July 22, 2018, 01:15:47 AM

Author Topic: Preserving colors (color space?) when uploading jpg files to this forum  (Read 8477 times)

iKenndac

  • EOS Rebel 300D
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PNG has it's applications, and better resolution and color information (with higher file size as the tradeoff)... is one of them.

24-bit PNG has 8 bits per channel, same as JPEG. There is no more colour information in a PNG than a JPEG.

PNG is lossless compression, where JPEG is lossy. In terms to quality:filesize, PNG's compression algorithms do better at simple graphics with sharp edges and uniform colours, where JPEG is better at your typical photograph.

Even the PNG website (under "Typical Usage") says that JPEG is better for this kinda stuff:

Quote
Note that for transmission of finished truecolor images--especially photographic ones--JPEG is almost always a better choice. Although JPEG's lossy compression can introduce visible artifacts, these can be minimized, and the savings in file size even at high quality levels is much better than is generally possible with a lossless format like PNG.

If you're going to print your photo, then lossless is what you want. For a tiny version that's going to be displayed on a web forum using browsers already established to be terrible at colour management on crappy 6-bit displays, a big PNG file is probably overkill. If you're going to do that, you may as well just post up DNGs and be done with it.

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LetTheRightLensIn

  • Canon EF 400mm f/2.8L IS II
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Hello, Everyone.

I changed monitors recently (low-end, consumer-grade, not graphics- or photography-specific), and Windows 7 Professional (64-bit) recognizes the replacement monitor and has assigned the associated ICC/ICM profile for it.

When I view images on my machine, they look fine.  When uploading them to the forum here, it's as if they've become desaturated or washed out.

I can simulate the desaturated look by viewing the jpg files with no color profile associated.  Once I make the association, the viewer I use recognizes it, and the image looks normal.  Photoshop renders the image properly all the time.  Even "Windows Preview" renders the image properly.

Does anyone know what I should do in order to upload an image here that will look "normal" and not desaturated?  I thought I had jpg files saved with embedded color profiles, but maybe I missed something.  With my other monitor, this issue did not exist.

it sounds like you are uploading adobergb or prophotorgb files and then using a non-color managed web-browser. Use firefox with color-management set properly and it'll look fine (although if the images don't need the extra wide gamut colors then it's better to convert to sRGB first so people running whatever browser won't have issues, if has really rich colors of certain types wide gamut is good though).

LetTheRightLensIn

  • Canon EF 400mm f/2.8L IS II
  • *********
  • Posts: 4757
PNG , Portable Network Graphics, is designed for graphics, that is illustrations that often have hard edges and gradients, they are very inefficient for jpegs of images. Not my opinion, recognised fact.

As for the artifacts you think you see, I suspect they are imaginary, don't forget this is a re-sampled screen shot of sub 100% views, there are so many stages of re-sampling here it is beyond imagination.

Overhead, sure a few hundred k is not much, however the logical extension is when you multiply everything by 3-10 times, you end up running 3-10 slower.

it still takes less space than TIFF though and you get lossless compression 16bit per channel

I wouldn't use PNG for web though, but for personal usage on your own computer.

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