Lossless, Lossy and Avatars

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BobH
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Lossless, Lossy and Avatars

Post by BobH »

After reading this article so kindly presented by Rudi, I think I finally understand why I've had problems turning pics into avatars. When I've tried to make avatars from pics, they always lost sharpness. This makes sense to me now.

Most pics I make are done with my iPhone 6. It makes some truly good pics compared to my old 4S but it still records them as JPEG files, a lossy format. In order to get the file sizes small enough and the pixel dimensions small enough, I crop the pics reducing file size but that doesn't always get the files small enough. Usually, to meet the pixel dimension limit, a photo based avatar loses so many data points that sharpness is greatly reduced.

I've noticed that many of avatars that I see that appear the sharpest are graphics based, not photo based. I guess that graphics are more consistent in color range requiring fewer data points to capture the image. Fewer data points equals smaller file sizes.

Are these observations consistent with the How-to-Geek article?
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Rudi
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Re: Lossless, Lossy and Avatars

Post by Rudi »

Hi Bob,

Your analysis is 100%.

iPhones currently save photos in Hi Quality JPG format, and screenshots are saved in PNG format. Since the photo (in JPG) is the original image, even though JPG is a lossy format, you will not end up with a degraded image (since it is the original). Only when you start editing and saving it from that point will the image start degrading further. (Like the article mentions; photocopies from the original).

Regarding your avatars, if you can crop the image ONLY (iow, retaining the 100% ration of pixels), the image will stay sharp. It is only when you start editing the pixel ratio (using the slider bar in a graphics editor to reduce the file size) where the image will become more degraded. Avoiding the slider will keep your avatars quite clear. If the slider cannot be avoided due to avatar size limitations, then you'll need to bribe the Admins with gifts, money or praise, LOL/Wink!

Your last paragraph starting with "I've noticed..." is 100% accurate.

BTW:
Here are some additional reads to further clarify image quality and format wrt the iPhone 6.

-- What you need to know about shooting raw images on your phone (note: iPhones cannot shoot in RAW, yet!)
-- Getting maximum from your iPhone camera: RAW and TIFF vs JPEG
-- Why Your iPhone Uses PNG for Screen Shots and JPG for Photos
-- Using JPEG and TIFF File Formats in iPhone Photography
Regards,
Rudi

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BobH
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Re: Lossless, Lossy and Avatars

Post by BobH »

Thanks, Rudi!

Can you explain what (generally) happens during a Resize operation to the sharpness of an image file? I can wrap my wee brain about what happens if I crop an image; the file MUST bet smaller; but what happens if I don't change the content but only the horizontal and vertical dimensions? My guess is that whatever software does this is tossing out data points; ergo the file is smaller, and, if enlarged again, will be less sharp for having lost the data points.

Am I in the right city (never mind the right ballpark)?
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BobH
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Re: Lossless, Lossy and Avatars

Post by BobH »

Thanks, Rudi!

Can you explain what (generally) happens during a Resize operation to the sharpness of an image file? I can wrap my wee brain about what happens if I crop an image - the file MUST get smaller - but does it lose sharpness? What happens if the content is unchanged but the horizontal and/or vertical dimensions are reduced? My guess is that whatever software does this is tossing out data points; ergo the file is smaller, and, if enlarged again, will be less sharp for having lost the data points. Is this process done to an industry standard or is it up to the software house to choose its own algorithm?

Am I in the right city (never mind the right ballpark)?
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HansV
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Re: Lossless, Lossy and Avatars

Post by HansV »

There are several algorithms for resizing a picture. Some graphics programs give you a choice. For example in FastStone Image Viewer:
S0742.png
Some filters (algorithms) will produce a sharper image, others will be faster.

The relative size also matters: say you have a 1280 x 960 pixels image. If you reduce it to 640 x 480, you could leave out every other pixel horizontally and vertically, or you could average the color of every 2 x 2 pixel block. That is relatively straightforward. But if you want to reduce it to for example 78 x 58, it's more complicated - there is no easy ratio from 1280 to 78, and whatever method you choose, you'll lose a LOT of detail.
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Rudi
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Re: Lossless, Lossy and Avatars

Post by Rudi »

Hi Bob,

I think I can just point you to a link as it will better describe what I actually cannot...
See if this answers your your questions.
Regards,
Rudi

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BobH
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Re: Lossless, Lossy and Avatars

Post by BobH »

Thank you, Hans and Rudi!

Knowing about resizing algorithms might be handy.

The article pretty much confirms what I was trying to say, above.

Again, thank you both.
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HansV
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Re: Lossless, Lossy and Avatars

Post by HansV »

Some background here: Image scaling.
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BobH
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Re: Lossless, Lossy and Avatars

Post by BobH »

HansV wrote:Some background here: Image scaling.
That will keep me out of trouble for a good while, I reckon. :grin:
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Rudi
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Re: Lossless, Lossy and Avatars

Post by Rudi »

HansV wrote:Some background here: Image scaling.
That's almost TOO much info! :hairout:
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Rudi

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