacks to make some contrast. Lighting with more contrast is better IMHO

Stephen
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#3 David Sweetman

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Posted 08 June 2006 - 03:15 PM

It's something that happens in post along with the color correction.

Basically, it "crushes" any light in the shadow areas, rendering them instead as black.

One reason you'd do this is for a horror flick, where you want little detail in the shadow areas so the audience may be led to think there's something "lurking" there.
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#4 Seth Mondragon

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Posted 08 June 2006 - 03:23 PM

Thanks for your reply....is this a good example of crushing the blacks?
Posted Image
Posted Image
I basically just increased the contrast a bit, but I'm sure there's more to it when dealing with telecine and other post work. But I just wanted to see if I have the right idea. Thanks for your help.
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#5 Josh Bass

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Posted 08 June 2006 - 03:35 PM

Are they only referred to as crushed when they go completely black? What if you just darken the shadow areas without killing all detail?
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#6 Michael Collier

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Posted 08 June 2006 - 04:10 PM

Are they only referred to as crushed when they go completely black? What if you just darken the shadow areas without killing all detail?



Then your talking about contrast. Contrast will push anything over 50ire up and below 50ire down. It helps if you have spent anytime staring at a waveform monitor. You will notice when you apply contrast, its almost as though both sides are grabbed and either streched or compressed. Crushing the black would only affect the shadow areas. You would see the low end of the waveform being pushed down even further, while the highlights and midtones stay relatively in place.

If you just darken shadows but leave detail, it still could be considered crushing the black, but only if the shadow is the only affected area. Adding contrast adds it equally to all portions of the image.
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#7 Michael Nash

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Posted 08 June 2006 - 04:17 PM

Are they only referred to as crushed when they go completely black? What if you just darken the shadow areas without killing all detail?


Then that would be "darkened," not crushed. "Crushed" usually means that some detail is lost, lowered to the point of being black. But the more you "crush," the more dark areas above black also become "darkened."

Crushed black:
BlackCrush_3.jpg

"Crushed" black is the opposite of "clipped" white (in terms of luminance). "Clipped" means that bright input values are made higher than the brightest output value.

Clipped white:
clipped_whites.jpg
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#8 Seth Mondragon

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Posted 08 June 2006 - 05:01 PM

okay, cool. that explains it a bit better for me. and also thanks for using my photos to show an example (i'm a visual learner).

Thanks again!
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#9 Alessandro Machi

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Posted 09 June 2006 - 02:25 AM

It helps if you have spent anytime staring at a waveform monitor. You will notice when you apply contrast, its almost as though both sides are grabbed and either stretched or compressed.


Sad to say, people don't seem to realize how inexpensively older working waveforms can be bought for.

I've had a waveform and a separate vectorscope staring at me from between my two professional television monitors for the past 10 years.
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#10 Tony Marsden

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Posted 12 July 2006 - 05:56 AM

Strictly speaking, there IS a difference between 'crushing' and 'clipping'

'clipping' implies that some highlight or lowlight information has been lost for ever; in digital terms, this is as if all values over a certain amount (say) were limited to 255; in photograhpic terms, we talk about 'blown' highlights. The same applies in the opposite sense to lowlights.

'crushing' on the other hand can imply that certain values approaching white (or black) will be compressed into a smaller output range than the input range; the implication being that some detail MAY be retained, albeit lost in the darkness / lightness.

This is more akin to the chemical process in silver-halide photography, where the position of the image dynamic (tonal) range on the film's slope will determine to what extent lowlights, highlights, or both may be compressed by falling on the 'toe' of the curve.

In a video situation, it is much more of an all-or-nothing hard clip.

Thankfully, these days, electronics and software offer us impressive possibilities for the createive management of tone curves etc.
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#11 Tony Marsden

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Posted 12 July 2006 - 06:25 AM

If this attachment has worked, here's a quick image file that I've cheated in Photoshop to simulate the 2 effects.

The centre image is the original, unprocessed.

The top image has had both whites and blacks clipped; the accompanying histogram shows the black and white cut-off or clip points --- anything above or below those limits is 'thrown away' and will not be reproduced in the final 'clipped' image.

The bottom image has had both whites and blacks crushed; the tone curve to the right shows that all the original input image dynamic range still exists (no information is 'lost') in the output image, but that the mid-range contrast has been increased slightly, at the expense of crushing in high- and low-lights.


crushing_clipping.jpg 2nd try for that attachment!
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#12 G McMahon

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Posted 12 July 2006 - 10:38 AM

The bottom image has had both whites and blacks crushed; the tone curve to the right shows that all the original input image dynamic range still exists (no information is 'lost') in the output image, but that the mid-range contrast has been increased slightly, at the expense of crushing in high- and low-lights.
crushing_clipping.jpg 2nd try for that attachment!
[/quote]

Isn't what your done just effectively is increased the contrast (in the bottom picture), since you have increased the gradient of the exposure curve?

I have attached a diagram of what I believe changes to pictures would do to the exposure curves. I am not confident that these are correct. I am also not sure of how the "x" and "y" axis would be labeled. Could someone elaborate.

Am I right in assuming that a higher contrast stock has lower latitude than a lower contrast stock?

Thanks all,

Graeme

Attached Images

  • curves.jpg

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#13 Alessandro Machi

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Posted 12 July 2006 - 11:24 AM

Am I right in assuming that a higher contrast stock has lower latitude than a lower contrast stock?

Thanks all,

Graeme


That sounds right. However if you are shooting under very flat lighting conditions, I might prefer the higher contrast stock.
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#14 Chris Keth

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Posted 12 July 2006 - 11:30 AM

just what the title says....What exactly does it mean to "crush the blacks"? I hear this all the time but never really known what it means. Thanks.



It's what you do when you go into Photoshop and move the black point higher then some of the information on the histogram. If you simply want to darken the blacks, you don't move the black point past any information.
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