Previous page Next page

JPEG Tone Curves / dynamic range

Our Dynamic Range measurement system involves shooting a calibrated Stouffer Step Wedge (13 stops total range) which is backlit using a daylight balanced lamp (98 CRI). A single shot of this produces a gray scale wedge from the camera's clipped white point down to black (example below). Each step of the scale is equivalent to 1/3 EV (a third of a stop), we select one step as 'middle gray' (defined as 50% luminance) and measure outwards to define the dynamic range. Hence there are 'two sides' to our results, the amount of shadow range (below middle gray) and the amount of highlight range (above middle gray).

To most people highlight range is the first thing they think about when talking about dynamic range, that is the amount of highlight detail above middle gray the camera can capture before it clips to white. Shadow range is more complicated; in our test the line on the graph stops as soon as the luminance value drops below our defined 'black point' (about 2% luminance) or the signal-to-noise ratio drops below a predefined value (where shadow detail would be swamped by noise), whichever comes first.

Note: this page features our new interactive dynamic range comparison widget. The wedges below the graph are created by our measurement system from the values read from the step wedge, the red lines indicate approximate shadow and highlight range (the dotted line indicating middle gray).

Cameras Compared

At default settings (Highlight Correction Off, 'Bright' Custom Image Mode) the K-30's tone curve is rather steep and more or less identical to previous Pentax models such as the K-01 or K-5. It measures a total dynamic range of approximately 8.5 EV, just 2.9 EV of which are in the highlights with a rather abrupt clip to white. This is slightly less than what we see from the K-30's direct competitors in the mid-level DSLR bracket of the market. However, additional dynamic range can be obtained by activating one or both of the K-30's dynamic range tools - Highlight Correction and Shadow Correction (see below).

Custom Image Modes

Like on the K-30 and K-5 the Bright, Natural, Portrait, Landscape, Vibrant, and BW settings use essentially the same curve and therefore produce the same amount of dynamic range. The Muted setting uses a more linear, less contrasty curve. Bleach Bypass and Reversal Film on the other hand create images with more contrast. However, all the settings clip highlights at the same point. Cross Processing (which was previously available as a filter) has now moved into the Custom Image menu and has a very contrasty tone curve.

Dynamic Range Expansion

You can expand the dynamic range in your images by activating one or both of the K-30's dynamic range tools - Highlight Correction and Shadow Correction. These features exemplify the two different methods widely used by cameras to improve the dynamic range conveyed in the final image.

Technically, Highlight Correction is like underexposing by a stop to avoid blowing highlight detail, and then pulling up the midtones and shadows in post-processing to compensate, giving an image of the correct overall brightness. This results in an increase in the camera's lowest-available ISO to 200 when Highlight Correction is turned on.

Shadow Correction is a much simpler concept in that it simply boosts the brightness of shadow regions to create a more balanced image. The level of shadow correction is user definable in four steps (Off to 3). There's also an Auto setting in which the camera applies one of these four settings, depending on the contrast in the scene. None of these options increase the Dynamic Range, per se, but can pull detail out of deep shadows so that it's visible in the final image.

Shadow and Highlight Correction apply to both JPEG and Raw images. A Raw converter that fully supports the K-30 should recognise the need to use a different tone curve to process the result. At worst, with Highlight Correction switched on a non-mainstream converter you might have a shot that initially looks underexposed and needs 1EV of extra exposure applied.

You can also combine Highlight Correction with any level of Shadow correction which gives you quite a few possible combinations to play with. In the widget above we have included the tone curve for Highlight Correction On and Shadow Correction High. As you can see the image has both - more detail in the highlight areas and slightly lifted shadows although the effect at both ends of the spectrum is not as pronounced

Previous page Next page
148
I own it
32
I want it
20
I had it
Discuss in the forums

Comments

Total comments: 7
adrianconst

When I compare the dynamic range of K30 against D7000 and T5i, it looks like K30 under performs. However, that might be because the K30 default contrast in all modes is pretty high compared to the other two. Maybe dpreview should mention that when it presents dynamic range results.

0 upvotes
oldnoob

In the RAW Standard studio scene comparison, the k-30 appears to be back-focusing a bit. look at the small writing on the Kodak grey scale

0 upvotes
JustSomeOldDude

And the "Q" on the queen card is sharper than anything

0 upvotes
ebaker

I called the corporate office myself and spoke with Joe Virgil, who was apologetic, but insisted he couldn’t do anything because the part was being shipped from the Phillipines and there were 65 other service orders suffering from the same problem. I explained that his supply problem was now a customer service problem as we had reached the 7th week of this ordeal. After ordering a part, if it has not arrived in 5 weeks, they are supposed to provide a replacement and this has yet to happen.
When you purchase a camera, you also purchase warranty and customer service with it. This has now past over two months since I initially sent off my camera for repair and the company is refusing to honor its warranty. I have bought a DSLR from one of their competitors and am completely disgusted with Pentax — DO NOT GIVE THEM YOUR BUSINESS. I’ve yet to receive my camera back (10 weeks and counting!) or any kind of a firm timeline of when that might happen.

1 upvote
A1200

Hi ebaker,

Did you get the repaired camera from them?

0 upvotes
ebaker

I actually liked the camera…. until it didn’t perform as promised. I bought this camera because I work at an aquarium and need to take photos for our marketing. A month after purchase, the telephoto lens drew humidity into the body and condensation formed, thus killing the LCD screen.
While it claims to be weather resistant, it couldn’t even handle humidity.
What is worse is that after sending the camera in on July 6 for repair under the warranty, I have yet to get any kind of a realistic timeline of when I would receive my camera back. After the fifth week of hearing, “Call back next week” I requested a replacement. This caused the customer service rep to become extremely rude and tell me that they were in the midst of a corporate merger so he couldn’t help me. I requested to speak with a manager, he refused to give me their name or number. He insisted he needed to call the corporate office and said he would call me back by the end of the week. Of course, that never happened.

1 upvote
Take5

“…the only major barrier to fast and efficient operation is the relegation of movie shooting to the exposure mode dial.” Seriously is the time difference between turning the mode dial and pressing a button to enter the movie function all that relevant – you are talking about an extra second at the most !

0 upvotes
Total comments: 7