What Causes This Blowout?

[norfolk_nsfw_maybee]

<p>My brother sent me a pic taken with his new camera, and I noticed the blowout (I am sorry, I do not know the correct term for it) if front of the rear tire.<br>

<img src="http://i1104.photobucket.com/albums/h332/sweetmk22/48Olds.jpg" alt="" width="800" height="681" /></p>

<p>What causes this? </p>

<p>Thanks for the help.</p>

[ann_overland]

<p>This is not a blown highlight problem.</p>

<p>Is this a jpeg file straight from the camera? Or has he done any postprocessing to the file? If so, was it a RAW file or a jpeg file? And what software did he use to process the file?</p>

[drjoder]

<p>Maybe you could also clarify exactly what you mean by "blowout" as "blown highlight" doesn't seem to match what you are talking about. "Blocked shadows" maybe...???</p>

[norfolk_nsfw_maybee]

<p>The area between the chrome gravel guard and the door, shaped like a large oven mitten shows it most predominantly.<br>

Actually it is on the entire door. <br>

The defect is not in the original photograph, just the downsized version. I had him send the original "out of the camera" jpg. That jpg looks OK.<br>

So, whatever he is doing to reduce the file size with his MAC computer is invoking the problem.<br>

Any ideas?</p>

[rnt]

<p>Ah... He's downsizing by reducing the image quality, not by (or just by) actually reducing the image size. With lower quality JPG's you'll get those artifacts in areas where there's a tonality gradient- the door, a clear sky, etc.</p>

[ann_overland]

<p>The image is only 47KB. But the original file size must have been bigger than 800px x 681px.</p>

<p>Can you attach the original jpeg for us to look at, John?</p>

<p>What software did he use?</p>

[norfolk_nsfw_maybee]

<p>I reduced one of his pics using Photo Gallery on my PC.<br>

<img src="http://i1104.photobucket.com/albums/h332/sweetmk22/IMG_0145800x685.jpg" alt="" width="800" height="685" /><br>

I do not see the problem in this pic. I will try to find out the method of pic file size reduction he used.</p>

 

[Matt Laur]

<p>Yup, just JPG compression artifacts. Trying to make the file too small (in bytes) causes subtle tone changes to disappear into blocks of single hues/tones. Less compression makes for more detail and better tonal gradiations, but larger files. There is no single sweet spot - it's something you sometimes have to fine tune per image, based on the content and just how small you want that file to get.</p>

[mendel_leisk]

<p>I <em>think</em> his concern is "blocking up", ie: the near solid-dark zone ahead of the rear tire, and just struggling with the terminology.</p>

<p>Off topic, the tire doesn't look at all flat: definitely not a blow out ;)</p>

[dave_redmann]

<p>Looks to me pretty clearly like banding / posterization due to excessive compression. It is a relatively common type of the JPEG compression artifacts that Matt mentions. Actually, it is more common in excessive video compression--on my cable TV, the channels that get less bandwidth often show it, especially in darker areas of the image.</p>

<p>The open-source (free) digital photo editing program GIMP is a great way to experiment with / learn about this. You can save an image as a JPEG with very different compression settings, resulting in quite different final image quality.</p>

[Mark Keefer]

<p>I agree, over compression of the file (making the file as small as possible at the expense of sacrificing picture information)<br>

The first photo almost looks like it was compressed to GIF format (only 256 colors)<br>

To prevent this or minimize it, always select save with highest quality as a JPEG in the settings.</p>

[gregoryl]

<p>Yes, over compressed jpeg which leads to posterization. Instead of a smooth graduation of tones they become abrupt and blotchy. </p>