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Low Quality Scaled Image

capella_ben
01 Jan, 2019 05:30
Lately I have noticed that the scaled image you upload is very blury and poor quality.

For examaple on this page:  https://www.astrobin.com/383607/

If I compare with the original image you can really tell the difference:
https://1drv.ms/u/s!AmYsldGbye0hucd5wRsotwGu6gJQog

Why has the image quality gone down?

Many thanks.
capella_ben
02 Jan, 2019 11:07
Looks like it has been reduced in size to 620*411 then expanded in size to about double.

I downloaded it and it look sfine by itself, just a bit too small.

What are the guidelines for the images so we can get them to look good on the page?

Thanks.
siovene
02 Jan, 2019 12:10
Hi Ben,
no, AstroBin does not reduce and then expand again.

Your original upload gets compressed with the following settings:

  • No compression at all for the real-pixels size. AstroBin just adds the watermark if applicable.
  • No compression at all for the HD size, but resized to 1920px wide with 100% JPG quality setting
  • No compression at all for the default view, but resized 620px wide with 100% JPG quality settings
  • Quality reduced to 80% for small thumbnails
I suspect that what you are seeing is that whatever program you are using to view the image on the right of your composition, is also increasing sharpness when displaying the image at a smaller size.

AstroBin prefers not to do any guesses, so it doesn't change anything besides bilinear scaling at maximum quality.
capella_ben
02 Jan, 2019 12:18
Cool, thanks.  I'll have another look at the processing and see if there is something I can do.
capella_ben
13 Apr, 2019 22:48
Salvatore Iovene
Hi Ben,no, AstroBin does not reduce and then expand again.

Salvatore,

After a bit more testing, I have found out what the problem is.  Indeed AstroBin is not expanding out; Windows is.

In windows I have display scaling set to the default of 150% (for my 4K monitor).

In Pixinsight, I can see the image pixel for pixel with my monitor (i.e. it does not apply the scaling).  Here it looks nice and sharp as expected.

However in all my browsers the 150% scaling is applied, so the image is then a little blury.  If I turn off the windows display scaling then all looks sharp, but quite small.

I wonder if there is a way for the AstroBin site to tell the browser to NOT scale an image…
capella_ben
13 Apr, 2019 23:59
I'm no web developer smile , but after a bit of searching, perhaps this link could help.

I'd like to request that the following changes be considered:
  1. The windows scaling be applied to all BUT the image in the astrobin-image-container. This should give us a pixel for pixel display, but will make it image smaller relative to the rest of the page.
  2. Have the image larger than 620 pixels wide IF we are on a 'high resolution' screen.  I guess this may mean you need to keep another scaled copy of the image.
This should then show a crisp image independent of the windows desktop scaling.
 
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