David Lorente
November 14th, 2008, 06:24 AM
I'm currently editing a video with footage coming from a XDCAM EX (clips are in 1080p25), and old Betacam SP tapes shot 10 years ago (that's 576i50, obviously) that I have digitized with a Blackmagic Multibridge in Apple ProRes HQ. The final edit will be converted to DVD to sell to the public, so I decided to make a PAL sequence in FCP. The Beta SP clips are working nicely, but the problems come when we put HD clips in the PAL sequence.
The way FCP handles the conversion to interlaced is HORRENDOUS. I can't understand why they still haven't managed to understand the way these things work (that said, Premiere doesn't work much better, and the same can be said about most NLE's). And it is so simple. In case some smart guy responsible of this is reading the forums, I will explain it, just open your ears:
1- Fields are in fact independent frames. Back in the era of vacuum tubes, when television was invented, engineers saw that resolution could be somewhat improved by using the interlacing trick, but that was just that, a trick that displaced consecutive frames by half a line vertically.
But, when things became digital, instead of conserving the independency between fields, some smart guy thought that two fields could be blended to make a full frame. And that's when the problems started.
Because for almost every operation that involves a displacement of the pixels in one or another way, the interlaced frames must be deinterlaced in two fields, processed, and then reinterlaced again. And in most cases, this is not being done properly.
2- When a progressive image has to be converted to interlaced, you can't just pick the odd lines to make the odd field, and the even lines to make the even field. NO. THAT'S NOT THE WAY VIDEO CAMERAS WORK. For God's shake, just read a good book about video cameras, and you'll learn that, in order to produce a good image, without aliasing, flickering, and all the other weird effects related with interlacing, what video cameras are doing is just BLENDING TWO CONSECUTIVE ROWS OF PIXELS IN THE CCD TO MAKE EACH VIDEO LINE. Rows 1 & 2 form line 0, rows 3 & 4 forms line 2, etc. And then, in the next field, they switch pairs. Rows 2&3 form line 1, rows 4&5 forms line 3... And this applies not only to SD cameras, but also to HD cameras.
So I just wonder WHY AREN'T NLE'S WORKING LIKE THAT. Just give it a try, put an HD clip in a SD sequence, and you'll discover a full bunch of weird effects.
3- Here is the workflow to do a proper progressive HD to interlaced SD conversion:
a- scale down the frame to the SD format of your choice.
b- generate the fields by blending couples of lines, just the way CCD cameras work
And you may be thinking: Does not Compressor convert one scanning method into another? And the answer is: NO. It just performs a resizing, but there is not any kind of processing, even forcing the settings in the "Frame controls" tab.
I think we, as users, tired of obtaining dissapointing results not by our fault, or by a bad quality footage, but by bad implementation of image processing in the NLE's, we should made pressure to software developers to solve these problems. Because I don't need more absurd special FX and transitions, or the capability to handle a hundred video tracks, or other useless things, but I ABSOLUTELY NEED TO KEEP A GOOD QUALITY IN THE IMAGE.
The way FCP handles the conversion to interlaced is HORRENDOUS. I can't understand why they still haven't managed to understand the way these things work (that said, Premiere doesn't work much better, and the same can be said about most NLE's). And it is so simple. In case some smart guy responsible of this is reading the forums, I will explain it, just open your ears:
1- Fields are in fact independent frames. Back in the era of vacuum tubes, when television was invented, engineers saw that resolution could be somewhat improved by using the interlacing trick, but that was just that, a trick that displaced consecutive frames by half a line vertically.
But, when things became digital, instead of conserving the independency between fields, some smart guy thought that two fields could be blended to make a full frame. And that's when the problems started.
Because for almost every operation that involves a displacement of the pixels in one or another way, the interlaced frames must be deinterlaced in two fields, processed, and then reinterlaced again. And in most cases, this is not being done properly.
2- When a progressive image has to be converted to interlaced, you can't just pick the odd lines to make the odd field, and the even lines to make the even field. NO. THAT'S NOT THE WAY VIDEO CAMERAS WORK. For God's shake, just read a good book about video cameras, and you'll learn that, in order to produce a good image, without aliasing, flickering, and all the other weird effects related with interlacing, what video cameras are doing is just BLENDING TWO CONSECUTIVE ROWS OF PIXELS IN THE CCD TO MAKE EACH VIDEO LINE. Rows 1 & 2 form line 0, rows 3 & 4 forms line 2, etc. And then, in the next field, they switch pairs. Rows 2&3 form line 1, rows 4&5 forms line 3... And this applies not only to SD cameras, but also to HD cameras.
So I just wonder WHY AREN'T NLE'S WORKING LIKE THAT. Just give it a try, put an HD clip in a SD sequence, and you'll discover a full bunch of weird effects.
3- Here is the workflow to do a proper progressive HD to interlaced SD conversion:
a- scale down the frame to the SD format of your choice.
b- generate the fields by blending couples of lines, just the way CCD cameras work
And you may be thinking: Does not Compressor convert one scanning method into another? And the answer is: NO. It just performs a resizing, but there is not any kind of processing, even forcing the settings in the "Frame controls" tab.
I think we, as users, tired of obtaining dissapointing results not by our fault, or by a bad quality footage, but by bad implementation of image processing in the NLE's, we should made pressure to software developers to solve these problems. Because I don't need more absurd special FX and transitions, or the capability to handle a hundred video tracks, or other useless things, but I ABSOLUTELY NEED TO KEEP A GOOD QUALITY IN THE IMAGE.