What benefit .png over .jpg?

[Derek Trotter]

Higher resolution allows for printing large pictures while maintaining 
picture quality. A few years ago I saw an article in Arizona Highways 
showing why they don't accept pictures in digital format. The had two 
photos of the same tree. One taken on film and one taken with a digital 
camera at several megapixels. Both looked equally as good. Then they 
blew up a small portion of the image. The film version looked great. The 
digital version was obviously of poor quality. The article went on to 
say what resolution was needed to equal the quality of 35mm film. I 
forget the number, but it was way higher than what was commonly 
available at the time.

Someone please correct me if I'm wrong, but wasn't png developed in part 
because of concerns about software patents relating to the gif format?

On 10/4/2012 17:16, joe at actionline.com wrote:
> Thanks.  Very helpful explanation.  I've always used .jpg almost
> exclusively and never noticed any degradation when editing.
>
> Guess I'll have to re-learn everything I thought I knew ;)
>
> Never did understand the need for 3, 5, 8, 10 or larger megapixel cameras.
>
> I take all my snapshots at about 1/2 megapixel jpg and then crop and
> further resize everything down to about 1/4th the original size, and I
> can't tell any difference in image quality, even with a jeweler's loop.
> I've sometimes printed an original and a resized smaller version at Costco
> and asked people to tell me which is better, and I've never found anyone
> who could tell any difference.
>
> People send these 3-megapixel (and bigger) images to me all the time and
> they are really slow to load. So, I've always used imagemagick 'convert'
> to bulk resize everything to about 1-20th the original size and they all
> look the same to me.
>
> On a recent vacation, I took more than 1,000 snapshots and by resizing
> them, they all fit on a single CD with lots of room to spare. I also
> upload our travel pix to a web page for our family to view online and by
> reducing the image size, all the images load and display very quickly and
> beautifully online.  With 3+meg image files it would take 20 times more
> bandwidth and 20 times longer to load and display.
>
> So, I just don't understand the benefit of keeping snapshots in gigantic
> image file sizes.
>
>
> -------
>> TL;DR,
>>    If you just want to have an image you can view and you want a smaller
>> file size, then use JPEG and don't edit it.
>>    If you want to edit the image or it's very small and speed of display is
>> important, use PNG.
>>
>> The two file formats are quite different:
>> PNG is *lossless* which means that you can edit, adjust, etc... the file
>> without losing any image data.  It stores all of the data in compressed
>> form, so it's larger, but everything from the original image is still
>> present.
>> JPEG is *lossy* it actually discards around 90% of the image data, so you
>> can't edit a JPEG without losing some of the image quality; by the third
>> or fourth edit a JPEG gets pretty bad.  It also uses some fairly complex
>> math to store and reconstruct the image, so it's much more computationally
>> intensive to view a JPEG compared to a PNG.
>> The system (generally) uses PNG for thumbnails because (for small images)
>> PNG is generally faster to create and faster to load due to less
>> computation needed to compress/decompress data versus reconstructing an
>> image from mathematical models.
>
>
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