Texture Test, Take a Look!


(ndnchief) #1

Here is a test I did, mind you, non-scientific… file size is about 450 Kb. Sorry about the size for all you 56K’ers, But I needed descent quality so the difference in the results could be seen.

NDNChief

blender.homestead.com/textest.html


(jrt) #2

The .png certainly stands out against the .jpg. Didn’t I read somewhere that the .png format was introduced to get better images on the Internet? I never understood why it wasn’t more widely used. How does Blender cope with them?

jrt.


(OTO) #3

Hello ndnchief,
your intentions are good but you miss some points, i guess, i’m far from
an expert on image file formats.

You can’t save PSD or TGA in JPG format cause, in my opinion, they
have layers, or an alpha chanel not suported by JPG.

And above all, the file size( not the quality) of PNG images is bigger (in most
cases) than the JPG.
Your exemple it’s not a good one!! Phew colours :slight_smile:
And maybe it’s an indexed palette image.

Take a 24 bit coloured photo image and then save in PGN and Jpeg
and you’ll see!!??

And some more little details
Bye
António


(z3r0 d) #4

… ok, Do I have to explain jpeg, png and targa-s to you guys?

They all can* have alpha channels. And they can all be compressed.

The comparison sort of ends there.

Png-s alpha channels are not very well supported (in web browsers at least), and png-s make a good replacement for Gif images. Unlike Gif images png-s do not have to be limited to 256 colors, and can have different levels of opacity in their indices (if indexed). They are not lossy (unless you make them indexed), so they retain their quality, but seem to end up being very large. Pngs are best for images with fewer colors in large shapes (if you want a small file size). A png of, for example, this forum would be compressed much better than a photo of, say, a field of corn. PNGs can be of nearly any color depth I can think of (though support is not guarnteed)

Jpeg-s are compressed in a lossy format. They loose the accuracy of the image by considering that defects that are small enough will not be noticeable. If a jpeg were zoomed in it would appear that the defects come on the edges of 8 pixel squares (which may be true). It also, at that level seems to have some oddly colored pixels as if it were dithered (which they are not). They are better suited for photos, especially online, where loosing quality is not much of an issue. They have trouble with vector-graphics style work (where png would be better) in lower compression levels (as evident by the link on the thread-starting-post). The best file size usually at about 75% quality. I believe the colordepths that are supported are 24bit (true color), and I know grayscale.

Targa images seem to be the bitmap of the bunch. I believe they are stored mostly uncompressed. I think the lzw (??) compression is a very simple compression to help shrink files that have large patches of the same color. (I honestly don’t know, I know about png, and jpeg for web work). They seem to be 24 bit, or 24 bit with alpha channel.

  • blender will render to a 4 channel jpeg (with the lowest compresion), and work with it approaitely, but most programs I have seen will believe it is corrupt.

Terms which you may want to know
indexing - having the colors in an image refer to an index in a list of colors
dithering - approximating higer color depths by having adjacent pixels have different colors, that when blended together by the viewer (you, or I), appears to be more colors.

I need to get to class.


(OTO) #5

Hi z3r0 d

Sure you can explain, please, but be precise, especially when you use
such a “heroic” style!!

JPEG format don’t suport alpha chane (just try to save
a image with trasparency in it in a JPG format??)
Tga images with alpha chanel are a 32 bit images
PNG have a 48 bit deep capacity

Bye
António


(ndnchief) #6

It seems that while there is debate on this issue, most everyone really is saying the same thing.

  1. That Jpeg does compress images to a smaller file size than PNG.
  2. That Jpeg is lossy while Png is not, so Png keeps the integrity of the original image better.
  3. Though Jpeg is a lossy, and (supposedly) the loss is not discernable to the human EYE, I usually can notice when image is placed side by side, but would not really matter if the original is never seen.
  4. That when you have an image of say 2 or 3 colors, Png can save that image in a very small file size, which may actually be smaller than JPEG can save at.
  5. For images of multiple colors JPEG would most likely be a good choice, where as PNG does not handle filesize well with images of multiple colors.
  6. I have only used PNG on those textures Posted in this string, only two colors. I will try it with a true photo image as OTO suggested and tell you all my results, Im sure OTO is correct.
  7. I thought that z3r0 d post was pretty informative, as all of them were, I didn’t think he was pushy in his response. Though I must say, I have never known of any JPEG format to support ALPHA Channels. Mabey that was a typo.
  8. Mabey PNG format does handle images with only 1 to 2 colors, smaller file size and better quality image, than JPEG format. But on a whole JPEG format compresses much better than PNG on images of multiple colors.

Just my thoughts… Thanks all for being so responsive, makes the learning curve much easier. Oh, and I did say that I had very few controls in place when doing this small test, and I certainly am no expert, So results may Vary, LOL…

NDNChief…


(OTO) #7

ndnchief you’re a wise man!!! :slight_smile:

(just a fast sugestion, not verified. If you have few colours
and no gradients in your image, make it an Indexed one, with
a 256 pallete, and save as PNG maybe the size decreases a bit??)

Bye
António


(z3r0 d) #8

Maybe I was … um prickly.

Uhh, no jpeg usually does not do alpha channels, but I believe blender will render, and save one. And it will read it correctly.

I have not seen another program that could work with that file. if I were allowed to here (or had blender on a disk), I would upload one…\

I put (what I think is one) at http://mywebpage.netscape.com/YinYangEvilSane/alphaContained.jpeg

I have never tried a 32 bit jpeg (one with an alpha) in the renderd version, but they work in real-time mode.


(OTO) #9

No problem!!
All the people have some …obssesions :slight_smile:

When i’ve clicked in your link, my browser “said”

/alphaContained.jpeg” cannot be displayed, because it contains errors.

Is this enough??
Bye
António


(z3r0 d) #10

That image hasn’t worked for me in web browsers.

That was my point.
Try it in blender. Maybe uvmap it to an alpha face.

It should work fine there.