BrianO Offline Upload & Sell: Off
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Bsmooth wrote:
Ever since everything went digital, especially television, I've noticed a certain "blockiness" to shadow and dark areas of the images. ...Is it lack of dynamic range that causes it or is it the sensor itself?
Yes.
And no. DR is a parameter of the sensor/amplifier, and some sensors have more DR than others.
However, noise from amplifying low light levels usually appears as scattered speckles of colored pixels, not as "blockiness."
Blockiness, also known as pixelation, is -- as mentioned above -- more often an artifact of image compression. The JPEG format doesn't record/transmit all the pixel information in a scene, but to save space/time will send information on large sections of equal -- or nearly equal -- tone as if it were a single larger pixel. Also, instead of saving, for example, thousands of shades of blue, it might save a gradient of all those blues as "bands" of only a few hundred different tones...or even fewer.
You can test this yourself if you have image-editing software by taking a sample image and doing several "Save as..." operations in .jpeg format, each one at ever smaller file sizes. The smaller the file, the more pixelated it will appear.
For example, here are two resized and saved versions of a picture I took several years ago. The first one has a 453kb file size (minimal compression) and the second one is only 48.5kb (maximum compression).
Yes, the DR exceeded that which my camera could capture (it was more than 12 stops' difference), so I exposed for the most important parts and let the whites and blacks clip, but in the larger file the range of tones that did record is more-continuous, as shown in the third image.
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