What are these artefacts?
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Old 07-28-2014   #1
Vicuna
 
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Default What are these artefacts?

This picture was taken with Canon Powershot SX 260 HS at full zoom (Focal Length 90mm = 450 mm 35mm Eq) saved on an SDHC Class 10 card.

Can anyone throw some light on the artefacts seen in the 100% crop? These have been regularly seen in every picture, much more prominent when a class 4 card was being used.

Also please indicate a remedy if at all possible.

1. Picture unaltered in size. An auto levels adjustment was done in GIMP.



2. 100% crop:



Thanks in advance.

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Old 07-30-2014   #2
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Default Re: What are these artefacts?

Can't see any EXIF data. There is quite a bit of noise at 100% crop. May be due to high ISO or increasing the brightness in post-processing. In-camera sharpening, if set at a high level, can also produce noise. I use SX50 & at ISO above 400, noise becomes evident.
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Old 07-30-2014   #3
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Default Re: What are these artefacts?

Gautam, thanks for the reply.

Could it be due to JPEG compression? Unfortunately, this model doesn't offer RAW or TIFF formats.

They were much more prominent & more often seen in another card that I was using earlier. It was a class 4 SDHC card, whereas the present one on which this pic was taken is a class 10 SDHC card.

Here is the EXIF Data:
Attached Images
File Type: png Screenshot2.png (30.8 KB, 104 views)
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Old 07-30-2014   #4
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Default Re: What are these artefacts?

The ISO was not high so the probable culprit is jpeg compression. You can use a noise reduction software to clear it up a bit. Noiseware has a free (community) version, you can try that out. This is what I got after running it through Noiseware at default settings. I hope you don't mind me editing your picture.

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Old 07-30-2014   #5
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Default Re: What are these artefacts?

does it look similar when you haven't zoomed all the way out? i remember having an old kodak p&s with a ton of zoom that had very soft and speckled look to it when zoomed out to max. it seemed like the camera was sharpening after a certain focal length to make up for shoddy optics.
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Old 08-02-2014   #6
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Default Re: What are these artefacts?

@Gautam

I know noise can be reduced by using noise reduction software & I use Neat Image for noise reduction. But I wanted to know what are these artefacts due to in the first place so that I can avoid if there is an avoidable cause. They are also getting reduced by despeckling in PS.

@ rocket

I will observe if they are more when zoomed out fully.

Sharpening can be adjusted both ways (up & down from default setting) by the user in several steps in this camera. I have reduced the sharpening but there was no influence. Now, I have increased the sharpening to the max & I will observe over the next few days.

Thanks both of u for your valuable time.
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Old 08-02-2014   #7
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Default Re: What are these artefacts?

These are 3 of the "cons" mentioned in a review of your camera by dpreview:
  • Critical image quality somewhat lacking at 100%
  • Some highlight clipping and purple fringing (try using i-Contrast to reduce the former)
  • Autofocus performance lags behind the competition; camera struggled to focus in low light at times
So, the jpeg artefacts may well be caused by in-camera processing.

Obviously Gautam's simple treatment improved your 100% image no end. I suggest you follow in his footsteps or try the Topaz DeJPEG plugin.

Martin
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Old 08-02-2014   #8
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Default Re: What are these artefacts?

Thank u Martin.
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Old 08-02-2014   #9
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Default Re: What are these artefacts?

Quote:
Originally Posted by ssreddy555 View Post
Thank u Martin.
BTW, I have a Powershot G12 with a sensor of similar small size to the one in your Powershot SX 260 H. I get some noise (easily removed) even at ISO 200.

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Old 08-02-2014   #10
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Default Re: What are these artefacts?

Caution....Viewing at a 100% crop is not a good idea. You are magnifying the pixels to such a degree that it is an unrealistic view. In this case, it makes sense because you are concerned about noise, but don't do it on a regular basis. You will drive yourself crazy.

Are you planning to print your photos or to view them on screen only?

Since you are restricted to jpg, your first step should be to perfect your in camera settings and your shooting method to produce the best possible jpg you can. Try as much as possible to shoot the end product you want. Strive to achieve good composition, exposure, sharpness, white balance, etc.

What in camera settings did you use...not your exposure settings, but your sharpness, contrast, shooting mode if you used one (vivid, portrait, etc.)?

Did you use digital zoom or optical zoom only? Highlight setting on or off?

You said you used auto levels? Was your photo over or under exposed?

I know I'm asking a lot of questions, but some of these factors may be contributing to the problem.


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