Solve unwanted white "waves" and "Pacman squares" in low-light picture - post using Google Photos

Question

After op commented that my picture is super under-exposed, I tried post using Google Photos. But when I increased the exposure, I saw some unwanted white "waves" or rows in the photo. The edges of these rows, when you zoom in closely, looks like "Pacman squares". Original picture is shot through f/8, 30secs, ISO 200, ec -1. Shot through Fujifilm X-T100 mirrorless camera with focal length 15-45 mm, max aperture of 3.61, pattern metering mode. What can I do during the shoot and during post to solve these? I just started photography less than a week ago, and would like to learn as much as possible. Thank you ! :)

OP comment is from this thread: How do I take a photo so the moon doesn't have bright "rays"?

OP is short for "original poster" and on this site normally refers to the person that asked the question (you). Good question - keep em coming! — JPhi1618, Dec 13 '19 at 21:25

score 19 · Accepted Answer · answered Dec 12 '19 at 17:40

19

This is known as "banding". Dark parts in the picture have a small range of values (in a JPG, you only have 256 values per color), when you lighten them, you increase the gap between consecutive values as much as the values themselves. Since the gaps more or less follow a line they are very noticeable by our eyes.

Several fixes are possible :

If you have the raw file, work on the raw file (more bit depth, no gamma correction)
On the JPEG alone you can fix the problem by applying "spread noise" (which is really swapping pixels randomly with close neighbours) which makes the lines disappear (use a suitable selection):

answered Dec 12 '19 at 17:40

xenoid

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Also known as 'posterization'. – Lamar Latrell Dec 14 '19 at 07:42
Posterization is a reduction of the number of colors. This is not what happens here. – xenoid Dec 14 '19 at 09:25
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I can only refer you to your own answer in rebuttal ¯\(ツ)/¯ – Lamar Latrell Dec 14 '19 at 21:09

Romeo Ninov · Answer 2 · 2019-12-12T17:54:02.797

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This is named banding. And it's caused in your case by overprocessing the image. What you can do is to take the photo in RAW and postprocess it. When postprocessing mask the sky and do not increase the exposure there. At the end night sky is dark.

You can also take two photos, one as it is and one for the buildings. And mix them keeping sky dark and buildings light.

edited Dec 12 '19 at 17:54

answered Dec 12 '19 at 17:25

Romeo Ninov

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It's not necessarily over processing. Could be from high JPG compression. – xiota Dec 12 '19 at 19:57
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@xiota, right. IMHO this compression also can be named processing :) – Romeo Ninov Dec 12 '19 at 19:58

score 1 · Answer 3 · answered Dec 12 '19 at 20:36

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Even if you processed the raw files initially, when you upload them to sites such as google photos, they may compress them further to reduce the bandwidth needed to transmit them to viewers. This compression can also cause banding.

answered Dec 12 '19 at 20:36

Michael C

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Solve unwanted white "waves" and "Pacman squares" in low-light picture - post using Google Photos

3 Answers3