What causes this banding in the sky?

Chazz5 · 10-22-2011, 01:14 PM

The sun is behind me. There was no hood on the lens, a Pentax-FA 35mm F2 AL.

I worry about the camera. Now the interesting part. What you see comes from the camera JPG in the PEF file. The banding shows up when Pentax Digital Camera Utility 4 opens the PEF, too.

However, when I open the PEF in Raw Therapee, a wonderful (and free) raw converter, there is no banding, even with the exposure raised to blow the blue channel and then enough to blow all three channels.

So I hope the K-5 has no serious problem, and I wonder why the Pentax JPG engine produces banding.

Thank you.

**Lowell Goudge** · 10-22-2011, 01:38 PM

This is from a near uniform sky and the loss if definition from 12 bit to 8 bit conversion. This usually happens when you boost contrast too far. The bands are 1 bit apart

Chazz5 · 10-22-2011, 01:45 PM

Thank you, Lowell. The default JPG shows the bands. I raised contrast a huge amount in Raw Therapee and saved a JPG. No banding. Maybe the camera and DCU code does all calculations in 8 bits, while RT does them in 16 bits per channel.

KevinR · 10-23-2011, 02:27 AM

That looks like a common effect caused by lossy compression. The compression tries to fine similar hues in the image that it can binned together in the compressed file. With the very subtle diferences in the sky color and intensity, this makes for perfect compression binning. But if the quality level is too low, the bin intervals present as distinct bands.

Try changing the JPG quality level, or short RAW+JPG to fix afterwards if banding occurs.

**Lowell Goudge** · 10-23-2011, 04:43 AM

Out of curiosity what was the jpeg quality

Chazz5 · 10-23-2011, 08:48 AM

I took the shot in PEF file format. The image in the original post was from the Fast Stone viewer opening the PEF. The Pentax DCU 4 preview shows banding, too.

The banding is in arcs, suggesting the lens has some role.

Just now I saved the image from Pentax DCU 4 six times: in 16-bit TIF and JPG at the 4, 3, 2, and 1-star compression levels, original size. Finally, JPG at 1-star level and both pixel dimensions cut in half. No banding on any of them! So the preview rendering algorithm is the culprit.

**paulh** · 10-23-2011, 08:59 AM

You will see this kind of banding when viewing certain photos on a pc monitor as well. It's not there when the display is set to 24-bit color, but dropping it down to 16-bit or lower will show the banding.

Last edited by paulh; 10-23-2011 at 09:05 AM.

KevinR · 10-23-2011, 09:40 AM

Originally posted by Chazz5

... So the preview rendering algorithm is the culprit.

AKA lossy compression on steroids...

Originally posted by Chazz5

...The banding is in arcs, suggesting the lens has some role....

Not related to lens in any way. Arcs follow color hue of the sky which I think is linked light passing through curviture of atmosphere. You sometimes get banding linked to color changes caused by vignetting in corners, but none here with the fine prime used.

Marc Sabatella · 10-23-2011, 09:57 AM

Originally posted by Chazz5

I took the shot in PEF file format. The image in the original post was from the Fast Stone viewer opening the PEF. The Pentax DCU 4 preview shows banding, too.

The banding is in arcs, suggesting the lens has some role.

Just now I saved the image from Pentax DCU 4 six times: in 16-bit TIF and JPG at the 4, 3, 2, and 1-star compression levels, original size. Finally, JPG at 1-star level and both pixel dimensions cut in half. No banding on any of them! So the preview rendering algorithm is the culprit.

???? If it shows the same in Fastone and DCU, it's not the rendering algorithm, unless both happen to have the same flaw. it's pretty clearly the preview itself. It's just a very low quality JPEG, prone to these and other artefacts.

Chazz5 · 10-23-2011, 10:49 AM

Originally posted by Marc Sabatella

If it shows the same in Fastone and DCU, it's not the rendering algorithm, unless both happen to have the same flaw. it's pretty clearly the preview itself. It's just a very low quality JPEG, prone to these and other artefacts.

You are right, my illogic. In fact, I just opened the PEF again in Pentax DCU4, went to the Laboratory tab, made a small change to the Sensitivity (Ev) and then moved it back to 0, no change. The banding in the Preview pane disappeared. DCU4 preview apparently starts with the camera JPG but shows its own preview as soon as the user has it do something on the PEF.

Am relieved there is no camera problem here. I came to the K-5 a few weeks ago after having electro-mechanical problems with two Sony A700's. Pentax +1, Sony -2.

mysticcowboy · 10-23-2011, 01:45 PM

Even high quality jpegs can display banding in some situations. A jpeg has 256 tonal levels. With very subtle shading between areas of a photo, you might see bands on prints of 8x10 or larger. Shooting in raw and editing in 16 bit mode brings that up into tens of thousands or levels. Theoretically a 16 bit image has over 56,000 levels. Since Pentax cameras work in 12 or 14 bit mode, the raw file won't have that many levels.

10-22-2011, 01:14 PM	#1
Chazz5 Junior Member Join Date: Sep 2011 Photos: Gallery \| Albums Posts: 40	What causes this banding in the sky? The sun is behind me. There was no hood on the lens, a Pentax-FA 35mm F2 AL. I worry about the camera. Now the interesting part. What you see comes from the camera JPG in the PEF file. The banding shows up when Pentax Digital Camera Utility 4 opens the PEF, too. However, when I open the PEF in Raw Therapee, a wonderful (and free) raw converter, there is no banding, even with the exposure raised to blow the blue channel and then enough to blow all three channels. So I hope the K-5 has no serious problem, and I wonder why the Pentax JPG engine produces banding. Thank you.

10-23-2011, 08:48 AM	#6
Chazz5 Junior Member Join Date: Sep 2011 Photos: Gallery \| Albums Posts: 40 Original Poster	Banding is in the preview rendering algorithm I took the shot in PEF file format. The image in the original post was from the Fast Stone viewer opening the PEF. The Pentax DCU 4 preview shows banding, too. The banding is in arcs, suggesting the lens has some role. Just now I saved the image from Pentax DCU 4 six times: in 16-bit TIF and JPG at the 4, 3, 2, and 1-star compression levels, original size. Finally, JPG at 1-star level and both pixel dimensions cut in half. No banding on any of them! So the preview rendering algorithm is the culprit.

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10-22-2011, 01:38 PM	#2
Lowell Goudge Site Supporter Join Date: Jan 2007 Location: Toronto Photos: Gallery \| Albums Posts: 17,892	This is from a near uniform sky and the loss if definition from 12 bit to 8 bit conversion. This usually happens when you boost contrast too far. The bands are 1 bit apart

10-22-2011, 01:45 PM	#3
Chazz5 Junior Member Join Date: Sep 2011 Photos: Gallery \| Albums Posts: 40 Original Poster	Thank you, Lowell. The default JPG shows the bands. I raised contrast a huge amount in Raw Therapee and saved a JPG. No banding. Maybe the camera and DCU code does all calculations in 8 bits, while RT does them in 16 bits per channel.

10-23-2011, 02:27 AM	#4
KevinR Veteran Member Join Date: Jan 2010 Location: Cape Town, South Africa Photos: Gallery \| Albums Posts: 653	That looks like a common effect caused by lossy compression. The compression tries to fine similar hues in the image that it can binned together in the compressed file. With the very subtle diferences in the sky color and intensity, this makes for perfect compression binning. But if the quality level is too low, the bin intervals present as distinct bands. Try changing the JPG quality level, or short RAW+JPG to fix afterwards if banding occurs.

10-23-2011, 04:43 AM	#5
Lowell Goudge Site Supporter Join Date: Jan 2007 Location: Toronto Photos: Gallery \| Albums Posts: 17,892	Out of curiosity what was the jpeg quality

10-23-2011, 08:59 AM	#7
paulh Site Supporter Join Date: Sep 2010 Location: DFW Texas/Ventura County, CA Photos: Gallery \| Albums Posts: 33,319	You will see this kind of banding when viewing certain photos on a pc monitor as well. It's not there when the display is set to 24-bit color, but dropping it down to 16-bit or lower will show the banding. Last edited by paulh; 10-23-2011 at 09:05 AM.

10-23-2011, 09:40 AM	#8
KevinR Veteran Member Join Date: Jan 2010 Location: Cape Town, South Africa Photos: Gallery \| Albums Posts: 653	Originally posted by Chazz5 ... So the preview rendering algorithm is the culprit. AKA lossy compression on steroids... Originally posted by Chazz5 ...The banding is in arcs, suggesting the lens has some role.... Not related to lens in any way. Arcs follow color hue of the sky which I think is linked light passing through curviture of atmosphere. You sometimes get banding linked to color changes caused by vignetting in corners, but none here with the fine prime used.

10-23-2011, 09:57 AM	#9
Marc Sabatella Veteran Member Join Date: Sep 2006 Location: Denver, CO Photos: Gallery Posts: 10,685	Originally posted by Chazz5 I took the shot in PEF file format. The image in the original post was from the Fast Stone viewer opening the PEF. The Pentax DCU 4 preview shows banding, too. The banding is in arcs, suggesting the lens has some role. Just now I saved the image from Pentax DCU 4 six times: in 16-bit TIF and JPG at the 4, 3, 2, and 1-star compression levels, original size. Finally, JPG at 1-star level and both pixel dimensions cut in half. No banding on any of them! So the preview rendering algorithm is the culprit. ???? If it shows the same in Fastone and DCU, it's not the rendering algorithm, unless both happen to have the same flaw. it's pretty clearly the preview itself. It's just a very low quality JPEG, prone to these and other artefacts.

10-23-2011, 10:49 AM	#10
Chazz5 Junior Member Join Date: Sep 2011 Photos: Gallery \| Albums Posts: 40 Original Poster	Originally posted by Marc Sabatella If it shows the same in Fastone and DCU, it's not the rendering algorithm, unless both happen to have the same flaw. it's pretty clearly the preview itself. It's just a very low quality JPEG, prone to these and other artefacts. You are right, my illogic. In fact, I just opened the PEF again in Pentax DCU4, went to the Laboratory tab, made a small change to the Sensitivity (Ev) and then moved it back to 0, no change. The banding in the Preview pane disappeared. DCU4 preview apparently starts with the camera JPG but shows its own preview as soon as the user has it do something on the PEF. Am relieved there is no camera problem here. I came to the K-5 a few weeks ago after having electro-mechanical problems with two Sony A700's. Pentax +1, Sony -2.

10-23-2011, 01:45 PM	#11
mysticcowboy Veteran Member Join Date: Apr 2009 Location: port townsend, wa Photos: Albums Posts: 968	Even high quality jpegs can display banding in some situations. A jpeg has 256 tonal levels. With very subtle shading between areas of a photo, you might see bands on prints of 8x10 or larger. Shooting in raw and editing in 16 bit mode brings that up into tens of thousands or levels. Theoretically a 16 bit image has over 56,000 levels. Since Pentax cameras work in 12 or 14 bit mode, the raw file won't have that many levels.