What benefit .png over .jpg?

[Joseph Sinclair]

PNG addressed two problems with GIF.
1) GIF is an 8-bit format with an indexed color palette.  It's possible to do 24-bit color by overlaying a red, green, and blue image mask, but it's not ideal.  PNG is true 24-bit color with better compression.
2) GIF was, for a time, covered by patents on it's LZW compression, held by UNISYS that limited it's use in many situations.  Those patents are expired in 2003/2004 and there is no longer any patent encumbrance for GIF or LZW compression.

GIF has built-in support for animation, which PNG does not.  MNG provides animation of PNG images, and APNG provides a more recent alternative animation mechanism for PNG images that's easier to create but less efficient in compression.

I definitely agree that resolution matters most when printing.  A 1080p screen displays a 2 megapixel image, so more than that is not usually helpful for onscreen display (4 megapixel is fine for the rare 4K display).

I don't worry much about file size with 32G thumb drives and SD cards now common.  I figure 4,000 images (8 megapixel PNG) on a single thumb drive or SD card is more than enough storage for away-from-home use, and at home 2TB backup drives are pretty cheap these days.

BTW, typically 48 megapixel at 32-bit color (24 bits plus 8 bit alpha) is considered the minimum to match 35mm film.
The biggest remaining problem in digital is dynamic range (quality film is usually 3-5 stops, digital struggles to get 2).
The resolution difference isn't considered a big deal in most print publications (AZ highways is an exception, for good reason), so almost all professional photography is currently digital capture and workflow.


On 10/04/2012 05:29 PM, Derek Trotter wrote:
> 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.
>>
>>
>> ---------------------------------------------------
>> PLUG-discuss mailing list - PLUG-discuss at lists.plug.phoenix.az.us
>> To subscribe, unsubscribe, or to change your mail settings:
>> http://lists.PLUG.phoenix.az.us/mailman/listinfo/plug-discuss
>>
> 

-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 490 bytes
Desc: OpenPGP digital signature
URL: <http://lists.PLUG.phoenix.az.us/pipermail/plug-discuss/attachments/20121004/e09b9cdc/attachment.pgp>