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, j...@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@lists.plug.phoenix.az.us >> To subscribe, unsubscribe, or to change your mail settings: >> http://lists.PLUG.phoenix.az.us/mailman/listinfo/plug-discuss >> >
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