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View Full Version : Difference between PNG24 & PNG32??



virtualcomposer
10-31-2008, 03:57 PM
I'm going to be rendering a project out soon and know it's best to render them, if you want high quality, in PNG formate since you don't lose the alphas & RGBs. What is the difference between PNG24 & PNG32? I want the highest quality possible. I used to render output with QT but fustrated if the power popped out or tried to composite it into something else, it wouldn't look right. I was also wondering, when I rendered out with QT, only the objects would be visible when compositing and any blank space that was left was invisible. Kind of a nice feature. Is PNG like that or will I have to chroma key it out?

Dexter2999
10-31-2008, 04:16 PM
I think the difference is that the 32 preserves Alpha in that last 8 bits. The 24 doesn't. At least that is the way the Targa works.

virtualcomposer
10-31-2008, 04:17 PM
So it's better to save in the PNG32 then if at all possible?

Hopper
10-31-2008, 05:35 PM
Didn't we have this discussion before? The way 32bit isn't actually 32bit, it's 24 with additional Alpha, etc... I could have sworn...

JeffrySG
10-31-2008, 09:07 PM
Yeah, 32bit PNG is a 24bit with an 8bit alpha. Test a few frames and see what format will work the best for you. I don't like the 32bit PNG files as when you open them in Photoshop there is no extra alpha channel but the objects are on a transparent background. I'd rather have an alpha channel and decide for myself if I want to remove the background. Like on a 32bit TGA.

Or you can save off a 24bit file - any format - and also save off a 8bit mask file...

virtualcomposer
10-31-2008, 11:30 PM
So what would be better then? TGA or PNG? I'm so used to rendering out in QT that I'm oblivious to these two formats. I want highest detail and clear background and rare do I mess with alphas.

Dexter2999
10-31-2008, 11:38 PM
I use TGA32 as a general rule. I almost exclusively do spinny logos. I preserve the Alpha then comp the logos over Motion Backs or or graphics elements.

I also never render to Quicktime. I strongly recommend getting used to rendering in Image sequences. This way should your computer crash for any reason, you can find the last frame rendered and pick up from there. With any sort of AVI, WMV, or Quicktime if your computer dumps in the middle almost guaranteed that you have lost that work and have to start from scratch.

I think just about every editing package will import the image sequence as a clip. Even if your editor won't, you can assemble the sequence as a clip inside LW. You open a new scene and import the image sequence and map it to the background. Then you render an empty scene with the sequence now being recorded to a movie file.

Hope this helps.

virtualcomposer
10-31-2008, 11:43 PM
Yes, it helps a lot. Thanks for all the great info. So many things to learn! That's why I love this field. It never gets to the point we know it all. I think I've mastered about 1% of animation. The rest will probrably take me another 20 years. LOL

dwburman
11-01-2008, 12:20 AM
I render both PNG32 and TGA32 depending on how I feel at the time.

You shouldn't see a quality difference between the two. PNG uses a lossless compression scheme (the picture isn't degraded to save disk space) and usually TGA is uncompressed.

IF you save your file with an alpha channel (tga32 or png32 both do) and the software you're using those files in supports the alpha channel, you should be good to go.

Incidentally PNG and TGA are called 8-bit color depth file formats. Each color channel is 8 bits (256 levels of gray) so RGB=8+8+8=24 & RGBA=8+8+8+8=32. The 24 and 32 are the total of all the color and transparency channels.

These days you can use file formats that give you more color information than PNG and TGA. They won't give you more pixel resolution but will let you adjust the exposure and colors much more before the picture degrades. You may want to look into the Open EXR format or any of Lightwave's filesavers with FP (FP=Floating Point) in their name as well as .hdr and .cin and a few others.

Of course, more color information often equals larger files so you need to take that into consideration as well.

sfjedi
03-27-2009, 07:05 PM
With any sort of AVI, WMV, or Quicktime if your computer dumps in the middle almost guaranteed that you have lost that work and have to start from scratch.

This is not true with WMV single pass encoding. WMVs are also great for stitching pieces together w/o the need to reencode (assuming both WMVs you're stitching have the same compression settings). One trick I like to do is to actually copy the WMV file to the same directory while it's actively encoding so I can play the copied file and preview its quality and progress. Then you just delete the copied file and wait for the encode to finish.

Oh, and stitching WMVs together is free. Just download Windows Media Encoder 9 series and tell it to encode both files together. If they are of the same compression settings it will skip the encoding process altogether and output your new file in seconds!

I've never been able to recover an AVI successfully, so I'm to presume they would be corrupt if interrupted for any reason.

I haven't played with Quicktime format, so I can't say definitively about that, but I wouldn't be surprised if it had the same problem as AVI.

Greenlaw
03-28-2009, 01:07 AM
I'm going to be rendering a project out soon and know it's best to render them, if you want high quality, in PNG formate since you don't lose the alphas & RGBs. What is the difference between PNG24 & PNG32? I want the highest quality possible. I used to render output with QT but fustrated if the power popped out or tried to composite it into something else, it wouldn't look right. I was also wondering, when I rendered out with QT, only the objects would be visible when compositing and any blank space that was left was invisible. Kind of a nice feature. Is PNG like that or will I have to chroma key it out?

Hi,

This is all pretty basic info, but maybe new users will find it helpful:

There is no difference between 24- and 32-bit other than an alpha channel which makes up the extra 8-bits. The quality of the color channels is identical in both of these formats. This is true for TGA or PNG. The advantage with PNG over TGA is that it's more compact, but like TGA it's a lossless format. (As opposed to JPEG, which is a lossy format and does not allow alpha channels.)

You only need the alpha channel if you want to composite the image over a background or for combining it with other cg elements, or if you want manipulate the image in a particular way using a post-processing effect. It sounds like you do.

Now, if you're really interested in the highest quality, use EXR This format can not only have a significantly broader range of color, but it also can contain many auxiliary channels like depth, motion vectors, normals, and shading properties, just to name a few possibilities. Because of the higher range of colors, this format can prevent banding that often occurs with 24/32-bit formats, and all those extra channels help you manipulate your rendering in all kinds of crazy ways with the highest precision. This is assuming you actually want to composite or alter your renderings in a program like After Effects or Fusion. Bear in mind that if you enable all the bells and whistles available with EXR, the files can be huge. Most of the time, you will only need a few auxilliary channels, so use your judgement.

FYI, we generally use PNG for textures (index color for most textures, and higher bit depths for textures with subtle grads like sky maps,) EXR for CG renders and sub-comps. If the final output of a job is for video, we usually give the client TGA files, sometimes with a sensible alpha channel if the client hopes to manipulate the image further elsewhere. Clients for video productions (like TV shows and commercials) generally prefer TGA because it's a fairly universal format that almost anything can read. For film productions, clients will usually want something better, like Cineon or maybe even EXR.

(I think there is a thread where we went into more detail about how and when we use the PNG format; it was quite a while back but should turn up in a search.)

The are many good reasons why you should not render CG directly to a movie format like QuickTime or AVI. One is the potential corruption problem you mentioned, which can waste a lot of time. Rendering can be more stable when rendering frames because your computer only needs to keep one image in memory at a time, save it, and then move on to the next one. With a movie format, rendering a long sequence can get a lot more complicated because LightWave has to keep a single file open throughout the entire rendering process.

Another good reason is that you can't network render to a movie format from LightWave, which is a waste of resources if you have extra CPUs available.

When you render single frames, it can potentially save you from re-rendering full sequences. For example, if you made a mistake or get some bad frames, and the error only appears in a few frames, you can correct and re-render just those few frames.

The point is, when you render to frames, you can work more efficiently and you have more options available to you, and when you're happy with your sequence you can easily load those frames into almost any video editor, compositing program, or even LightWave (as a backdrop), and render out your Quicktime or AVI movie as a final step.

Greenlaw