9 Replies Latest reply on Jan 11, 2010 7:41 AM by lmaclanphere

    masking and file size

    lmaclanphere Level 1

      hi all

      first post here, and very basic question:

      does masking a part or parts of a video sequence reduce the final file size compared to an unmasked version of the same project?

      thanks!

      LML

        • 1. Re: masking and file size
          bogiesan-gyyClL Level 3

          No.

           

          bogiesan

          • 2. Re: masking and file size
            lmaclanphere Level 1

            thanks man

            so, would it be smart to crop video before importing if I'm only going to

            use a portion of it?

            LML

            • 3. Re: masking and file size
              Andrew Yoole MVP & Adobe Community Professional

              It's a little unclear what your goal is.  What do you actually want to achieve by masking or cropping your footage?  What format is your source footage?  What do you want to finish up with?

              • 4. Re: masking and file size
                lmaclanphere Level 1

                let's say I have video, any format, of a person's face.  All I want to use

                from that video in my AE comp is video of a single eye.  I can mask that

                really easy, but as I understand, all that masked video of the rest of the

                face is still going to count toward the final file size--say in a .mov that

                I want to email, or publish on the web.  If I could easily crop out a bunch

                of the face, rather than mask, wouldn't that give me smaller files?

                thanks again

                LML

                • 5. Re: masking and file size
                  Todd_Kopriva Level 8

                  If you start with, say, a 1920x1080pixel image of a face and then "crop" the image so that you're only exporting a 100x100pixel image of an eye then, yes, you will have a smaller file. If, however, you export a 1920x1080pixel image of an eye with a whole lot of surrounding black, then you won't have a much smaller file---unless you are using a compression scheme that takes advantage of how easy it is to encode large amounts of solid color.

                   

                  So, the answer is "kinda".

                   

                  To answer the question that you seem to have come to after your original question: Yes, if you're only going to use the eye, then it will be useful to have a movie that contains nothing but the eye.

                  • 6. Re: masking and file size
                    lmaclanphere Level 1

                    I think I'm getting it:

                    if I were to render/save using a jpg compression then, the black/masked

                    version would be smaller than the same project without the mask.  But

                    probably not as small as if I had simply cropped the original video to the

                    size that I needed in the first place?

                    sorry for dragging this out....

                    LML

                    • 7. Re: masking and file size
                      Mylenium Most Valuable Participant

                      if I were to render/save using a jpg compression then, the black/masked

                      version would be smaller than the same project without the mask.

                       

                      Not necessarily. The JPEG algorithm (or any MPEG for that matter) is based on subdividing images in uniform blocks and then deciding how to compress data within these blocks. That in essence means for each block still a lot of data is generated, telling where this block is located, what colors it contains etc.. True, the "empty" areas would compress a bit better than your fine details, but you have no choice of compressing those areas more agressively than the desired content. The file size therefore is almost linear to the compression quality you choose - good quality = larger file, bad quality = smaller file. What you would want instead is RLE/ LZW compression that basically works by detecting identical data and encoding it only once. So instead of writing e.g.

                       

                      (black,0,1),(black,0,2)....(black,0,1920)

                       

                      it would simply write

                       

                      (black,0,0-1920)

                       

                      for the same row of black pixels. The more identical data, the greater the savings, regardless of actual resolution. Of course it's a bit more complicated in reality, but you get the idea. Formats supporting LZW/ RLE like compression are for instance SGI, TGA,TIFF, BMP, OpenEXR, PNG and ultimately of course also GIF. Just try it and you will see.

                       

                      Mylenium

                       

                      Message was edited by: Mylenium, damn typos again

                      • 8. Re: masking and file size
                        bogiesan-gyyClL Level 3

                        > first post here, and very basic question:

                        does masking a part or parts of a video sequence reduce the final file size compared to an unmasked version of the same project?
                        thanks man

                        so, would it be smart to crop video before importing if I'm only going to

                        use a portion of it?

                         

                        As you've seen, the answer is mostly "no" with a bit of "not really" offset with a little "and it depends."

                        Being new to After Effects is not a sin, we were all new to this at one time or another and, man, After Effects is supremely complex. But your original post exhibits a fundamental misunderstanding of so many basic things. I shall offer a bit of advice: One does not ever consider file size when working in After Effects. AE is a content creation utility. Your file sizes are determined by your output mechanism and compression application.

                         

                        bogiesan

                        • 9. Re: masking and file size
                          lmaclanphere Level 1

                          cheers

                          thanks everyone for the info (and patience)

                          LML