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Aspect Ratio & Native Resolution


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38 replies to this topic

#21 OFFLINE   georgemartin601

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Posted 26 March 2011 - 08:26 AM

Haven't been able to put anything to the test yet, but all sounds like very good relevant info . . . thanks to everyone.

If this helps, here's my equipment:

- Panasonic TC-P54VT25 Plasma
- DirecTV HR24-100 (& H24-200)
- Not really relevant - Panny bluray and sound

Sounds like everyone knows what I'm after and I'm probably trying to simplify something that really isn't simple at all. I'll re-state my goal based on the above info - I want to do as little content altering as possible, unless the altering can actually provide a better picture while maintaining the original aspect ratio.

I'm going to start by testing with Native On, Format Original, and Pillarbox and have my TV use the Full picture setting.

Thanks much to all

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#22 OFFLINE   veryoldschool

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Posted 26 March 2011 - 09:41 AM

Haven't been able to put anything to the test yet, but all sounds like very good relevant info . . . thanks to everyone.

If this helps, here's my equipment:

- Panasonic TC-P54VT25 Plasma
- DirecTV HR24-100 (& H24-200)
- Not really relevant - Panny bluray and sound

Sounds like everyone knows what I'm after and I'm probably trying to simplify something that really isn't simple at all. I'll re-state my goal based on the above info - I want to do as little content altering as possible, unless the altering can actually provide a better picture while maintaining the original aspect ratio.

I'm going to start by testing with Native On, Format Original, and Pillarbox and have my TV use the Full picture setting.

Thanks much to all

With HD, there is either no scaling or very little [720p needs some for a 1080 display], so SD should really be the only one that this would be noticeable.
Perhaps the thing to do is to turn native off and then select an SD channel that is showing a show in 16:9, where it has boarders on all sides.
With native off, the format button will cycle through all formats & resolutions. This will show how well the receiver scales, as you cycle through them.
Then I'd stop with the receiver on 480i/p and original format, and use the TV remote to change the TV format to zoom.
This will have the TV doing the most scaling.
Compare the TV scaling and the receiver with crop should give you the best idea of which works better, if there is a difference.
Some can't see any, while others can. The receivers are the same so this comes down to whether the TV is better at this or not.
A.K.A VOS

#23 OFFLINE   BattleZone

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Posted 26 March 2011 - 09:56 AM

Okay, your Panasonic has a 1920x1080 panel. The ONLY signals that will not need to be scaled are "1080" source signals. All signals that are either "480" (720x480) or "720" (1280x720) MUST be scaled up by either the TV set or the DVR if they are to fit the screen. Without scaling, SD signals (480) would be postage-stamp sized in the middle of your TV screen with huge black bars on all sides.

So, you have to figure out which scaler does a better job: the one in the TV set, or the one in the DVR. If the DVR is set to "Native: On", then the TV set is doing the scaling. If "Native: Off", then the DVR is doing the scaling.

For SD content, "Pillar Box" is what will give you the "most correct" aspect ratio. MOST TVs can't handle "original" format SD signals automatically, so you'd need to "ride" your TV's "format" or "aspect ratio" button as you changed channels in that mode.

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#24 OFFLINE   veryoldschool

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Posted 26 March 2011 - 10:06 AM

For SD content, "Pillar Box" is what will give you the "most correct" aspect ratio. MOST TVs can't handle "original" format SD signals automatically, so you'd need to "ride" your TV's "format" or "aspect ratio" button as you changed channels in that mode.

You see many more TVs than I do, so this may be true, "but" the TVs that I've have/had, a setting for 4:3 480.
"for instance", I set my Sony for zoom with 4:3. The windowboxed SD programing has me change the receiver to original and the TV zooms it. After I'm done watching, I change the receiver to pillarbox, and the TV changes from zoom to full, which is the 16:9 setting for it.
This means I only need one remote and just a few presses of format to cycle into and out of the TV's zoom mode.
A.K.A VOS

#25 OFFLINE   TomCat

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Posted 27 March 2011 - 12:44 AM

...Compare the TV scaling and the receiver with crop should give you the best idea of which works better, if there is a difference.
Some can't see any, while others can. The receivers are the same so this comes down to whether the TV is better at this or not.

Some may think they can see a difference, but that is only because they think they can. The differences between modern scalers are virtually negligible. They all use the same algorithm to do the job. Human vision, even from golden trained eyeballs, is as incapable of seeing the difference as humans are of following a scent trail like a bloodhound. Bloodhounds, like sharks, have finely developed senses. We don't.

We are simply not equipped to distinguish the difference, which is also why we can regularly compress HD video 100:1 before it begins to become noticeable. There has never been anyone who could distinguish scaling artifacts from modern scalers in a double-blind study. In fact, no one can really look at video and tell you if it is 1080i or 720p, either. Well, they maybe can tell you, but they don't really know, even if they think they do.

Much more visible (and still mostly not noticeable) are deinterlace errors. Pre-2005 sets often did not do this well (which is why deinterlace in the DVR may be better for them). Even that cheap Vizio doesn't deinterlace all that well; the one I am familiar with does it well 99.99% of the time, but certain sorts of motion or picture changes will make it burp and line dice noticeably for a split second. And it is not the smooth normal interlace artifacts you see on motion, it varies very widely and quickly; perfect for a split second, widely line-diced for the next, which is annoying.

Bottom line, it is worth experimenting to see whether the DVR or TV itself does a better job of both, even though the scaling is rarely if ever different for modern sets. Sadly, deinterlace is not so ubiquitously perfect.

+++++++++++++++++++++++++++++++++++++++++++

But I digress. Back to scaling. Scaling is very simple math, done very quickly: For instance, to scale 1080 to 720, if you overlay the pixel grid map of 1280x720 over the pixel map of 1920x1080, you can see and measure exactly where each 720 pixel falls in physical relationship to teach 1080 pixel. Only four pixels on the source map are relevant to each new pixel location. Assuming you were trying to find just the new value in the H dimension, if the first 720-map pixel of line 1 falls 66.67% on pixel 1 and 33.33% on pixel 2 of line 1 of the 1080 map, then you can multiply the binary coefficient representing the first pixel on the 1080 map by 0.666, and the second value (of the second pixel) by 0.333, then add the two together.

That gives the value that the first 720-map pixel should be in the H dimension, which is somewhat of an average of what the luminance would be on the 1080 map at that 720 map pixel's physical location for the two 1080 pixels that "share", or more accurately are adjacent to that same point of real estate. Of course you have to do this in the vertical dimension as well, so actually four pixels and four constants are involved in calculating each new pixel value for every pixel, two in the H dimension and two in the V dimension. That is basic math a fourth grader can understand.

There is rounding involved, but it is negligible; at the worst case, since there are 219 possible values for luminance in 8 bit 4:2:0, the error would be less than half of one IRE in brightness (in analog terms) which is not distinguishable at any grey level, and the error is on average half that (the rounding drags the calculated value either to the quantum level above or below it, whichever is closer). For scaling between 480, 720, 768, and 1080, the rounding errors are even much lower than that; often there is no rounding error at all for most pixels, meaning the scaling is completely or at least virtually transparent. Certainly not even approaching visible.

If there would be rounding (which really only exists in scaling done between uncommon formats) it could result in banding, but nearly or totally invisible banding. If you see banding it is due to compression, not scaling, because that sort of artifact is much more severe when compression is high (as it is for ATSC, DVB, and QAM delivered to consumers), and common scaling has very little rounding errors. Oversampling could eliminate the errors, but is not needed since there really are no visible errors when scaling common formats in the first place.

Since the map never changes, the values of those multipliers are constants, That means they can be written into the formula, burned into the silicon as a lookup table, and do not have to be recomputed each time. And since pixels for 720p, for example, are 1.5 times as wide and 1.5 times as tall as 1080p pixels, there are only three constants needed, 4, 2, and 1 (so really, just two, as the 1 can be ignored and 2 is used twice). Since the math is done in integers this reduces the rounding error possibility to almost zero.

If you look at the attached diagram, it shows the first 5 pixels of the first 3 lines of the 1080 luminance pixel map in black and white. Overlayed over that is the first 3 pixels of the first 2 lines of the 720 pixel map, in blue. Note that this represents the top-left corner of an HD display.

To calculate the luminance value of pixel 1 line 1 of the 720 map, take the luminance value of pixel 1 line 1 of the 1080 map and multiply it by 4. Take the value of pixel 2 line 1 of the 1080 map and multiply it by 2. Take the value of pixel 1 line 2 of the 1080 map and multiply it by 2. Take the value of pixel 2 line 2 of the 1080 map and multiply it by 1 (simply use the whole value of pixel 2 line 2 in this case).

Notice that these constants directly represent the amount of area (divided by 9) that the new 720 pixel overlays for each of the four 1080 pixels (each 720 pixel always overlays either 4/9ths, 2/9ths, or 1/9th of each corresponding 1080 pixel).

Add these four new values (the binary coefficients representing the 1080 pixel times their constants) together and divide by 9, and that gives the luminance value to assign to the new 720 pixel, for line 1 row 1. Now repeat the process for each remaining 720 pixel.

Congratulations, you have just rescaled 1080p to 720p.

Thats a total of 6 (really 5) simple calculations per pixel: multiply each of the coefficients representing 4 pixels (those from the source map overlayed or adjacent to the new pixel location on the target or destination pixel map) by its lookup table constant, add those values together then divide by 9 to resolve each new coefficient representing each new pixel (the "9" is where the tiny amount of rounding error creeps in).

Now that we have what is a very simple formula, all we have to do is crunch the numbers of the new pixels fast enough, which even for for 1080p60 is just over 18 million calculations per field, (12+ million for luminance, 3+ mill for Cr, and 3+ mill for Cb) or just over 1 billion calcs per second, give or take, even including the phantom 6th calculation, a speed any modern dedicated microprocessor can handle without even breathing hard. Resolutions lower than 1080p60 are even easier, because there are fewer pixels, meaning fewer calcs per second.

Attached Thumbnails

  • pixel map scaling.png

Edited by TomCat, 27 March 2011 - 05:09 AM.

It's usually safe to talk honestly and openly with people because they typically are not really listening anyway.

#26 OFFLINE   HoTat2

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Posted 27 March 2011 - 06:01 AM

Hey, all these responses are very interesting;

But to simplify matters a lot, I think the OP's problem is that unless there's something screwy going on with the equipment. With native on and all resolutions checked and format on original unaltered, the receiver should be outputting a 4:3 signal on SD channels and 16x9 on the HD ones. Therefore his TV should be set to 4:3 mode when receiving SD channels and generate the necessary pillar bars.

The wide or 16x9 TV setting should only be for the HD channels. After which the TV should then memorize both these settings.

At least this is the way all my Samsung LCDs are configured with native on and all resolutions checked and format on original/unaltered.

IOW, it sounds like the OP's TV is just incorrectly set to wide/16:9 when viewing 4:3 channels which will result in a full screen stretch-o-vision display.

#27 OFFLINE   georgemartin601

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Posted 27 March 2011 - 07:35 AM

Watched some tube last night. Native On, Format Original, Pillarbox On, TV set to Full Aspect Ratio. *This TV's Full Aspect setting means (in very very short terms) it will not alter the aspect ratio of the signal it is sent. Everything looks good and meets my needs. 4x3 content is displayed with bars on both sides. And as others have already stated, the Pillarbox setting has no effect on HD source content, so switching back to HD broadcasts does not require a change anywhere.

I experimented with allowing the TV to do the 4x3 setting. Although I didn't notice a change in picture quality, it did require me to set the Aspect back to Full when switching to HD broadcasts. So the decision was made for me, essentially.

I think I've gained an understanding about the things I originally had issue with, that is, why DirecTV uses terms like "original". I'd LIKE to say I understood every post in this thread to its full extent. But some of you are *sick! Thanks very much to all.

*sick = cool as sh!t/knowledgeable

#28 OFFLINE   BattleScott

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Posted 27 March 2011 - 08:28 AM

Watched some tube last night. Native On, Format Original, Pillarbox On, TV set to Full Aspect Ratio. *This TV's Full Aspect setting means (in very very short terms) it will not alter the aspect ratio of the signal it is sent. Everything looks good and meets my needs. 4x3 content is displayed with bars on both sides. And as others have already stated, the Pillarbox setting has no effect on HD source content, so switching back to HD broadcasts does not require a change anywhere.

I experimented with allowing the TV to do the 4x3 setting. Although I didn't notice a change in picture quality, it did require me to set the Aspect back to Full when switching to HD broadcasts. So the decision was made for me, essentially.

I think I've gained an understanding about the things I originally had issue with, that is, why DirecTV uses terms like "original". I'd LIKE to say I understood every post in this thread to its full extent. But some of you are *sick! Thanks very much to all.

*sick = cool as sh!t/knowledgeable


Bolded items are one or the other and this is where the difference comes from. As BattleZone (no relation :D) said earlier, many TVs (especially Pannasonic) don't recognize the aspect flag in an SD video stream so the "full" mode treats them as 16:9 when the receiver is set for "original format". By setting the receiver to "pillar box", the receiver (which does recognize the SD flag) inserts the pillar box sides so the tv displays the image correctly even though it is still displaying a 16:9 SD image.

The term "original format" is exactly correct as far as the receiver is concerned because it is doing just that, outputting the video stream without change. The issue comes in because the TV (my pannasonic is the same way) doesn't recognize the aspect ratio flag and treats the signal as 16:9 by default.

To illustrate what is acutally happening, set the TV to display gray pillar boxes and set the receiver to display black bars, then select an SD channel to view.

1 - select "original format" on the receiver and put the TV in 4:3, the pillar boxes will be gray showing that it is being done by the TV.

2 - put the TV back to FULL and the image will change to the 16:9 stetched appearance.

3 - with the TV set to FULL, select "pillar box" on the DTV receiver (format button on the remote), the image will now display as 4:3 but the pillar bars will be black showing that the receiver is inserting them and the TV is really still displaying as a 16:9 image (or the bars would be gray).
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#29 OFFLINE   georgemartin601

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Posted 27 March 2011 - 08:43 AM

Battlescot - yep, I'd agree with all of that. I should have distinguished "Format" better. I'm referring to the Format option within the DVR's HDTV Menu setting, where one can choose "Original", as opposed to the Signal+Original that you'd set by hitting the Format button on the remote.

Nevermind above, just double-checked. It does indeed switch the format within the HDTV menu when switching at the remote button level.

Edited by georgemartin601, 27 March 2011 - 08:47 AM.
Obviously still confused, but can't argue with success


#30 OFFLINE   BattleScott

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Posted 27 March 2011 - 09:15 AM

Battlescot - yep, I'd agree with all of that. I should have distinguished "Format" better. I'm referring to the Format option within the DVR's HDTV Menu setting, where one can choose "Original", as opposed to the Signal+Original that you'd set by hitting the Format button on the remote.

Nevermind above, just double-checked. It does indeed switch the format within the HDTV menu when switching at the remote button level.


Correct, you are changing the same setting either way. Another tip for the format button, you can toggle the native mode by holding the format button down for 3 secs. There won't be any visible sign that anything changed (except in the menu screen), but it does change.
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#31 OFFLINE   HoTat2

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Posted 27 March 2011 - 10:22 AM

Hey interesting;

And my apologies too, as I assumed it was standard for all modern flat panels to recognize the aspect ratio flag and default to 4:3 for SD signals and 16:9 for HD ones.

I also guess I sort of lucked out then by choosing a manufacturer who's sets (Samsung in this case) seem to regularly recognize the flag. :hurah: Since it has been my experience that the pillar-box setting on my HR2Xs slightly over squeezes an SD signal stretched to 16x9 resulting in a slight "Stan Laurel" effect for objects in the image.

Therefore letting the TV set handle the pillar-boxing for SD channels really works best for me.

#32 OFFLINE   veryoldschool

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Posted 27 March 2011 - 10:30 AM

Some may think they can see a difference, but that is only because they think they can. The differences between modern scalers are virtually negligible.

I don't know why you do this. :nono:
Comparing my Sony XBR 2 scaler to the DirecTV receivers show a quite noticeable difference when in zoom/crop mode, where the most scaling is being done.
Maybe you should "walk a mile in someone's shoes" before you tell them how they should feel.
Anytime you want to stop by and see this for yourself, "just let me know". :)
A.K.A VOS

#33 OFFLINE   veryoldschool

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Posted 27 March 2011 - 10:35 AM

Hey interesting;

And my apologies too, as I assumed it was standard for all modern flat panels to recognize the aspect ratio flag and default to 4:3 for SD signals and 16:9 for HD ones.

I also guess I sort of lucked out then by choosing a manufacturer who's sets (Samsung in this case) seem to regularly recognize the flag. :hurah: Since it has been my experience that the pillar-box setting on my HR2Xs slightly over squeezes an SD signal stretched to 16x9 resulting in a slight "Stan Laurel" effect for objects in the image.

Therefore letting the TV set handle the pillar-boxing for SD channels really works best for me.

The bold part is where all of these setting really come down to.
Everyone has slightly different equipment and views, so these settings will vary for each of us.
Finding what works best for you, is the "right thing", for you. :)
A.K.A VOS

#34 OFFLINE   HoTat2

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Posted 27 March 2011 - 11:23 AM

I don't know why you do this. :nono:
Comparing my Sony XBR 2 scaler to the DirecTV receivers show a quite noticeable difference when in zoom/crop mode, where the most scaling is being done.
Maybe you should "walk a mile in someone's shoes" before you tell them how they should feel.
Anytime you want to stop by and see this for yourself, "just let me know". :)


While I certainly liked TomCat's explanation of the scaling process, I have to agree VOS. For instance unless there is some sort of defect in the DVR's scaler or some other, when I tried setting my brother's HR22-100 to scale all channels to 1080i hoping to alleviate the HDMI re-syncing delay he hates whenever changing between SD and HD channels, the PQ was very poor. So I had to leave his DVR on native and let his TV handle all scaling and for him to just have to live with the syncing delay.

The only thing I question about your method VOS is that while this may work fine when the SD picture in 16:9 letterbox. When you zoom a full 4:3 image which most SD programs are in, aren't you cutting off some of the top and bottom portions of the image?

#35 OFFLINE   veryoldschool

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Posted 27 March 2011 - 11:46 AM

The only thing I question about your method VOS is that while this may work fine when the SD picture in 16:9 letterbox. When you zoom a full 4:3 image which most SD programs are in, aren't you cutting off some of the top and bottom portions of the image?

I toggle between pillarbar & original on SD programing.
Native on, so the TV is still scaling SD, but when I want to fill the screen with the SD 16:9, I select original, with the TV set to zoom 4:3. After finishing the show, I toggle back to pillarbar, which has the 16:9 flag, so the TV switches back to full.
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#36 OFFLINE   HoTat2

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Posted 27 March 2011 - 11:57 AM

I toggle between pillarbar & original on SD programing.
Native on, so the TV is still scaling SD, but when I want to fill the screen with the SD 16:9, I select original, with the TV set to zoom 4:3. After finishing the show, I toggle back to pillarbar, which has the 16:9 flag, so the TV switches back to full.


I understand that, but when you zoom in on a "full" 4:3 image (that is no letterboxing or matte bars at the top or botom) doesn't that result in cutting off some the picture at the top and bottom?

#37 OFFLINE   veryoldschool

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Posted 27 March 2011 - 12:33 PM

I understand that, but when you zoom in on a "full" 4:3 image (that is no letterboxing or matte bars at the top or botom) doesn't that result in cutting off some the picture at the top and bottom?

Right. If the SD image is 4:3, then crop/zoom will cutoff the top & bottom.
I use this for SD 16:9, which will have both letterbox & pillarbars, or "windowbox".

Here are two screen shots with zoom [from my TV] and crop [from my receiver]:

P0003164.JPG

P0003166.JPG


[edit] Just for another data point for Tomcat [since I don't want to repeat the last time he didn't agree with me] I showed an 87 year old great grandmother the TV zoom and the receiver crop screens, and she could tell the differences from 4+ feet away.

Edited by veryoldschool, 27 March 2011 - 12:49 PM.

A.K.A VOS

#38 OFFLINE   TomCat

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Posted 28 March 2011 - 07:41 PM

My post was about scaling one standard format to another, and it had nothing in it about cropping a format or zooming a format. That is a side issue I did not see a reason to address. The point was that when rescaling between 720p, 480i/p, 768p, and 1080i/p, which are the standard formats a display has to rescale between, for instance, to allow a 1080p TV to display 720p content, the math is simple and the rounding errors are negligible. And everything I posted still stands, and I still support it 100%.

That post was specifically in response to the question raised as to the importance of where the user rescales (in the DVR or in the display) only, the answer being that as far as rescaling itself is concerned (and not deinterlace, crop, and zoom issues at all) it really does not matter, specifically because modern rescalers are ubiquitously the same, and virtually equally transparent. And that is not an opinion; for those who could take the time or have the mental wherewithall to stay with it for long enough the reason why was explained by example in excruciating detail. With diagrams, no less. Was I just wasting my time by trying to illustrate the point?

Part of the design choices made by the ATSC committee when considering 1080 and 720 as new formats were exactly because the scaling math to get between them or to legacy 480 would be simple and transparent. 768 just happens to be another number that fits those same parameters, so for a time, 768-native sets were sold, and they also had transparent scaling.

Cropping and zooming 4:3 to 16:9 is quite different. The ATSC recognized this might be an issue that would inform what the new aspect ratio should be, but rightly assumed that cropping and scaling was not something that could practically yield acceptable pictures anyway, so they opted to not hold it in high importance when deciding what the new aspect ratio would be; other reasons were much more important in coming up with 16:9 beyond whether cropping and zooming between them would be viewable. Rescaling is involved, but the math is not as simple and the rounding errors may therefore indeed be visible. Who among us has ever seen 4:3 zoomed to 16:9, or vice versa, that looked good, for instance?

Not only that, but different algorithms exist which may not be equally effective, making where the crop or zoom happens an issue. Rescaling for ATSC formats is spelled out quite literally regarding how consumer STBs must do it, and they all do it the same way, partly for that reason, and partly because there is no better way to do it. Cropping and zooming, on the other hand, is beyond the scope of the ATSC rules and is completely up to the display/DVR manufacturer as to how they want to go about doing that. Some may actually opt to do it in the analog domain. That can be cheap but it sure can't be pretty. What is surprising to me and possibly to the ATSC committee members themselves is that they attempt to do it at all, as it seems to have no real value beyond filling the screen at the expense of grossly distorting the video.

I thought it was actually quite clear what I was talking about, and that it should go without saying that when a person talks about one thing that does not mean that they are talking about something else, but apparently that is often not clear enough nor obvious enough for those who have difficulty paying attention.

No one should be surprised that cropping and zooming doesn't yield video as good as standard scaling between standard formats. And no one should be surprised that when doing standard rescaling from a lower resolution format (i. e. 480i) to a higher resolution format, that the effective resolution does not improve. Only when scaling down to a lower resolution format does the target resolution match the target format.

Edited by TomCat, 28 March 2011 - 07:59 PM.

It's usually safe to talk honestly and openly with people because they typically are not really listening anyway.

#39 OFFLINE   veryoldschool

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Posted 28 March 2011 - 08:13 PM

Who among us has ever seen 4:3 zoomed to 16:9, or vice versa, that looked good, for instance?

"Well" I for one, can zoom an SD letterbox to fit my display and have it look "fairly good".
Scaling down should be a no brainer, since detail/bits are being dropped.
Scaling up from 1280x720 to 1920x1080, isn't that much and I [too] doubt anyone could tell. SD is where the most scaling is needed, so this would show it.
Pushing this farther to zoom/crop can show a difference as the screen shots show. Can't say that nobody couldn't tell. :nono:
Since we're living in a transition still between 16:9 programing and SD channels, "zoom/crop" still has a function, unless one likes postage stamp viewing.
A.K.A VOS




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