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pcr1040

Shadow like shading on left side of this hawk

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I shoot with a Sony a7R3 and the 100-400m m Sony GM lens.  While I am generally satisfied wit the lens performance, i noticed on some images I am getting a shading along the image as if it is out of focus or is astigmatic. I have attached one of these images reduced in size and cropped.  Please look at the left side of the Hawk's body and bring the image up insize on screen and you will see the shadow like area following the contour of the left side of the bird's body.  Any thoughts about his would be appreciated.

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I consider those "shades" to be artifacts from the (probably) jpeg-compression algorithm. This is a lossy compression algorithm, which is ...

Quote

A perceptual model based loosely on the human psychovisual system discards high-frequency information, i.e. sharp transitions in intensity, and color hue.  [highlight: mine]

Source: https://en.wikipedia.org/wiki/JPEG#JPEG_compression

Those "shadows" are also very pronounced at the left side of the almost vertical branch, right behind the bird's head. Note, that the most affected areas are indeed those with the "sharpest transition in intensity", like the highlighted portion in the above quote says.

I would expect, that those artifacts are not visible in a raw editor program, like Capture One, which allows you to view and edit the "raw", i.e. uncompressed image data.

 

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I thought I responded earlier to your thoughtful comment.  I guess I did not send it.  So let me  try to re state it here.  The image was a jpg, but, the I typically shoot only RAW,  and the unedited RAW image file has the same shadow on the left side of the Hawk, and it can be seen in some of the branches as well.  I am new to shooting wih the Sony System.  Formerly I shot wit a Panasonic G9 and a Panasonic lens 100-400mm lens.  I don't recall seeing such shadowing on similar shots of wildlife taken with the Panasonic system..

You also commented on the "sharpest transition in intensity"   I understand the comment, I think, but I would be interested in understanding how this could occur, and not be a astigmatic issue?  If you have a reference that explains it, I would be interested in seeing it.

Thanks for your help,

Paul  

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10 hours ago, pcr1040 said:

I would be interested in understanding how this could occur,

Well, you got me on that one. I'm not a mathematician myself, but you can't really follow along without some understanding of the mathematics involved. I'll try anyways:

Forget about the image for a moment, and just look at a scanline, or single row of pixels. You will see a pattern of intensity changes, depending on the nature of the subject which you were taking a picture of. Let's assume, you were taking a picture of a b&w checkerboard pattern. So your scanline could initially be represented by a square wave, alternating between zero intensity (i.e.: black) and maximum intensity (i.e.: white), and having sharp transitions between the two levels. So we're having lots of maximum intensity changes in our example.

The jpeg compression is intended to reduce the storage requirements, at an "acceptable" loss of information. The way it's done involves approximating the square wave (in our example) by a set of suitable sine-wave patterns of suitable intensities, and superimposing those different sine waves. The compression algorithm then basically only stores the amplitude values of the respective sine waves which were taken into consideration, instead of storing each pixel's intensity value. Taking ever more sine waves at ever increasing frequencies (and ever more miniscule amplitude values) into consideration, you can approximate the original square wave at arbitrary precision. The "lossy" part of jpeg compression comes from "cutting off", or discarding the highest frequency parts of that approximation.

See this image (and the surrounding article for further reference:

 

The "K" value in the above image represents the multiple of the square wave's frequency, which was taken into consideration. You can see quite nicely, how cranking up the K-value approximates those sharp transitions ever better. And likewise, how discarding the highest frequencies only approximates the initial sharp (vertical) transition with a more gradual "slope" like transition. Which is, what you perceive as a "shadow" in your example.

It also helps to know, that the jpeg compression involves a spatial downsampling into 8x8 (or even 16x16) blocks of pixels. Please consult my initial link to wikipedia on jpeg-compression for more information.

Hope that helps a bit.

 

Edited by Chrissie

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11 hours ago, LiveShots said:

What shutter speed for this image?

I am away from my iMac that has the original image, but my recollection is that the image was taken at somewhere above 1/1000 of a second and set on EFC.  Usually while walking in the field the camera is set on C2 (BIF) and the base shutter speed is 1/1500.  I seldom reduce it below 1/1000.

P

 

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2 hours ago, Chrissie said:

 

Hope that helps a bit.

 

Indeed it is helpful.  I will review the article referenced later today. I understand that jpeg compression is a lossy compression and can lead to artifacts like the kind I found in my image.  But keep in mind that the image had the issue, was a RAW image file, not jpeg.  I had to make a reduced size jpeg in order to send it to the Forum.   I am wondering if my lens has an issue that needs to be corrected?  Oddly enough, on most images, I seem to be fine with the level of sharpness I am getting with this lens.

 

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A couple of things to note...

At shutter speeds above 1/1000, EFC should be off. You can get odd image effects from having EFC on

Normal RAW images on Sony are not lossless. There is a bit of compression happening and there can be some weird things that happen in areas of extremely high contrast. Shooting in uncompressed RAW will fix that but result in larger file sizes.

https://www.google.com/url?sa=t&source=web&rct=j&url=https://phillipreeve.net/blog/limitations-of-the-electronic-shutter-function/&ved=2ahUKEwi8gou43azsAhVEheAKHVHuCzcQFjABegQIAxAB&usg=AOvVaw0zh_i89lDTxVvPcKWzbG2_

http://Can you see the Sony raw compression artifacts?

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Thanks for responding.  I never shoot compressed RAW.  All of my images are RAW and are full 80mgb. 

Thanks for the reference on the EFC shutter.  I am not sure it relates to the issue I have.  The shadow is on one side of the hawk and not top of the image.  

Paul

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A number of questions have been raised about the image I started this line of inquiry with.  Am I shooting Jpg or Raw?  Could the EFCS be the issue?  Could the issue be due to the contrast difference between the subject and background? and so on.  So let me add yet two image showing the same problem with different backgrounds. Please see the following images.  Notice the shadowing around the left side of the subject's head.  Originally shot in RAW converted in Affinity Photo to a jpg and cropped.  The raw image shows this "shadowing, just like the jpgs attached.  I also shoot with a different camera system, (m43)  and with a 100-400mm Panasonic lens.  I cannot find a similar issue on any of the images shot with the m43 system.   Is this common with the 100-400mm GM lens?  Or, as I am beginning to think, a defect in my lens?  Please note the third image close up of the bird.  No shadowing evident in this image taken with the m43 system with the lens at 400mm extension. 

Edited by pcr1040

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