Some updates - for the few still interested in this project...
Black crushing & white clipping (supposed) problems
I thought I captured the laserdiscs with wrong settings (default)... so I took one of the laserdisc I captured before, and did some tests. For example, I took the scene right after the opening crawl: I let the laserdisc player play that scene over and over, and with the Virtualdub histogram in capture mode I discovered that the image histogram (luma values) are inside the left and right borders, except when there are explosions, with flashes the image with totally white screen - only in that case, the right border (white luma) stay a bit out of border; I don't think this is a problem, so I decided to not recapture the laserdiscs again, as the default settings are 99% accurate.
But I realized that my captures' luma range is 0-255, and not 16-235 as I thought before... it's true that the "extend luma white point" and "extend luma black point" in Virtualdub capture mode make the image "tv compliant" - infact, when flagged, the image range is "compressed" and forced to stay in the 16-235 luma range, but the exceeding black and white parts are clipped... so, if I use Avisynth to convert my capture from full range 0-255 to tv range 16-235 will be the same, if not better - and if I will decide to release a full range version, I will just not do the conversion! Obviously this fact applies also to my OUT captures... hope this fact will help someone else!
Color correction
At the beginning, I was sure that all the movie had wrong colors, so I was testing the same color correction settings with different scenes, and in some it was perfect, in others so-so, and in others completely wrong... so I realized that only some scenes are affected by the pinkish tint, and many are good "as is"...
To test my assumption, I ran the whole movie through an avisynth script: on the left, the unprocessed movie, on the right, the movie with autowhite corretion; the second part of the movie is almost all color correct, as both images are quite the same. Of course, the initial scenes inside the Tantive corridors and in Mos Eisley were afflicted by the pinkish tones.
But not all the scenes with wrong colors were corrected in the right manner by autowhite (obviously, as it is a "stupid" filter, as written also in the avisynth wiki)... for example, in the desert scenes, sometimes the sand were yellow - instead of pink, so it was right, but sometimes it was grey!!! If the autogain is applied, many times things get better, but the contrast fluctuated a lot, and in few cases there are on overly exagerated grain in the whole picture.
It's safe to say that autogain CAN'T be used for color correction, but autowhite can, in limited cases - at least, this is what I have discovered during my tests. But, HOW can I use autowhite, where it make its work good for a part of a scene, and bad for another? Must I use it for the whole movie, check where the job is wrong, and change the wrong scenes with my own color correction?
At the end, the usual little 25-watt light bulb appeared over my head... what if I use a median of three color version of the same image? the first will be the unprocessed, the second will be the autowhite corrected, and the third the manual corrected... if the first and second would be (quite) the same, the manual correction will be discarded, if the autowhite is overly exagerated or plain wrong, the result will not contain that...
Well, I did some tests along the whole movie, using four quadrants (unprocessed, autowhite, manual correction, median) and I exclaimed: "in media(n) stat virtus!" (virtue stands in the middle)... it corrected all the autowhite problems.
I'm also thinking about getting an hardware color corrector (I'm after a cheap Sony XV-C900, PAL) and use it instead of avisynth... it will color correct real time, with its two joysticks for black and white adjust... what do you all think?
Last thing: as my captures are YUY2, I used ColorYUV (and ColorYUV2) avisynth filter for color correction, to avoid any conversion to RGB and back... but at the beginning, I applied the color correction to YV12 video! And discovered that, despite the fact that the filter works with YV12 too, the results sometimes are completely wrong! So, the lesson learned is: color correct YUY2 video with ColorYUV BEFORE converting the video to YV12! (^^!)
Comb filter and rainbowing
On my OUT project, I used the same capture chain used here: Pioneer CLD-D925 laserdisc player, S-Video out to the capture card, with Philips SAA-713x chipset. I chose to use S-Video instead of composite, because, after all the tests I've done, it seems that the result is slightly better; also if the capture card comb filter for PAL signals should be 4-line, Vs CLD-D925's 3-line, the composite output is just a recombination of the S-Video signal, so I think it's wiser to use the player S-Video directly.
But I tested also other laserdisc players and units - CLD-600 and LD-V4300D, both directly, via composite to capture card, and through DVD recorders - Pioneer DVR-320S and Panasonic DMR-HS15 - used as external comb filter.
It's difficult to get information about the comb filter type present on these DVD recorders; I found that the DVR-320S has a 3D comb filter, but unfortunately it works only with NTSC... with PAL, it *could* be a 5-line type, that *should* be better than capture card's one... about the DMR-HS15, many praise its TBC, but it's not needed when capturing laserdisc, as any laserdisc player has one built-in...
By the way, I remeber that when I tested those players through the DVR-320S, using Video Essentials' Snell & Wilcox zone plate, its comb filter was really good - as a good 3D comb filter it's better than 4 or 5 line one. But using the DVR-320S with PAL signal didn't improve the quality... at least, my own eyes didn't see any difference between its comb filter and the capture card's... if only I could have a PAL test card on laserdisc to test it... OR... if I take a PAL test card, 720x576, and let a computer play it through its composite output, then capture its composite output with my capture card composite in, and also with the DVR-320S and DMR-HS15, then I could clearly see which has the best comb filter, right?
Other reasons I avoided using a DVD recorder as external comb filter are:
longer video path - with everything in between that could worsen the quality instead improve it... like
LD -> cable -> A/D -> DVD digital processing -> D/A -> cable -> capture card
VS
LD -> cable -> capture card
...and the unknown processing inside the DVD recorder... it could include, apart comb filter, video DNR, color DNR, color AGC, MPEG2 conversion, and quite surely TBC, and YUY2 to YV12 conversion. Someone could argue that the latter would be not so bad for quality, but I prefer to stay inside the YUY2 colorspace as long as I can, including color correction and resizing... infact, if I have (for example) 700x340 YUY2 video, the chroma will be (at best) 350x340; useful if I want to convert to 1280x568 - where the chroma resolution will be 640x284; if I have 700x340 YV12, chroma will be only (at best) 350x170... do you think it's still the best option for resizing - also for a "simple" letterbox to anamorphic resize?
I'm also thinking at a "crazy" alternative capture technique... using the LD-V4300D RGB output, capture the separate red, green and blue image, then recover the RGB image with avisynth. I'm sure someone else has done it before, I read it a long time ago, but could not find that technique info again anymore... I know that laserdisc is composite, and the chroma resolution of a PAL laserdisc will be *at best* around 212*576, but who knows how good could be a composite-to-RGB converter inside an old industrial-grade laserdisc player... maybe it will be an interesting discover!
At the end...
Laserdisc captures done; spatio-temporally alignment to median the captures done; upscaling, denoising, sharpening scripts tested - found the best ones; median color correction tested - found good result. Now I must "mix" all these elements, and the video will be ready.
I decided - to reduce processing time, and to not stress a lot my old pc - to process things in distinct steps: tomorrow evening the median/2x upscale will be finished; after that, I'll apply color correction median and then sharpening/denoising/resizing.
Next things to do: capture audio from italian VHS, align PCM, AC3, DTS soundtracks to video, try to find the PAL french laserdisc soundtrack, convert audio to 23.976fps; correct and align the subtitles; convert to suitable release formats; mux all.
Latest news: I decided to buy another PC ("only for Star Wars project?" - "well, *not* only for that...") and it will be... another Sony VGX XL! This time with a faster CPU and a BD BURNER!!! Hope to upgrade soon the 2.13GHz E6400 (no, the Sony VGX-XL series don't permit overclock...) to a faster X6800, or better to a QX6800 - if only I could be absolutely sure it will work into my new PC!
"...do you think anyone will read all your post until here?" (OO_)
(u°°) "...surely someone will read these last lines first!"