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geekhack Community => Off Topic => Topic started by: BigBrother on Wed, 09 June 2010, 23:08:14

Title: image quarity thread ~
Post by: BigBrother on Wed, 09 June 2010, 23:08:14

Ok, you researcher freaks, crawl out of your dens and broken recliners and get me a proper answer: JPEG (1x1, 1x1, 1x1, 1x1) or PNG (adam7 + proper compression) ?

JPEG (1x1, 1x1, 1x1, 1x1):

Quote

Show Image

(http://img808.imageshack.us/img808/4383/1001834.jpg)

PNG: (etc, etc...)

Quote

Show Image

(http://img809.imageshack.us/img809/23/1001834.png)

(ok, maybe the PNG doesn't have  adam7 on it, i may have forgotten, but either way...)

for photographic images, i can see how a well-done JPEG will suffice but for stuff like user-created images or per-user generated images, PNG would be better, right ?

Title: image quarity thread ~
Post by: Mith on Thu, 10 June 2010, 09:06:03

I have no idea, but warm greetings to fellow scaper ;)

Title: image quarity thread ~
Post by: mr_a500 on Thu, 10 June 2010, 10:09:52

Quote from: ripster;191626

I'd worry more about your photography skills.  The composition of the cup is uninspiring.

I agree. He could have had a squirrel there... or at least a seal. :madgrin:

Title: image quarity thread ~
Post by: Rajagra on Thu, 10 June 2010, 10:24:33

At those compression ratios they are essentially identical images. I loaded them as layers and had it work out the difference. It produced what looked like a black image. No pixel was greater than a value of 4 (of a possible 255.)

I took your png file, saved it as a 219KB jpg file (your jpg is 1.19MB). I computed the difference between your 1.75MB png and my 219KB jpg. Again it seemed to be a black image, but checking showed some pixels were up to 33 in value (13% gray.)

So... your images are both fine for image capture and processing. For saving final results they are both massively over the top.

Edit> But general advice ... capture, create and edit using a lossless format where possible (RAW, BMP or whatever). Publish result using the format that suits the needs. JPG gives great compression. GIF allows transparency and animation. PNG allows smoother transparency (partial transparency where GIF only does on/off transparency.)

Title: image quarity thread ~
Post by: BigBrother on Thu, 10 June 2010, 10:34:45

Quote from: ripster;191626

I'd worry more about your photography skills.  The composition of the cup is uninspiring.

get me a macro-free DSLR and i'll be able to take more inspiring pics.

Title: image quarity thread ~
Post by: BigBrother on Fri, 11 June 2010, 16:35:46

Quote from: Mith;191617

I have no idea, but warm greetings to fellow scaper ;)

i just caught on... :/
are you from tip.it as well?

Title: image quarity thread ~
Post by: eyesnine on Tue, 28 June 2011, 00:02:49

PNG uses lossless compression. It looks good, but the file sizes are quite large compared to jpg. You're right that jpg is usually good enough for a photograph.

PNG is good when what you're compressing has a lot of pixels of the same few colors. For example, something created with a vector illustration application. Then, it works much better than jpg - the file sizes are very small and every pixel looks exactly as it did when it was originally rendered.

Anyways, anyone here know what kind of transparent image formats this site supports?

Title: image quarity thread ~
Post by: curzen on Tue, 28 June 2011, 00:43:37

doesn't matter, I'll still see the pixels and can tell it's photoshopped

Title: image quarity thread ~
Post by: eyesnine on Tue, 28 June 2011, 00:56:51

Quote from: eyesnine;369264

PNG uses lossless compression. It looks good, but the file sizes are quite large compared to jpg. You're right that jpg is usually good enough for a photograph.

PNG is good when what you're compressing has a lot of pixels of the same few colors. For example, something created with a vector illustration application. Then, it works much better than jpg - the file sizes are very small and every pixel looks exactly as it did when it was originally rendered.

Anyways, anyone here know what kind of transparent image formats this site supports?

PNG transparency tests OK.
(http://dl.dropbox.com/u/603429/G80-8113.test.png.png)

Title: image quarity thread ~
Post by: TacticalCoder on Sun, 03 July 2011, 10:31:25

Disclaimer: I've actually written image encoding/decoding algorithms.

Compression does not equal loss.  The two are totally different.  You can have lossless uncompressed (BMP), lossless compressed (PNG), lossy compressed (JPG), etc.

Quote from: Rajagra;191641

using a lossless format where possible (RAW, BMP or whatever).

First there's hardly any reason to recommend BMP over PNG.  BMP is unnecessarily wasting bandwith / storage.

Then it's a common misconception that RAW is lossless.  It typically is not even though there can be some lossless RAW.  Now if you're talking about "RAW" coming out of most digital camera and if the loss in these RAW is perceptible or not to the average user is another topic entirely.  But RAW typically is lossy and that is a fact (more on this later).

Also recommending RAW hardly makes sense unless the OP is into high-end digital photography and owns a camera able to ouptut RAW (whatever "RAW" means, more on this latter).

Note that I'm not saying that RAW is always lossy: I'm saying that RAW is typically not lossless.  (I point that out so that people don't come distorting my words).

Also, your sentence make it sound like PNG is lossy: PNG is typically not lossy.  PNG is compressed but lossless up to 48-bit RGB or 64-bit RGBA pictures (up to 16 bits per pixel per each R and G and B component and optional alpha value).

So if your source has 48-bits per pixel or less, then the resulting PNG shall be compressed but totally lossless: it won't add any loss.  As far as I know if your picture has more than 16 bits per pixel per value then it's the only case where PNG become lossy: this however would be very rare and the general consensus is that PNG is a lossless format.

For example if you take a picture with a digital camera and save it to "RAW" then convert it to PNG the PNG won't add more loss than the loss added by the camera when saving to RAW (if any loss there is, but in typical camera/settings RAW shall be lossy).  Not that you would want to do that: because PNG typically ain't a good choice to save pictures coming out of a camera.  I just took it as an example to show that PNG won't add loss.

The issue with RAW is really messy because "RAW" doesn't mean anything: it's not a standard, it's doesn't mean "lossless".  "RAW" really doesn't mean much besides "not crapily lossily .jpg encoded".  Besides that, there are several types or "RAW": uncompressed lossless, compressed lossy, etc.

Here's one example (amongst a huge lot of examples clearly detailing why RAW in most cases is not lossless) of a pro's take on the "RAW" subject (Google is your friend):

Nikon makes no claims that the format is lossless, but they say that the amount of information that is tossed out is insignificant, and that the format’s algorithm is “not visible lossy” or something to that effect. Obviously, if you’re chosing not to shoot JPEG, the idea of losing image data seems to negate one of the entire reasons to shoot raw.
...
It’s definitely lossy, whether or not that loss is perceptible to the average user. The raw sensor has a range of 0-4095, but a non-linear curve reduces this to the range 0-682.


PNG is lossless: you'll get exactly the same pixel values when decompressing what you compressed using PNG.

RAW is often lossy in that it is not saving the picture your camera really took (once again, there are many "RAW" types and many different RAW outputs depending on your camera and camera settings, "RAW" really doesn't mean much).

The Wikipedia article on RAW is quite exhaustive (and clearly states the fact that there are lossy RAW formats and points to the specs):

http://en.wikipedia.org/wiki/Raw_image_format (http://en.wikipedia.org/wiki/Raw_image_format)

I know that I used the words "often" and "typically" a lot but basically I'm just stating facts here.  A friend of mine who worked on the Photoshop codebase would probably explain all this better than I can (and english ain't my native language)   :)

Title: image quarity thread ~
Post by: HaveANiceDay on Sun, 03 July 2011, 10:52:32

Quote from: TacticalCoder;372441

insert good RAW info here

Thanks for writing that. Didn't know a lot about RAW.

Title: image quarity thread ~
Post by: sordna on Sun, 03 July 2011, 11:29:50

Wow, look how vbulletin scales the PNG preview image much worse than the JPG one though!
The scaled PNG is blurry!

Title: image quarity thread ~
Post by: woody on Sun, 03 July 2011, 12:17:29

Quote from: TacticalCoder;372441

Compression does not equal loss ... You can have lossless uncompressed (BMP), lossless compressed (PNG), lossy compressed (JPG), etc.

I have written this already on GH:
JPEG can be easily lossless and still with some compression ratio. On some GUIs this could be "100% quality" along with some other options.
In theory, JPEG has selectable level of "loss". In practice, most implementations suck and offer few predefined levels which aren't even derived from picture content.

Title: image quarity thread ~
Post by: keyboardlover on Sun, 03 July 2011, 12:29:23

To get around it post it like this instead:

(http://geekhack.org/attachment.php?attachmentid=20016&d=1288012932)

Luv,
The #1 HTML expert on the planet.

Title: image quarity thread ~
Post by: keyboardlover on Sun, 03 July 2011, 12:40:41

I personally like memes, videos and Ducky jokes.

BBL, its time for grilling. They don't call me the #1 Grill Master on the planet for nothing!

Title: image quarity thread ~
Post by: HaveANiceDay on Sun, 03 July 2011, 14:23:03

Quote from: woody;372526

I have written this already on GH:
JPEG can be easily lossless and still with some compression ratio. On some GUIs this could be "100% quality" along with some other options.
In theory, JPEG has selectable level of "loss". In practice, most implementations suck and offer few predefined levels which aren't even derived from picture content.

 
I don't think you know what is meant by lossless.
Lossless is not the same as visually indistinguishable from the original.

Try compressing a pic with 100% jpeg. Then take the output and compress it again with 100%.
Repeat multiple times. The end result will be different from the first uncompressed pic.

A PNG can be re-compressed billions of times, and it will remain the same. Hence, lossless compression.

Title: image quarity thread ~
Post by: 7bit on Sun, 03 July 2011, 15:19:06

Quote from: BigBrother;191534

PNG adam7 vs. JPEG 10918-5

 
Just use what gives smaller files. If an image has only a few colors, use PNG. Or just generate both and compare. you can also write a little script which does the comparison automatically!
If you also want to compare quality, just subtract both images from the original and sum up the absolute values. The one with the higher distance must go!

(http://geekhack.org/attachment.php?attachmentid=20019&stc=1&d=1309725700)
Ah, I should have looked at your GIF avatar before posting:
A pondering Panda, again!

Title: image quarity thread ~
Post by: RoboKrikit on Sun, 03 July 2011, 15:23:45

Quote from: BigBrother;191646

get me a macro-free DSLR and i'll be able to take more inspiring pics.

 
"Wow, what an amazing photo, you must have an awesome camera!"

ಠ_ಠ

Title: image quarity thread ~
Post by: 7bit on Sun, 03 July 2011, 15:32:16

Quote from: RoboKrikit;372614

"Wow, what an amazing photo, you must have an awesome camera!"

ಠ_ಠ

ಠ_ಠ

Title: image quarity thread ~
Post by: woody on Mon, 04 July 2011, 03:47:39

Quote from: HaveANiceDay;372599

I don't think you know what is meant by lossless.
Lossless is not the same as visually indistinguishable from the original.

Dude, don't take offense, but you don't seem to know what JPEG really is. I'd suggest reading and understanding the specs for full insight.

Quote from: HaveANiceDay;372599

Try compressing a pic with 100% jpeg. Then take the output and compress it again with 100%.
Repeat multiple times. The end result will be different from the first uncompressed pic.

Nope.

Title: image quarity thread ~
Post by: BigBrother on Mon, 04 July 2011, 04:56:41

ripster is worthless now. a used ****puppet.

anyways, good job on the grave dig, ladies and gentlemen.