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Test of image resizing

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Post Options Post Options   Quote sybersitizen Quote  Post ReplyReply Direct Link To This Post Topic: Test of image resizing
    Posted: 10 January 2018 at 16:53
Let's do a practical experiment. I'm posting three 16:9 images in different resolutions:

1920x1080:



1280x720:



960x540:



I'm looking at them on a 1920x1080 monitor using Win7, IE11 and also a recent version of Chrome.

I don't see any aspect ratio issues in any of them under any conditions. If you have issues viewing them, what are you seeing, and what exactly is it that you want to see instead? What hardware/OS/browsers are you using?
 



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Post Options Post Options   Quote QuietOC Quote  Post ReplyReply Direct Link To This Post Posted: 10 January 2018 at 17:10
They look fine on a Chrome window maximized on a 1280x1024 monitor in Windows 7. The first two look to be identical and the third is slightly smaller. No horizontal scroll bar. Zooming to 200% shows much more detail in the top image while the bottom image just becomes heavily aliased. The middle image is less aliased at 200% than the bottom, but clearly has less detail than the top image.

On my Samsung Note 4 1920x1080 AMOLED in Chrome (mobile default) all three look identical and fill the full display width even in landscape orientation--no horizontal scroll bar. Pinch zooming in there is much more detail in the top image while the bottom image just becomes heavily aliased.

Note 4 Chrome on Desktop Site has same behavior as Chrome on Windows 10.

Edited by QuietOC - 10 January 2018 at 17:28
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Post Options Post Options   Quote bms44974 Quote  Post ReplyReply Direct Link To This Post Posted: 10 January 2018 at 17:15
no problems on IE11 (view scaled to 250%) with 4K display.

Cheers... Brian

P.S. Same result... first 2 look the same and third is slightly smaller (no horizontal scroll bar)
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Post Options Post Options   Quote pegelli Quote  Post ReplyReply Direct Link To This Post Posted: 10 January 2018 at 17:15
Looks perfectly fine to me, thanks for repeating the test here
Mind the bandwidth of others, don't link pictures larger then 1024 wide or 960 pix high, see here
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Post Options Post Options   Quote sybersitizen Quote  Post ReplyReply Direct Link To This Post Posted: 10 January 2018 at 17:45
Originally posted by QuietOC QuietOC wrote:

The first two look to be identical and the third is slightly smaller. No horizontal scroll bar. Zooming to 200% shows much more detail in the top image while the bottom image just becomes heavily aliased. The middle image is less aliased at 200% than the bottom, but clearly has less detail than the top image.

Yes, there should be only two differences among them as they are seen here in the forum.

1. The first two are resized by your browser to the dyxum limits while the third gets no resizing at all.

2. Because the first two have been resized on the fly, the possibility of visible aliasing exists. This shows up mostly in the upper region of the image. On my monitor, the first image has the worst aliasing; the second is not too bad.

If your browser allows you to also view them outside of dyxum, then you should see them at their full resolutions and without any aliasing.
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Post Options Post Options   Quote QuietOC Quote  Post ReplyReply Direct Link To This Post Posted: 10 January 2018 at 18:03
Syber,

I am viewing the images in the Dyxum forum. I am using the zoom option in Chrome.

I don't see aliasing in the top two images at the default 100%.

I am saying when I use the zoom control in the browser to go to 200% the bottom image becomes pixelated (or aliased). It has been expanded to 2:1.

The Dyxum code that scales large images to 1024 pixels doesn't force a 1:1 pixel mapping. it just sets the image width to be 1024 pixels at 100% zoom. At 200% zoom the image is now 2048 pixels wide and if it has 2048 pixels it will be at 1:1 on the display.

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Post Options Post Options   Quote Bob J Quote  Post ReplyReply Direct Link To This Post Posted: 10 January 2018 at 19:47
I'm using Firefox on a two monitor HD portrait/landscape PC system.

The first two appear the same size on the landscape monitor (which will be 1024 wide). On the portrait monitor, the smallest resolution just goes off the edge of the screen. I'm guessing that maybe about 900 width would fit on a portrait HD monitor without the scroll-bars.
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Post Options Post Options   Quote sybersitizen Quote  Post ReplyReply Direct Link To This Post Posted: 10 January 2018 at 20:31
Originally posted by QuietOC QuietOC wrote:

I am viewing the images in the Dyxum forum. I am using the zoom option in Chrome.

I don't see aliasing in the top two images at the default 100%.

So you are in fact looking at the entire post with all three images? I don't know why you aren't seeing what I see.

When I do that using Chrome and look at the upper left corners, I can see noticeable aliasing in the first image, not much at all in the second (because the downsampling ratio is different), and none in the third (because that one has not been downsampled for display at all). Here is a composite screen grab of the three upper left corners:



This is not unexpected, BTW. Downsampling on the fly can often cause it.

I am saying when I use the zoom control in the browser to go to 200% the bottom image becomes pixelated (or aliased). It has been expanded to 2:1.

Yes, as expected. The browser is just magnifying each image pixel to occupy more screen pixels.

The Dyxum code that scales large images to 1024 pixels doesn't force a 1:1 pixel mapping. it just sets the image width to be 1024 pixels at 100% zoom.

As MiPr explained in the other thread, that actually happens within the browser through its own downsampling algorithm.

At 200% zoom the image is now 2048 pixels wide and if it has 2048 pixels it will be at 1:1 on the display.

Yes, as expected.
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Post Options Post Options   Quote sybersitizen Quote  Post ReplyReply Direct Link To This Post Posted: 10 January 2018 at 23:41
Originally posted by sybersitizen sybersitizen wrote:

Originally posted by QuietOC QuietOC wrote:

I am viewing the images in the Dyxum forum. I am using the zoom option in Chrome ... At 200% zoom the image is now 2048 pixels wide and if it has 2048 pixels it will be at 1:1 on the display.

Yes, as expected.

Actually, I wonder if there might be a difference between using the zoom feature in Chrome (or IE11) while within dyxum vs. viewing the image in a browser outside of dyxum at its full resolution.

In 200% zoom mode, the browser might only be upsampling the image seen within dyxum, which spreads the data in one image pixel across multiple screen pixels; but a separate browser window for the image by itself can map each individual image pixel to an individual screen pixel.

The difference might be subtle, but it should be visible if there is one. Here I'm posting another version of that image at a resolution of 2048x1152. Within the dyxum post it should display at 1024x576. Look at that using your browser of choice at 200% and carefully compare it to a separate browser window with just the image itself at 100%.

2048x1152:



Later: Both methods seem to look the same in Chrome. Testing IE11 next.

Later still: Okay, much the same story with IE.

But either way, with an image of that resolution, I wouldn't want to use the 200% zoom option because I can only see a portion of it at a time with my 1920x1080 monitor, and a big scroll bar appears. The separate window for the image file by itself is the way I'd go.

Edited by sybersitizen - 11 January 2018 at 00:25
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Post Options Post Options   Quote QuietOC Quote  Post ReplyReply Direct Link To This Post Posted: 11 January 2018 at 03:06
Syber,

I can see the whole width of that image at 200% on my 2560x1080 monitor. It looks like it is 1:1 on the Dyxum page. It looks good. Just the same as viewing the image at 100% by itself in its own tab/window in Chrome.
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Post Options Post Options   Quote sybersitizen Quote  Post ReplyReply Direct Link To This Post Posted: 11 January 2018 at 03:17
Originally posted by QuietOC QuietOC wrote:

I can see the whole width of that image at 200% on my 2560x1080 monitor.

Ah - you didn't mention your monitor resolution earlier.

It looks like it is 1:1 on the Dyxum page. It looks good. Just the same as viewing the image at 100% by itself in its own tab/window in Chrome.

Yes, I agree with that.
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Post Options Post Options   Quote Miranda F Quote  Post ReplyReply Direct Link To This Post Posted: 11 January 2018 at 13:19
Originally posted by QuietOC QuietOC wrote:

They look fine on a Chrome window maximized on a 1280x1024 monitor in Windows 7. The first two look to be identical and the third is slightly smaller. No horizontal scroll bar. Zooming to 200% shows much more detail in the top image while the bottom image just becomes heavily aliased. The middle image is less aliased at 200% than the bottom, but clearly has less detail than the top image.

On my Samsung Note 4 1920x1080 AMOLED in Chrome (mobile default) all three look identical and fill the full display width even in landscape orientation--no horizontal scroll bar. Pinch zooming in there is much more detail in the top image while the bottom image just becomes heavily aliased.

Note 4 Chrome on Desktop Site has same behavior as Chrome on Windows 10.


Dito for me, Chrome on win7 with 1920 x 1080 monitor, and also as QuietOC says for the mobile version on my Nokia win 8.1

I hadn't realised that Dyxum automatically resized pictures. I've been doing that manually before generating the link.
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Post Options Post Options   Quote Miranda F Quote  Post ReplyReply Direct Link To This Post Posted: 11 January 2018 at 13:21
Originally posted by sybersitizen sybersitizen wrote:


If your browser allows you to also view them outside of dyxum, then you should see them at their full resolutions and without any aliasing.


Doesn't work that way for me on Chrome / win7. Opening the image in a new tab copies the Dyxum size (ie, choosing 100% shows it the same size). Except that I can zoom in a long way before I see pixellation, and inspecting the source shows the image to be the size claimed, so I am guessing that opening the image again keeps the '100% display size' unchanged while maintaining the full image.

Edited by Miranda F - 11 January 2018 at 13:27
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Post Options Post Options   Quote sybersitizen Quote  Post ReplyReply Direct Link To This Post Posted: 11 January 2018 at 15:57
Originally posted by Miranda F Miranda F wrote:

Originally posted by sybersitizen sybersitizen wrote:


If your browser allows you to also view them outside of dyxum, then you should see them at their full resolutions and without any aliasing.

Doesn't work that way for me on Chrome / win7. Opening the image in a new tab copies the Dyxum size (ie, choosing 100% shows it the same size).

I'm talking about right-clicking on the image and selecting 'Open image in new tab', then looking at that tab.

You can then press F11 to get a full screen view; depending on the image resolution, you might also have to click that image to get 1:1 pixel magnification.
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