Photoshop: Gradient pink - red

[Madeliefste Oh]

I came across something I have never seen before. I want to use a highlight on a teapot. The base color of the teapot is pink red. In Photoshop the gradient is smooth, however when I upload to SL there appears a darker spot between the highlight and the base color. And is seems it has to do with the color red, because when I use for example a blue base color for the teapot, the problem does not appear.

 

Any one who knows what is happening here? And even more how it can be cured?

[Chosen Few]

My guess is the banding is an artifact of JPEG2000 compression. 

If you take a look at the individual color channels in the image you posted, you can see the blue channel is the culprit.  For whatever reason, that channel did not compress very well.

Open up your info panel, and in each channel move the mouse over the gradient in both sections of the image, and take a look at how the color values change.  In the Photoshop part, you'll see that in all three channels, the values change smoothly, in one-stop increments, as you slowly move the mouse from the base color area, inward toward the specular highlight (and of course it jumps up abruptly when you actually hit the highlight).  In the SL version, however, it's a different story.  The red and green channels behave similarly, although a bit less smoothly, which is to be expected after compression.  The blue channel is out of whack.  The values rise up and down, as you cross each band. 

The area you described as "dark" has less blue in it than the base color has.  The reds and greens are actually brighter in that area than in the base color, just as they should be.  The lack of blue, though, is enough to cause a drop in the combined brightness of the three channels.

One thing you may find interesting is that the very same bands exist in the blue channel, in the Photoshop image, too.  Their values are arranged in the right order, though, keeping the gradient effect behaving as expected.  Each concentric ring increases in color value, as you approach the middle.  When the compression algorithm was a applied, it must have recalculated each color separately, and the way the math happened to work out, some of the blue bands got decreased instead of increased.

 

Unfortunately, there's not a lot you can do about it, since SL's JPEG2000 compression settings are not under our control as users.  I would suggest experimenting with different color schemes.  When you find colors that make the problem apparent, avoid those colors.   I doubt there's anything else you can do.

[Chosen Few]

One more thing I forgot to mention in my last post:

If you're saving your images as JPEG, that can be a major contributor to problems like this.  So, if you've been using JPEG, stop. 

JPEG is lossy, and so is SL's implementation of JPEG2000*. So, when you start with a JPEG, and then SL converts it to JPEG2000 for upload, you end up with the 'copy of a copy' effect, and the results are sometimes pretty ugly.

For best results, ALWAYS save your images in a lossless format.  TGA is the industry standard, but BMP and PNG will also do the job. 

Don't worry about the file size for the locally saved image, by the way.  When you upload an image to SL, the viewer software makes a copy, and converts it to JPEG2000.  It is that copy that gets uploaded.  The source file never leaves your own hard drive.  The JPEG2000 file that does get uploaded will be the same size, no matter what the source format.

 

*Note: SL's lossless upload feature only works on very small images, like sculpt maps.  For medium and large sized images, it's always lossy, even if lossless upload is enabled.

[Madeliefste Oh]

Thanks for the insight, Chosen.

Before I posted here I tried all kind of things, included uploading in different formats. The picture shown is the result of uploading a png 24 bits. I also tried tga en jpg. I never use jpg as upload format, but in this case it actually gave the best results. Still not good enough, and only slightly different, but still I was surprised.

Might have to do with that the jpg contains less color info already, so the JPG2000 transfer gets less mixed up in this color range that seems hard to handle for JPG2000.

[Chosen Few]

Interesting.  Yeah, I'd have to agree that perhaps the JPEG save had already filtered out some of the colors that the JPEG2000 utility does not handle well.

[Tenly]

I have this same problem of banding even when the blend is of the same color..gradient from 100% to 10% for example. I use Fireworks and save out PNG at 32 bits transparent @ 1024x1024. Im stumped and seems like no one has an answer other than SL is likely re-compressing the image into losing information even when its a PNG or a TGA.

[Madeliefste Oh]

In my case it turned out to be a problem of communication between SL and my graphic card. I just had installed a new graphic card, and something in my settings (I don't remember what exactly, it's some time ago) was not finetuned yet for the use in SL.

Since I did adjust the settings for better 3D performance, the problem never occured again