tainkc Loc: Kansas City

Well, I do know the actual cause-compression. But the reason I am so puzzled is that I saved it at little over a 1/2 meg (674k to be exact.

I had to go up to 1.7 megs to get rid of the banding. This seems a little big. Blue backgrounds shows this banding best for some odd reason even though I have seen it with other colors.

I can understand this while trying to compress to a much smaller file size but at half a meg?

Inquiring minds want to know.

Shot with good equipment - A Sony a500 12mp camera with an APS-C sensor.

674k


1.7 meg

NormPR

Can't answer the question, but I have taken some sunrise and sunset pictures that came out like yours on the periphery of every brightness change. I played with them in Elements and finally gave up because they looked fake, (or HDR)...Norm

tainkc Loc: Kansas City

This only happens to me when I go to save them as a Jpeg. The only fix for them when this happens is to save them as a larger file size.

My question is why does this happen sometimes. Normally I can save them at a much smaller file size and not have this happen. Hopefully, you and I can learn something.

NormPR

I'm always up for learning something new, thanks.

Searcher Loc: Kent, England

I have jpgs many years old and several of these exhibit the same symptoms or worse. Some have even shown very visible posterization. Apparently it happens mainly with smooth gradients (such as a blue sky).

According to Wiki, compression algorithms use dithering to prevent this happening but it does not always work.

Although I do not have the knowledge to explain the phenomena properly, I am well aware of when it is likely to happen, so I beware of compressing those images to any great degree.

Searcher Loc: Kent, England

I conducted an experiment using your non-banded picture.

Opened in Photoshop and chose the Posterize command, entered 60 levels of colour and got almost the same result as your banded image.

It almost looks as though compression reduces the number of colours in a gradient - others will want to bite my head off for saying this, but try it first.

johnske Loc: Townsville

I think it may depend on exactly HOW you compress it. I used Irfanview to compress it to 461kb and it showed heavy banding. I then used Microsofts powertoy "Image Resizer" (which I usually use) to compress it to 149kb with no discernable banding. I also used Image resizer to compress it to half that (70kb) and there was likewise no discernable banding

Irfanview - 461kb


Image Resizer - 149kb

RichieC Loc: Adirondacks

I suspect it may be the jpeg which is a form of compression. Though I have not seen it this bad unless your settings are very low.

Note that, as has been exhaustively mentioned before, jpeg is a lossfull compression algorithm. It compresses images by taking similarly colored pixels and making them the same color. This makes the code, which keeps track of every pixel color in all three RGB channels, a lot smaller. As your sky is graduated from bottom to top, it is making each band sample the same color blue (I suspect). In detailed areas, you would not be able to easily pick this effect out- but it is there as well.

You can diminish this effect by choosing a higher "quality" compression level jpeg settings. Or adding pixels as you have done, but each time you open and save a jpeg, it runs the same algorithm and diminishes the image details further... ( This does not happen if you do not save and merely open the image) .

Now a long line of people will chime in and argue that their jpegs look just fine, and this degradation effect may be acceptable to them for their use, but the fact that degradation does occur is not an arguable point- it is a scientific fact. Even at the highest settings, some compression ( in this case concerning Jpeg compression = degraddation) abbsolutely does occur! You are just getting the full effect of this degradation in the sky.

What other formats can you save as?

Tiff is also a compression scheme, but is lossless- it does not average pixel colors.

Raw is also lossless.

If all you have available is jpeg, shooting at higher resolution ( more pixels) by choosing "large" or some pixel dimension "1600 x 1400" or whatever( I pulled that out of my hat) or being able to adjust the compression level of the jpeg by choosing "fine" or "ultrafine" or similar will greatly improve this.

Hope this helps- sucks to loose a good photo because of quality.

bigmac115100 Loc: Florida

I heard from Thomas Hawk and Trey Ratcliff that many sharing sites compress the images as they are posted to the forum which can and does cause banding. Flickr being the exception. They post full res fotos. They do this to save on space as they get millions of fotos posted on any given day.If you don't know these guys, just google them.. Both are very knowledgable

johnske Loc: Townsville

Just had another look at these ... after compression, the image that was compressed in irfanview is exactly the same SIZE as the original - if you're going to compress but retain the same size then something has to give for compression to take place. In this case it's the color gradation information.

On the other hand, the MS powertoy resizes as well as compresses :)

PRETENDER Loc: Micanopy,Florida

Excuse my amateur ignorance but am I correct in assuming this discussion is referencing the sky? maybe it's my old eyes but the top photos look like the sky is in layers?

tainkc Loc: Kansas City

Thanks, Searcher. You shook up my memory banks as soon as you mentioned dithering. I remember now learning all of this about colour and noise reduction algorithms when researching why Nikon seems to have better noise reduction over Sony when using the exact same sensor. Thanks again!

Armadillo Loc: Ventura, CA

Tainkc,

This looks like Compression Banding, and may be controlled in the JPG compression settings. You may, or may not, have sliders to control these artifacts. One of the controls will be the amount of compression, this one created th .jpg artifacts you see when too much compression has been selected. The other adjustments are called Chroma Sub-sampling, and these can cause color banding in areas like blue sky.

Michael G

tainkc Loc: Kansas City

Thank you so much, Richie for your response. I do know all about the different formats and what is lossy and what isn't simply from reading explanations on UHH and also because I was curious as to why there are so many ways to save a photo into a file when a lot of these formats are never used any more.

Fortunately this is easy to spot when I am about to save the file permanently as a jpeg because the banding always shows up when I choose the file size in photoshop. I simply save it as a much larger file as I did with this example. It is always good to know the how & why things occur for it helps in the decision making and if pounded into the head enough times, the problem solving becomes much easier.

tainkc Loc: Kansas City

John, I want to thank you also for your response to my question. It is also nice to know how others deal with this problem. Much appreciated!

Like I told Richie, the one good thing is that although not knowing what causes this, It is easily recognizable when I am about to save it as a jpeg and therefore I just save it as a larger file and the problem goes away. I also remember when I first figure out how to remedy this, I ran experiment after saving a jpeg as a larger file, I opened and changed something and then closed it and re-opened it changed something else several times and I was never able to degrade the jpeg enough to notice that the banding or anything else will appear or re-appear. I figure that I am pretty well safe since once I save a tiff or a RAW file (I shoot in RAW) as a jpeg, I am pretty much done with the photo at that point. If I feel the need to touch it up later in photoshop, it is only for something minor and if there is any degradation, it is not noticeable. This is a fun hobby and one can always learn something new such as I did with you.

Tom