Monday, May 9, 2011

Get it "Right" With Your Histogram



Here's a guest post by my friend, and DPE podcast co-host, Juan Pons

Good advice, Juan. Thank you for sharing. I just love your bison in the mist shot!
 
“Expose to the right” is an expression that you may have heard before, but my experience has been that most folks don’t understand what it means or how how to do it.

In simple terms what this means is that in order for you get the absolute best image quality your digital camera sensor can produce you should be slightly over-exposing your images. I know this does not sound like good advice, but bear with me for a minute, there is a very good technical reason for this.

The imaging sensor in your digital camera is composed of millions of little light sensors (as many as your camera has Mega pixels), and each of these sensors measures the intensity of the light that falls upon it, the camera then takes these millions of measuring points to create an image. However these sensors are not equally as good as measuring light at all levels, actually they are magnitudes more sensitive near the highlights than they are near the dark areas.
 ExposeToTheRight

What this means is that your camera can record much more detail in the brighter parts of your image than the darker parts. Therefore to get the best image quality from your camera you need to slightly over-expose your images or “shoot to the right” in order to fully take advantage of your sensors capabilities.

The tricky part here is not to over-expose too much so as to “blow out” your highlights, because if you go too far you will lose all the detail in those blown out areas. How do you know how much to over-expose? This is where your camera histogram comes in handy. Your cameras histogram simply displays to you how much information has been recorded at each light level, from dark (left) to light (right). A normally exposed image will have a histogram that shows most of the information bunched up in the middle.

Exposing to the right means just that, to expose your image such that the histogram shows the majority of the data bunched up on the right side of the histogram as opposed to right smack in the middle.

HOWEVER, you need to take care not to let that data “bump” up against the right edge, because that data will be lost; this is where those over exposed flashing alerts that are part of most cameras preview screens come in handy. Yes, sometimes you will want pure white, blown out areas in your image, and that is ok, just use your judgement here.


When you look at these RAW files (this will only work when shooting RAW ) in your favorite image processing software, the images will most likely appear a bit over exposed, but that is ok, as you can easily adjust the exposure to make the image look “right”.

7 comments:

Orcatek Photography said...

I've been telling my photography students this for a long time. I will be referring them to this post as you did a good job talking about the topic and why I keep telling them to expose to the right.

sydjeii said...

why is it that when i look at the monitor of my camera, the histogram (i mean the curve)is centered..but when i import photos in photoshop lightroom, the graph is moved to the left.. sorry im a photography newbie.. :)

Iain said...

I have also been teaching this for a long time, but some folks do not accept it. Good post Rick and I will also point my students in this direction

sbrener said...

Just curious. How far to the right would you go with an image that is very dark, and would normally bunch up on the left side?

sbrener said...

Just how far right would you go with a very dark image that would normally skew very far to the left? Thanks.

Outdoor Guy said...

The last book I read said I should do the opposite.

Time to go hiking and see which tip makes more sense.

Francie said...

This is the best explanation on the subject that I have read, thanks so much, NOW it makes sense!