If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below. |
|
|
Thread Tools | Display Modes |
#16
|
|||
|
|||
Image formats (was: Does the .png image format have a text metadata field?)
In message , R.Wieser
writes: Nospam, GIF, JPG, PNG all use different methods to compress the data only jpg and png compress image data. No, Mayayana is right. GIF compresses the image using LZW. https://en.wikipedia.org/wiki/GIF Regards, Rudy Wieser I think the confusion might be over what is meant by "compress[ion]" - which may be lossy or not. JPG uses lossy compression - the _degree_ of which is adjustable (depending on what's being used to create it, either a crude "quality" switch [many cameras just offer two or three], or a slider [sometimes labelled "per cent"], or a desired file size). It's still by far the most widely used format (probably because most cameras produce it, in all but expensive ones not giving any other option). Though lossy, and lots of people say you should _never_ re-save such an image, its compression is surprisingly good in many situations - not just many (arguably the majority of) photographs, but even scanned documents, where you'd think the compression would have worse consequences than it actually does. GIF uses lossless compression - provided there were only 256 or fewer colours in the original image. (It's thus great for many logos, and some cartoons.) If there were more, the encoder selects the best 256 (i. e. it's not the same 256 for all GIFs). For a surprising number of images, this _doesn't_ matter much - especially ones with lots of fine detail; it tends to show up worst in things with _gradual_ shading variation, such as the skies in sunsets, or a billiard ball, apple, or cheek. On the whole, though, I'd use .jpg (by default, at what IrfanView calls 80% quality, I think) _for photos_, if choosing just between those two. PNG was I thought invented because some of the patents on some of the others were keeping some lawyers in business; those have expired now though. It also, being a more-recently-devised format, has some advantages. Whether it uses - or _can_ use - lossless compression, I don't know; some in this thread have said it is lossless, but haven't said whether that's optional. I don't originate it myself so don't know much about it, but sometimes I download images that are in it, and I don't like converting unnecessarily, so I have some PNGs. -- J. P. Gilliver. UMRA: 1960/1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf " ... but ... on the sub-ether radio, [it said] you're dead!" "Yeah, that's right, I just haven't stopped moving yet." (link episode) |
Ads |
#17
|
|||
|
|||
Does the .png image format have a text metadata field?
In message , R.Wieser
writes: John, Not really; I only wanted a free-form text area (a "Comment" field if you like). Than you are home-free as they say. :-) Exif Pilot does seem to give me that - _and_ fixed fields for assorted dates, and other things, which _implies_ that those are in fact set down in the format. Are you saying they're not? No, I tried to say that you can use every field EXIF offers, but if you would want to add a, for example, "Comments_two" field you would be out-of-luck. No, I was just wondering if there was "Comments 1" - I thought maybe there wasn't, since IrfanView didn't offer access to it. Seems it (PNG) _does_ have such a field, just IV doesn't know about it. (I've emailed Irfan asking if a future version might.) The "character size" of an EXIF field is bound to its (numeric) type. You could introduce a new type, but if some other program isn't aware of that new type (and thus can't look-up the "character size") it will break its parsing of the EXEF datablob (as you do not know where the next field starts). No, I didn't want to invent a new one (as you say, that'd be no good to anything that knows about the standard ones) - just use the existing one if there was one. Which it appears there is. [] The newer image formats often have such an optional free-to-use block, the older ones not. Though IIRC the "newer" DDS image format doesn't have one either. No, I didn't want a "spare" block, only one for text. (Though I suppose in a format that didn't specifically have a text one, I could use that. But not necessary in this case.) [] -- J. P. Gilliver. UMRA: 1960/1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf " ... but ... on the sub-ether radio, [it said] you're dead!" "Yeah, that's right, I just haven't stopped moving yet." (link episode) |
#18
|
|||
|
|||
Does the .png image format have a text metadata field?
In message , Mayayana
writes: [] format, but that doesn't make it standard. I just tried a PNG with metadata in IrfanView. It didn't see the data. But actually, this PNG doesn't have data as such. It only has the labels, like Author, Description, etc. A second file has no labels. Seems the format _can_ have these fields; I don't know if that means _every_ .png _does_ have them. (In the same way a JPG _can_ have both EXIF and Comments, but doesn't _have_ to; in IrfanView, whether it does is shown by the presence or absence of asterisks on the EXIF and comment buttons.) It seems IrfanView doesn't yet know about the _possibility_ of these fields in the .png format, though. I'm surprised you care about this. I have a hard time even finding a PNG on my drives. The only ones I have are charts that I downloaded from webpages. Few suites use them because they're big. A JPG can show a photo image much smaller. A GIF can show a chart much smaller. I really don't understand why anyone uses PNG online. One could use PNG for compressed images on disk, but for that there's TIF. I don't originate in it, but as you say, sometimes downloads come in it - and I don't like to do needless format conversions. I have PSP 5 and 16. The former doesn't recognize JPG EXIF data. The latter saves it. I prefer the former. But ever since I had 5 and 7 - I think way back on my '98SElite machine. I preferred 5 - the only reason I ever used 7 was the odd image that was too big for 5 people started taking photos of everything with their phones, there's a big call for JPG metadata standardization. That won't happen with PNG unless there's a call for that. Which would probably require that PNG become the standard for low quality cellphone/camera photos. PNG is better in being lossless. But PNG also takes up more space, so that might not happen. When photos are just for sending between phones, quality doesn't matter much. 2 -- J. P. Gilliver. UMRA: 1960/1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf You can believe it if it helps you to sleep. - Quoted by Tom Lehrer (on religion, in passing), April 2013. |
#19
|
|||
|
|||
Does the .png image format have a text metadata field?
nospam,
it's actually both, since uncompressed gif avoids patent issues, although the patents have expired. https://en.wikipedia.org/wiki/GIF#Uncompressed_GIF I guess you got lucky googeling. Next time do not try to assert stuff you do not know much, if anything, about though. The above is the exception to the rule, but not even activily used - users ignored the patent issues (duh), and businesses simply used other image formats (to avoid to even be /accused/ of patent violations) and ultimatily came up with the PNG format to replace it. Regards, Rudy Wieser |
#20
|
|||
|
|||
Image formats (was: Does the .png image format have a text metadata field?)
John,
I think the confusion might be over what is meant by "compress[ion]" - I don't think so. GIF uses lossless compression So does PNG. But he named only GIF as /not/ using compression. Regards, Rudy Wieser |
#21
|
|||
|
|||
Does the .png image format have a text metadata field?
In article , R.Wieser
wrote: it's actually both, since uncompressed gif avoids patent issues, although the patents have expired. https://en.wikipedia.org/wiki/GIF#Uncompressed_GIF I guess you got lucky googeling. that's from *your* link. Next time do not try to assert stuff you do not know much, if anything, about though. The above is the exception to the rule, but not even activily used - it was used quite a bit. users ignored the patent issues (duh), and businesses simply used other image formats (to avoid to even be /accused/ of patent violations) and ultimatily came up with the PNG format to replace it. one of several reasons for png. |
#22
|
|||
|
|||
Does the .png image format have a text metadata field?
John
In the same way a JPG _can_ have both EXIF and Comments, but doesn't _have_ to; Are you sure about that ? The last time I edited the EXIF information in a JPG image using the "properties" dialog Windows has the "Comments" that I had also put in there where hoovered into the EXIF block. Definitily not what I expected or wanted. Or, in other words: You can put them in there, but its easy to lose the non-EXIF comment(s). Regards, Rudy Wieser |
#23
|
|||
|
|||
Does the .png image format have a text metadata field?
In message , R.Wieser
writes: John In the same way a JPG _can_ have both EXIF and Comments, but doesn't _have_ to; Are you sure about that ? If I open most .jpg files in IrfanView, and type i (for information), I get a popup table of information - mostly what has to be there, like filename, path, compression, size in pixels, and so on. At the bottom, there are a couple of buttons "IPTC info" and "Comment", as well as "OK" which closes it. (Some JPEGs also have an "EXIF info" button.) If I have added a comment, the comment button becomes "Comment *" (note the asterisk); similarly for the IPTC info one. I'm not sure how I can get the EXIF one to appear if it doesn't; I hadn't until now noticed that it is sometimes there and sometimes not for JPEGs (the Comment and IPTC buttons are always there, just not always with their asterisk). [I only ever use the Comment one; I don't usually touch EXIF or IPTC.] The last time I edited the EXIF information in a JPG image using the "properties" dialog Windows has the "Comments" that I had also put in there where hoovered into the EXIF block. Definitily not what I expected or wanted. On here (W7HP32, Classic Shell if that's relevant), the Properties box doesn't _have_ Comments tab. If you wanted to add something to a file but not have it become part of the file, where _did_ you want it to go - into the directory information somewhere? Each to his own, but I'd be concerned that it might not remain associated with the file if that was the case - if I moved, or even renamed, the file. Or, in other words: You can put them in there, but its easy to lose the non-EXIF comment(s). Whether EXIF or some other part of the format specification, there can always be the danger of loss, if the file is adjusted by software that either does not know about those fields, or which sets them to default values. Regards, Rudy Wieser 2 -- J. P. Gilliver. UMRA: 1960/1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf resentment is like drinking poison and expecting the other person to die - attributed to Carrie Fisher by Gareth McLean, in Radio Times 28 January-3 February 2012 |
#24
|
|||
|
|||
Does the .png image format have a text metadata field?
John,
On here (W7HP32, Classic Shell if that's relevant), the Properties box doesn't _have_ Comments tab. I was not talking about a tab (in the properties dialog), but about a freeform textfield thats part of (stored in) the image. You know, one of those iTXt, tEXt, and zTXt "chunks" that are defined for a .PNG image. Just to be /absolutily sure/ I just retried it with a .JPG image which had textual data stored in a 0xFFFE ID'd blocks (date, origional name). But after having entered some data in the image properties - summary dialog (mind you, XP here) the 0xFFFE blocks where gone, hoovered up by EXIF, and stored in it as 0x9286 (UserComment) records. But feel free not to believe me. Try it for yourself. Regards, Rudy Wieser |
#25
|
|||
|
|||
Does the .png image format have a text metadata field?
In message , R.Wieser
writes: John, On here (W7HP32, Classic Shell if that's relevant), the Properties box doesn't _have_ Comments tab. I was not talking about a tab (in the properties dialog), but about a freeform textfield thats part of (stored in) the image. You know, one of those iTXt, tEXt, and zTXt "chunks" that are defined for a .PNG image. Just to be /absolutily sure/ I just retried it with a .JPG image which had textual data stored in a 0xFFFE ID'd blocks (date, origional name). But after having entered some data in the image properties - summary dialog Can you explain in baby steps how you get to the "image properties - summary dialog", so I can do exactly what you're doing? (Are you starting from Windows Explorer, for example, or somewhere else?) (mind you, XP here) the 0xFFFE blocks where gone, hoovered up by EXIF, and stored in it as 0x9286 (UserComment) records. 7HP32 here. But feel free not to believe me. Try it for yourself. I'm not disbelieving you, just not sure where you're starting from. Regards, Rudy Wieser 2 -- J. P. Gilliver. UMRA: 1960/1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf "If even one person" arguments allow the perfect to become the enemy of the good, and thus they tend to cause more harm than good. - Jimmy Akins quoted by Scott Adams, 2015-5-5 |
#26
|
|||
|
|||
[OT]Does the .png image format have a text metadata field?
On Thu, 13 Feb 2020 09:14:39 -0500, "Mayayana"
wrote: "J. P. Gilliver (John)" wrote | Not really; I only wanted a free-form text area (a "Comment" field if | you like). Exif Pilot does seem to give me that - _and_ fixed fields for | assorted dates, and other things, which _implies_ that those are in fact | set down in the format. Are you saying they're not? | | Is there a general format for an EXIF "block", which the various image | file formats - .jpg, .png, etc.- just form a "wrapper" for? I had | assumed not, i. e. that each image file format had its own (some | optional) blocks, at least for things like photograph details (camera | model, date taken, lens and "film" settings, shutter speed, and so on). Each format is entirely different. Embedded metadata is mainly the invention of Adobe. Then it was useful and became standardized through use. But it's still not entirely standard. And EXIF data is not required for the format. Meanwhile, everyone and his brother have made up their own tags. Microsoft even created tags with unicode strings, breaking the rule everyone else follows. But it's their tag and it's an open standard. So whether this stuff is official depends mostly on how many people use it. JPG metadata is popular mainly because people want to tag their photos from Sally's wedding, and because journalists want to infest their photos with official copyright data, not realizing that data is not actually part of the image data but only an optional addition to the file header that can be easily removed. In general, file formats include a header and data. The header IDs the file type and can include a lot more info in some cases. But the only required parts are the parts that allow the file data to be interpreted as intended. These image files are raster images, which means they're all bitmaps. All of them store data that can be unpacked to provide a gridwork of pixel values in order to render the image. A BMP is little more that that data in a long string. You could actually count down into the file, if you wanted to, to find the RGB pixel values of the pixel at 300,400 offset from the top right corner. A TIF is usually just a BMP that's been zipped. GIF, JPG, PNG all use different methods to compress the data and all have unique pros and cons. But they're all ways to package a bitmap. If you look at the link you'll see a PNG is somewhat unusual. The header, such as it is, is only a few bytes IDing the file type. What's usually called the "file magic". The rest is blocks of data with identifying bytes. PNGs also come in a large number of types. It's a very complex format. And since there's no simple rule for putting metadata in a header, as there is for JPG, it's a more difficult task. Since almost all image formats are compressed, do you know a tool that can un-compress the data to look for "hidden" text or files? There's a lot of apps that do steganography, so there must be something to identify the method used (a generic un-packer). The NSA would be naked without one. LOL. Examples of steganographic tools: https://www.ostechnix.com/hide-files...-images-linux/ PS The "cat" method is too primitive. Or "copy /y /b image_file to_hide_file outputfile". You can see the text (or the file headers eg the PK of a zip) with a hexeditor. The best ones are those that imbed the text in the unused part of the image and then compress it. The file size doesn't change much, if at all. And the image does not lose its properties. I've strayed a bit from the topic. OT up... []'s -- Don't be evil - Google 2004 We have a new policy - Google 2012 |
#27
|
|||
|
|||
Image formats (was: Does the .png image format have a text metadata field?)
"J. P. Gilliver (John)" wrote
| PNG was I thought invented because some of the patents on some of the | others were keeping some lawyers in business; those have expired now | though. It also, being a more-recently-devised format, has some | advantages. Whether it uses - or _can_ use - lossless compression, I | don't know; some in this thread have said it is lossless, but haven't | said whether that's optional. I don't originate it myself so don't know | much about it, but sometimes I download images that are in it, and I | don't like converting unnecessarily, so I have some PNGs. As Rudy said, PNG is lossless, but it also has an alpha channel for transparency. So it doesn't dump data the way JPG does, and it also uses 4 bytes per pixel instead of the 3 that JPG does. That makes it bigger. Each pixel can have a percentage transparency, recorded in the 4th byte. I don't know of anything to recommend PNG, but it could make sense online where high image quality in 24-bit is needed. There's no other widely supported formate for that. The transparency feature is also nice, but I'm not aware of any program for creating finely detailed transparency. For instance, if you want a logo for "John's English Diner" and you want a knife and fork semi-transparent, how do you do that in one image? I don't know. |
#28
|
|||
|
|||
[OT]Does the .png image format have a text metadata field?
"Shadow" wrote
| Since almost all image formats are compressed, do you know a | tool that can un-compress the data to look for "hidden" text or files? | There's a lot of apps that do steganography, so there must be | something to identify the method used (a generic un-packer). | The NSA would be naked without one. LOL. | Mysterious. So it hides extra bytes? Since each format is different I don't know of any easy way to track it, or to create the hidden text. |
#29
|
|||
|
|||
Does the .png image format have a text metadata field?
"Java Jive" wrote
| TIFF files are *MUCH* bigger than PNG, for example 22.1Mb as opposed to | 8.24MB for the same picture. It sounds like you have a lot more experience than I do, but I don't see that. A TIF is basically a zipped BMP. I just tried converting a 252 KB PNG to TIF and got 217 KB. Then I tried saving a 5 MB JPG image with IrfanView (52 MB BMP). 4 MB for the TIF. 21 MB for the PNG. That's with compression level 6 and no transparency color. Though I assume PNG has to save the alpha channel anyway. So no advantage there. |
#30
|
|||
|
|||
Does the .png image format have a text metadata field?
On 14/02/2020 00:12, Mayayana wrote:
"Java Jive" wrote TIFF files are *MUCH* bigger than PNG, for example 22.1Mb as opposed to 8.24MB for the same picture. It sounds like you have a lot more experience than I do, but I don't see that. A TIF is basically a zipped BMP. I just tried converting a 252 KB PNG to TIF and got 217 KB. Then I tried saving a 5 MB JPG image with IrfanView (52 MB BMP). 4 MB for the TIF. 21 MB for the PNG. That's with compression level 6 and no transparency color. Though I assume PNG has to save the alpha channel anyway. So no advantage there. I only know for sure what I posted earlier, but it may be relevant that most of the TIFFs I've encountered have been conversions from the native image formats of Canon S40 and Nikon D5600 cameras. The example earlier was a TIFF from a CRAW image format of the Canon, converted to TIFF and by Canon's own software that came with the camera from an images saved by the camera as RAW rather than JPEG, and thence to PNG for use on my web site. For a Nikon example: 24.6MB NEF (I *think* their version of TIFF, but it could be their version of RAW) comes out as 10.MB PNG. |
Thread Tools | |
Display Modes | |
|
|