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Thread: quality loss in IrfanView's lossless conversions?

  1. #21
    Professional User Skippybox's Avatar
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    Not at all, I just wasn't around to notice.

    Check it out for yourself.

    PictureGear I think is OK.
    Attached Images Attached Images

  2. #22
    Multiple User boarder's paradise's Avatar
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    thanks for the additional images. You have quite some apps

    He,he, ... yes you are right PhotoStudio is way off and PictureGear generates exactly the same image as IrfanView and all the other apps. Now I am curious ... how did you know ??

    Anyway, I'm happy ... the list of applications I can throw at them @Adobeforums grows and grows ....
    That's what I call teamwork in times of web2.0
    Last edited by boarder's paradise; 06.12.2008 at 02:41 AM.

  3. #23
    Professional User Skippybox's Avatar
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    Only a handful of what I have...

    I looked at the same three pixels as before and figured so.

    It's possible that most applictions use the same popular codec, but maybe the others are using a variation that is also possibly better quality. If you can't tell out of 16.7 million colors which one is better, then why worry?

    I feel for your curiosity, as I have curiosities, too. However. considering the time you are willing to devote to this, over that of whatever this is intended for, you could probably learn the standard and figure out why this is happening. But, most people don't wish to; they just accept or trust the technology. Most people would rather spend their time being one of the people in the image.

    Like others have said, jpg is lossy at any compression level, so why should decompression be perfect? If one is willing to use jpg at all, quality surely cannot be a factor in their work, as jpg is not synonamous with quality at all. You don't seem to question why jpg is used so prevalently, which I think is a far worse problem.

  4. #24
    Multiple User boarder's paradise's Avatar
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    Quote Originally Posted by Skippybox View Post
    Only a handful of what I have...
    wow

    Most people would rather spend their time being one of the people in the image.
    yes, you are so right ...

    Like others have said, jpg is lossy at any compression level, so why should decompression be perfect?
    I thought jpeg-encoding is lossy, jpeg-decoding is lossless. People over there at adobeforums.com have different opinions about it.

    If one is willing to use jpg at all, quality surely cannot be a factor in their work, as jpg is not synonamous with quality at all.
    I don't use it for work anyway. But there are some repercussions/interference with understanding color management, and that's an issue that's important for me, so I wanted to figure out the jpeg-stuff as well.

    You don't seem to question why jpg is used so prevalently, which I think is a far worse problem.
    You are right. What do you use? RAW and lossless jp2 ?

  5. #25
    Multiple User boarder's paradise's Avatar
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    Quote Originally Posted by Skippybox View Post
    The exact version [of Photoshop Elements] is 1.0.128.0.
    Skippybox, are you sure? Because the current version is 7.0. If you have 1.0 it must be some 10 years old or so ... is that possible ?

  6. #26
    Professional User Skippybox's Avatar
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    Yes, it is the original PhotoShop Elements. It came preinstalled on my notebook, which is 7 years old. I saw no reason to upgrade, since I don't use it too much and there are free software titles that do about the same things. Maybe I'll upgrade someday, huh?!

    I keep many thing a while, as there really isn't a reason to pay for a few features in an upgrade. Besides, it runs fine being small. I couldn't run 7 if I wanted to anyway!
    Last edited by Skippybox; 09.12.2008 at 10:26 PM.

  7. #27
    Multiple User boarder's paradise's Avatar
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    I see. No, you are right. Never change a winning team

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    The differences are related to dct method and fancy upsampling.

    The Discrete Cosine Transform (DCT) method works with blocks of 8x8 pixels and all those calculations by approximation affects visual representation.

    Here is part of a header file

    Code:
    typedef enum {
    JDCT_ISLOW,     /* slow but accurate integer algorithm */
    JDCT_IFAST,     /* faster, less accurate integer method */
    JDCT_FLOAT      /* floating-point: accurate, fast on fast HW */
    } J_DCT_METHOD;
    As you can see there are different methods and programs may use one of them.

    The JPEG default colorspace is YCbCr.
    The components are downsampled during compression by the chroma factors and later upsampled during decompression.
    This upsampling is handled differently by different programs.

    Fancy upsampling is a option of IJG library to better approximate the original component values. I don't know what Photoshop is using but I heard it simply uses a fast method.
    The original IJG library uses also some kind of resampling methods for approximation like nearest neighbor (box, pixel replication),
    or bilinear interpolation (triangle). They can introduce pixelation or blurring.

    The IJG code is very technical and it takes someone with strong mathematical and programming knowledge to understand it. Also you need to understand first the JPEG papers. i don't know exactly what JPEG does internally to explain more than I did.

  9. #29
    Multiple User boarder's paradise's Avatar
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    Thanks so much for your insights, Lucian.

    I had asked the question at the official Adobe forum, too. Noone was able to give a technical comment like you do. You would be deerly welcomed over there, if you want:

    http://www.adobeforums.com/webx?128@@.59b726f1

    Quite a few of them are really talking nonsense and I feel you would be easily competent enough to expose that.

    But anyway, thanks a lot, your informations made me understand the whole thing a lot better.

  10. #30
    Professional User Skippybox's Avatar
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    Quote Originally Posted by boarder's paradise View Post
    I thought jpeg-encoding is lossy, jpeg-decoding is lossless. People over there at adobeforums.com have different opinions about it.
    I would think the same thing. Apparently, it isn't as lossless as we thought. I originally meant that if encoding is lossy, maybe decoding doesn't have to be so accurate anyway. Still, I would think that would lead to problems with constant saving because of the compounding degradedness just opening it!

    What do you use? RAW and lossless jp2 ?
    Well, if I can, I try not to use JPG, but obviously with a JPG world, I am forced to use it like anyone else is. I mean it is kind of stupid saying use it for the final output when most likely someone is going to grab it from the web or camera and end up editing it again.

    I try to use PNG, BMP, and TIF for some things. I wouldn't pay for a JP2 license. Most cameras have stopped supporting BMP and so JPG reigns. RAW isn't really a format, takes too much resources/time to fiddle with, and many times is lossy compressed anyhow. So for cameras, JPG is what I use. The best you can do is have a high quality camera, but mine can't shoot RAW.

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