What is *clipping*?

I'm not sure if this is the right forum or the right category. But

I've come across the term *clipping*, usually related to clipping

whites or clipping blacks in images.

 

What does the term mean and is it something to avoid? If so, why?

Any examples of good or bad clipping someone can point me to?

 

Thanks.

If you're clipping highlights or shadows, the sensor isn't recording any detail in that area.

 

Clipped highlights would be an area that was recorded as pure white (RGB values of 255,255,255) even though there were details visible. Doesn't necessarily have to be pure white, but bright enough so that detail is lost.

 

Clipping shadows would be the same thing, but with dark values in the scene.

If you have PS, open a picture, open up a Levels dialogue box, and then hold down on Alt as you drag the white (right) or black (left) slider in towards the center.

 

The colors that come up show clipping - so you might clip the blue channel information from a guy's t-shirt, and then it will go to solid white, meaning that if you leave it that way, and print it, it will be pure white, without any texture or color at all.

 

It's okay to clip reflections of the sun on the water, or streetlights and so on, but nothing where you want details, like a white stallion's fur.

 

With the blacks, everything goes to black - so there's no detail in the shadows. So with a black horse, you wouldn't see the fur.

 

It's often best to adjust Levels to just inside the clipping areas, so you have a full range of tones from black to white.

 

I've been reading Katrin Eismann's "Restoration and Retouching," which covers all this well, as will many books on PS. It really is necessary to know it to get the best out of your pictures, and Levels (or Curves, for the experienced) is the tool to use instead of Brightness/Contrast.

In pure technical terms, clipping is the input level is higher than the maximum input level of the analog to digital conversion. Say your A/D converter would record it's maximum value, say, 256 when you input 1 Volt and you put in 1.5V, the value recorded is still 256. That is clipping.

 

If you clip, or over expose, all the levels above the maximum will be pure white, so that is something to avoid. But sometimes, just like with film, you don't have a choice and you need to either under expose the shaddow areas or over expose (clip) the highlights because the dynamic range in the scene is too great for your sensor to record.

 

Trick around it are shooting two frames, one for shaddow detail, one for highlights (tripod required!) and the good old neutral density gradient filter, which is darker at the top; the landscapers tool for keeping skies in check.

Graphically, visualize a sine wave with horonzontal lines that chop off the top and bottom curves, effectively flattening them.

 

Not a good thing to see, or hear.

Clipping: Forces pixels to pure white (level 255) or pure black (level 0).When working with

digital images, the highlight and shadow values are a fixed scale. In the case of an 8-bit

file, level 255 represents the whitest white and level 0 represents the blackest black. If a

user had a full tone image over this scale but set Photoshop to move all values from 250

to 255, values 251 through 254 would be clipped to white. All the tones that show the

subtle differences from 251 to 254 would all be clipped to pure white (255). Clipping is

the result of taking tones and mapping them to the extreme end of the tone scale.

<p>Note that clipping doesn't just happen with white or with black. There are three colours recorded (red, green, blue), and there are cases where one or two colours are clipped but the other isn't. This causes some of the colours to shift. For instance, imagine something with an RGB value of (225,200,100), which is sort of orange. Now overexpose it a stop. It should become (450,400,200), which would be a brighter orange, but in eight bits, the maximum value for each is 255, so you end up with (255,255,200), which is yellow. The colour shifted because of clipping.</p>

<p>Grr ... time for this software to move forward into the 1990s and start supporting PNG files. Here's the same thing as a GIF.</p>

Thanks folks.