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23rd January 2021, 11:31 | #1 | Link |
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How to calculate resize dimensions
When ripping a dvd, I am always confused about the "correct" dimensions for resizing.
Here's what I currently do:
95% of the time my calculated AR and IMDB match. That's what I input into Megui for DAR. However, I never can make sense of the resize dimensions that Megui's avisynth editor comes up with. I'll use The Mask as an example. The source is non-anamorphic, 480p dvd. After ripping, I load the dvi into Megui and change the DAR from itu 16:9 (1.823169) to 1.85. I crop 6 from the top and 12 from the bottom. Megui comes up with a resize dimensions of 720x376 yielding an AR of 1.915 and AR error of -0.37378%. My question is, why not use 720x392 (AR 1.84)? That seems a lot closer to how the movie was shot. For a 1.85 non-anamorphic dvd, shouldn't I always use 720x392? The situation I could see using another resize would be if more than combined 88 pixels cropped from top/bottom (480-88=392) as that would imply "upscaling" the vertical. Obviously the megui author knows a million times more than me regarding video, so I am sure my logic is flawed somehow. I would just like to know how and what is the "correct" way to arrive at a resize given AR and crop. |
23rd January 2021, 15:44 | #2 | Link |
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Really? All DVD sources are anamorphic, i.e. non-square pixel.
Secondly, your very asymmetric top/bottom cropping looks a bit unusual to me for a 1.85 movie. Did you set some 'mod' constraint in your GUI for cropping/resizing? |
24th January 2021, 19:24 | #5 | Link |
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sugargenius,
Your before cropping and after cropping look very similar Is this of any help, [From here:- https://forum.doom9.org/showthread.p...93#post1576193 ] Avisynth Script: Code:
# Based on MEGUI WIKI : http://mewiki.project357.com/wiki/MeGUI/Aspect_Ratio_Signalling_in_AviSynth_Scripts # # SAR=Sample ie pixel Aspect Ratio. FAR=Frame Aspect Ratio (width/height). DAR=Aspect Ratio for Display. ColorBars().ConvertToYV12().Trim(0,300) # 640x480 DAR = 16.0/9.0 # Pretend (FULL FRAME) DAR = 16/9 (Choose your variety of poison) SAR = getSAR(DAR) # Calc SAR, no change when cropping. #Crop(20,20,-20,-20) # We dont want to change DAR here, just testing if MEGUI actually sets 16:9 Aspect ratio correctly. NewDAR = getDAR(SAR) # Calc new DAR after crop and before Resize. DAR no change when resizing. LanczosResize(200,300) # Test to see if MEGUI sets DAR 16:9. (FAR = tall and skinny, MEGUI should set DAR=16:9 ie short and fat) SignalDAR(NewDAR) # Signal DAR to MeGUI : EDIT: Change Name to SignalDAR (From SetDar) return last Function GetDAR(clip c, float SAR) { return Float(c.width) * SAR / Float(c.height)} # Gets the DAR from the SAR Function GetSAR(clip c, float DAR) { return DAR * Float(c.height) / Float(c.width) } # Gets the SAR from the DAR Function SignalDAR(float DAR) { global MeGUI_darx = Round(1000 * DAR) global MeGUI_dary = 1000 } # Signals DAR for MEGUI Code:
DAR = 16.0/9.0 # Pretend (FULL FRAME) DAR = 16/9 (Choose your variety of poison) Code:
SAR = getSAR(DAR) # Calc SAR, no change when cropping. Code:
#Crop(20,20,-20,-20) # We dont want to change DAR here, just testing if MEGUI actually sets 16:9 Aspect ratio correctly. NewDAR = getDAR(SAR) # Calc new DAR after crop and before Resize. DAR no change when resizing. Then get new 'Presentation' DAR as it should be after crop, and used via MeGUI. EDIT: If Interlaced, Can only crop top and bottom in multiples of 4 when YV12, or Multiples of 2 if other colorspace. EDIT: Code:
DAR = FAR * SAR ::: FAR = DAR / SAR ::: SAR = DAR / FAR
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24th January 2021, 23:12 | #6 | Link | |
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Nowadays HDD's are cheap and offer huge capacities!
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25th January 2021, 12:55 | #7 | Link |
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@sugargenius:
Not having seen your source, my best guess from your description would be: 1. The source is "480p DVD" with movie content, hence it is most probably an NTSC DVD with DAR 16:9 2. All DVD video is anamorphic by the DVD standard, there is no "non-anamorphic 480p DVD" 3. As the content seems to be a movie (The Mask) it is most likely progressive video 4. According to IMDB the movie has an aspect ratio of 1.85. Assuming 1. is true, one would expect a frame size of 720x480 with top and bottom black bars of about 10 pixels each. After cropping, the cropped frame without borders has a size of 720x(480-20) = 720x460. It is still anamorphic with a PAR (Pixel Aspect Ratio) of 32:27=1.1852 (or a value close to it, acc. DVD or mpeg2 spec.). 5. 720x460 can be horizontally resized to 854x460 or vertically to 720x388 for square pixels (PAR 1:1) => 854/460=720/388=1.85. Above explains the basic steps (independent of any GUI) based on some assumptions(!) about your source. (MeGUI may round a bit differently due to mod constraints.) For better advice you would have to upload a sample. Last edited by Sharc; 25th January 2021 at 13:14. |
25th January 2021, 13:47 | #8 | Link |
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Here are the url for screenshots. I guess they got stripped out due to my post count?
https://ibb.co/MGQDZMp https://ibb.co/Hg1GBSn |
25th January 2021, 14:29 | #9 | Link |
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It's exactly as I assumed. Nothing unusual. MeGUI just shows the anamorphic source, original and cropped.
Someone who knows MeGUI may chime in and explain how it is supposed to resize with which settings, tickmarks and options ..... |
25th January 2021, 20:18 | #10 | Link | |
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I think you are a bit confused about the DVD standard. Of course DVDs do not use square pixels, but this has nothing to do with anamorphic vs. non-anamorphic. MPEG2 clips can be either flagged as 4:3 (non-anamorphic) or 16:9 (anamorphic). For 16:9 content it makes sense to encode the movie to anamorphic because you do not sacrifice vertical resolution. But for 4:3 content it does not make sense at all to encode it to 16:9 anamorphic. I suggest you take some time to google for "anamorphic vs. non-anamorphic DVDs". |
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25th January 2021, 21:11 | #11 | Link |
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Sharc is correct.
Any image that requires correcting in order for it to be viewed at the proper shape is by virtue...'anamorphic'.
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25th January 2021, 23:10 | #13 | Link |
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Indeed
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25th January 2021, 23:31 | #14 | Link | |
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https://www.pcmag.com/encyclopedia/term/anamorphic-dvd https://en.wikipedia.org/wiki/Anamorphic_widescreen http://thedigitalbits.com/featured/g...d-for-everyone http://invisionsvc.com/Services/Proj...namorphic.html The term "Anamorphic" originates from the anamorphic lenses which were used in film cameras to make it possible to film widescreen movies on traditional 4:3 film material. For DVDs this term has a special meaning, and with the exception of you guys everybody else has agreed on what an anamorphic DVD is. To say that all non-square pixel formats are anamorphic by definition is just ridiculous... |
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25th January 2021, 23:40 | #15 | Link |
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The term 'anamorphic' is not solely related to lenses. It's way older than that!
Anamorphosis...
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Last edited by SeeMoreDigital; 25th January 2021 at 23:42. |
26th January 2021, 02:11 | #16 | Link |
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In this context I always use 'anamorphic' as meaning 'non-square pixels'.
If it is a dichotomy between anamorphic or not anamorphic then this seems like the only useful definition, otherwise how do you describe square pixels?
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26th January 2021, 10:42 | #17 | Link |
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It's the industry that decided to call 16:9 DVDs "Widescreen Anamorphic" to differentiate them from "Full Screen" 4:3 DVDs, which filled the screen when CRTs ruled the world. If the definition of anamorphic is anything with non-square pixels, then they're all anamorphic.
The dictionary definition of anamorphic. https://www.merriam-webster.com/dictionary/anamorphic producing, relating to, or marked by intentional distortion (as by unequal magnification along perpendicular axes) of an image |
26th January 2021, 11:35 | #18 | Link | |||
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Resizing the width up instead of reducing the height for maximum detail. It's mental it's disabled by default. 480 x (16/9) = 853.33 (resized to square pixel dimensions - 853.33 x 480) 853.33 / 460 (after cropping) = 1.85507 There's a very small aspect error when resizing. 852 / 460 = 1.85217 720 / 388 = 1.85567 You can also play with this function. I often crop with MeGUI, then remove MeGUI's cropping from the script and use the same cropping for CropResize. If you specify the correct input DAR for CropResize there can never be any aspect error, as it crops to prevent it if necessary. MeGUI's ITU Input DAR's are possibly a little off. It uses the second lot of ITU (almost exact) pixel aspect ratios in the table I've linked to below as the basis for it's ITU DARs. I create two custom Input DARs of 20:11 and 15:11. They're the mpeg4 DARs. My rule of thumb is always use 15:11 for 4:3 DVDs, 20:11 for older 16:9 DVDs, and 16:9 for newer 16:9 DVDs. This post provides tables of the possible sample/pixel aspect ratios. For the mpeg4 sample/pixel aspect ratios, they work out to a display aspect ratio of 20:11 for both NTSC and PAL 16:9 DVDs, and 15:11 for 4:3 DVDs. The generic pixel/sample aspect ratios give you exactly 16:9 and 4:3. Last edited by hello_hello; 26th January 2021 at 19:25. |
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26th January 2021, 20:02 | #19 | Link | ||
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26th January 2021, 20:14 | #20 | Link | |||
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Last edited by manono; 26th January 2021 at 20:31. |
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