Why PNGs?

What is the advantage to rendering .pngs? Some people post with them and they take a crapload of time for me to load. Why not use .jpg’s?

The .png format is lossles - no compression and supports alpha-chanel. Why people use it on internet? Well, it could be that they are too lazy to save it like .jpg

PNGs have a better compression than GIFs. If people are posting really big ones they’re probably not compressing them as highly as they can (a lot of software defaults to a medium compression, even though PNG is lossless no matter what level of compression is applied).

For posting, a JPEG is usually sufficient. However, sometimes a PNG is more desireable since you don’t loose any color information.

If you’re making an animation, you should render to PNGs. Only apply compression to the final AVI (or MOV, etc).

The .png format is lossles - no compression and supports alpha-chanel

  • Png does compress, lossles means that from the point you first compress you can save over and over again whitout any more loss, png also stores an alpha chanel.

  • Gif works with an indexed palett so when you first create your optimal palett you loss a lot of colors (only 255 remain) but from now on a gif file is lossles because it keeps the link to the palett color to each pixel (pixel 20 = color 232 [color 232 = R 214, G 56, B 173])

Gif can also handle animations, you create them with multiple layers and a name convention were you specify the duration of each frame etc.

  • TGA & BMP files are true uncompressed AND lossles formats becouse they store RGB values for every independent pixel. TGA can also handle an alpha chanel and can have a lossles comprecion if you whant to.

  • Jpg compresses every time you save it, so It keeps loosing colors. It works detecting similar pixels and make them link to a same RGB stored value.

  • Png does compress, lossles means that from the point you first compress you can save over and over again whitout any more loss, png also stores an alpha chanel.

This not quite right. First of all “resaving” a jpg will genrally not make it worse, because it lossy, it dumps information that is more or less not noticeable. If the source image is a jpg, the the information that it dumps it just not there. So resaving a jpg multiple times will not make it worse.

PNG’s on the otherhand dump no information. It uses filters and compression and the result is exatly the image data you started with. Even if most of the “information” it not “visable”

So PNG’s are good to reduce “noise” artifacts that can creap into lossy formats. But for a photgraphic type image, its less that ideal. A jpg will be a lot smaller.

Jpg compresses every time you save it, so It keeps loosing colors. It works detecting similar pixels and make them link to a same RGB stored value.

again not quite right. It redusces the resulotion of the colour info and keeps the lummance info the same (saves about 50% ) . The rest of the compresion is based on the discreate cosine transform on 8x8 blocks. this is why you get that blocky effect when the compresion is too high.

delt0r

JPG DOES lose info over multiple saves and i can PROVE it… i do a render and save as jpg - 100%… and it seems to save fine…
i go into photoshop… add my copyright… possible title… or others image enhancements… and save again as a jpg - 100%… and thre sill be NOTICABLE differences between teh two images… mainly the degredation of antialiasing of sharp edges making them much blockier… if you further wish to argue this… i will post comparison images.

I never save JPEG from Photoshop. I have resaved jpeg from gimp (and other programs also using libjpeg) without any noticeable degradation. In gimp you can preview on an enlarged image. Using the same compression used in Blender seems to work very well.

Also, JPEG images saved from Photoshop carry about 4 Kb of garbage, at least that is what jpegtran removes.

Photoshop also adds waternarks…What info is embedded in the watermark is anyones guess.

Likewise i use gimp… Resave many many times… No problem.

But you said that you add things… If you change the image… Well then you change the image. Its not going to be the same, then is it. But visable quality should not drop. It doen’t for me.

JPG is lossy. IF your still doing post production, you should use PNG or tga. Even digital movies use a lossless storage for much of the postproduction process.

I have writen jpg decoders. I know how jpg works…

I sujest using a product that can handle jpg’s better. Case in point Photoshop has a history of being a little quriky with some image formats.

Delt0r

Lossless, open source, 32-bit alpha.

Need I say more?

I prefer jpgs though for internet use. Smaller (I pity 56k users, I was one once…26.4kbps), people can’t “steal” it if it’s got nasty ugly artifacts etc.

I don’t like viewing PNG images on the internet. To me it says that the person posting it doesn’t care that anyone copies it, or it means they are too lazy to make it into a JPG. Sometimes I am on 56k, when I am not at home.

I post copies of my original work as JPGs on the interent. If I want the image to look good, then I adjust the JPEG compression ratio to almost none.

For editing, I have used full blown bitmaps (BMP) in general, except when I need to use an alpha channel, then I use PNG.

Lazy? It takes more work to get it to a PNG, because everything defaults to JPEG. But I really don’t like the compression on JPEG, because it distorts it. I’d much rather have PNG with nice, clear graphics, even if it is a bit larger in file size.

hmm

Lazy? It takes more work to get it to a PNG

not if you save it as PNG directly from blender. It does even make a alpha channel for you if you want.

jpg is best for internet, PNG is best when you work with your image. Thats my opinion.

What I mean is that Blender defaults to JPG too. You have to go and change it in the settings. Trivial, yes, but still technically more work than JPEG. :stuck_out_tongue:

I like using PNGs on the internet because it supports FULL transparency with FULL colors, unlike GIFs. Please note that the transparency only shows up in non-Internet Exploder browsers, as Microsoft was too dumb to put in full PNG support into IE ¬_¬ Yay Firefox and PNGs!

Now for very large images I’ll use JPEGs with a very high quality settings, but for most anything else I use PNGs.

I find generaly that PNG has a poor conpression rate.
So if I don’t find it important to preserve the exact image I rather use gif for solid color image compression and jpg for photo image compression.
But only for images that I post on the internet.

I never compress any images that I save and/or print, it’s just not worth the harddisk save compared to the time I lose on compressing and de-compressing. RLE Targa is just fine: fast little compression, 8/ 16/ 24 & 32 bit support and everybody and everything can read .tga

PNG compression is better than GIF’s. Unless the program you are using has a poor PNG implemetation. Almost all perfonace “gains” for GIF is due to the fact that it can have only 256 colours. But PNG can have many more. convert the image to 256 colours and then save as a PNG (use gimp) and you will find its smaller.

What happened to the whole Licenceing of GIF, cus someone patened it? Is that still going on?

delt0r

Unisys was the patent holder. Their patent has expired here in the USA, but may still hold sway elsewhere. In any case, it is perfectly legal to use GIFs, e.g. on a web page. It is illegal to sell, give away, whatever, software that either encodes or decodes LZW GIFs without paying a hefty royalty to Unisys where their patent is still in effect.

PNG has several compression schemes. Depending on your image, one might work better than another. The only way to guarantee the smallest filesize is by applying each one and choosing the smallest output.

Another thing is that GIFs store image data as an eight-bit (maximum) index into a color palette. No matter how you compress it, a TrueColor image is going to compare poorly with a GIF of the same image, simply because the GIF throws away color information. You might be able to get around this by a clever combination of Local Color Table, Graphic Control Extension, and Image Descriptor Blocks, but I don’t think anyone has ever cared to bother.

To get comparable results, using your favorite image editor, convert your image to indexed or colormapped mode, with a maximum of 256 colors, then save as PNG. The PNG will be significantly smaller than a GIF 90% of the time. And definitely dial-up friendly.

MNG is the animation-friendly version of PNG. So GIF-animations can be converted, almost directly, into MNGs. All you need is a browser capable of properly displaying one…

I hadn’t considered that my 24-bit PNGs were so large. I’ll have to go back and convert them to JPEG for you all.

when it comes to photography jpeg is the worest format you can use next to gif, which some people use.

png not only has nearly no compression artifacts but also delivers unchanged colors which gif does as anybody should know (265 colors) and jpeg does change the colors as well.

sure the images are smaller with jpeg but color wise not as good as the png version. if you are serious about delivering good images / photos use png.

56k modems arent the standart anymore :wink:

Maybe not in the USA and the richer parts of Europe, but a lot of people around the world are still using dial-up.

JPEG was designed specifically for photographic image compression. If carfefully used, it can produce near-photographic quality. If you have a business processing photos or other high-quality color images, then you’re right. Use something lossless instead. Otherwise JPEG works just fine.

For tiny images, using JPEG over PNG or GIF is almost pointless.

And what about PNG over other formats as TIFF for large images?

I have been using PNG also for my very large images. I used to use tiff and long before that IFF ILBM. Everytime I install Linux or upgrade the Gimp I have to recompile libtiff with the lwz compression patch because otherwise I get a message saying “LZW compression no longer supported due to Unisys patent enforcement” when I attempt to save. I don’t think it applies to my country, but that makes me feel like a criminal, so I switched to PNG. PNG also usually compresses better than LZW.

Some of us also have slow broadband internet… :stuck_out_tongue:

About the watermarks in jpeg files from Photoshop, I always had a feeling I had to stay away from it…