JPEG and color management

Well, I went over much of the black rectangle at 3200% view and did see detect, by way of the Info Panel, some pixels with RGB values like 0,0,1 or 1,0.1 or 1,0,0.

Frankly, that's a hell of a lot better than I, as a JPEG hater, would have ever expected a damned JPEG to do, even at maximum quality. :D

Mark,

Mind you, I am a notorious JPEG hater and avoid them like the proverbial plague. I only use them to upload screen shots or other images to Pixentral to illustrate a point.

Mark, <br /> <br /> When using the Magic Wand <i>(which I confess I don't understand what that is supposed to prove)</i>, I used your settings, but I also went to the "Refine Edge" button and zeroed out all the values (Radius, Contrast, Smooth, Feather, Contract/Expand), and the selection preview was on <i>"Preview the selection over a black background"</i>. <br /> <br /> The result was a black rectangle with non-continuous marching-ants lines over the spots where the dividing lines between the colors as well as the numbers and letters would be. I expect that to be the JPEG artifacts. <br /> <br /> Because the selection is NOT continuous, this happens when I Fill with White: <br /> <br />c <a href="http://www.pixentral.com/show.php?picture=1mCX2jLqoBGgGrx3neLL8FvolXqo0Z0" /></a> <img alt="Picture hosted by Pixentral" src="http://www.pixentral.com/hosted/1mCX2jLqoBGgGrx3neLL8FvolXqo0Z0_thumb.jpg" border="0" /> <br />c (screenshot) <br /> <br /> Now what?

> Now I just went through the same exercise with your own JPEG (a3gencolorhighwwwfhoemdjv4.jpg) with identical results as those described above. No difference.

Ramon, use the original png and the image your conversion to .jpeg as posted by you on pixentral. Did you use the magic wand as described above ?

I compared the .jpeg file you uploaded to the original. I used an external command line program to compare the images, not in Photoshop in order to exclude the possibility of any wrong Photoshop settings on my behalf:

The result is:
Your .jpeg file is considerably different (so the black you were seeing, wasn't really black everywhere):
Compared to the original png file, 334103 of a total of 761000 pixels are different (=43.9%).

The different pixels are denoted in red in the following image:

http://www.imageboo.com/files/rjnce6kztdif5drtw75u.png

[large image replaced with link]

Now I just went through the same exercise with your own JPEG (a3gencolorhighwwwfhoemdjv4.jpg) with identical results as those described above. No difference.

How are you determining the difference you think you see?

Thanks for looking into it Ramón.

> When you opened the original PNG, did you ASSIGN the sRGB profile to it?

yes.

> Dragging the JPEG as a layer on top of the PNG, then setting the top layer to Difference blending mode, I get a solid black rectangle.

That's exactly what I did. Now use the magic wand with these settings:
tolerance: 0
anti-alias: no
contiguous: no
sample all layers: yes

Fill the selection with white and you get the results I posted here. If your image is completely black (or white after selecting and filling), your images are really identical.

This would show, that there is either a problem with PS CS3, or with my settings somewhere.

>Dragging the JPEG as a layer on top of the PNG, then setting the top layer to Difference blending mode, I get a solid black rectangle.


Not only that, leaving the blending mode to Normal and toggling the visibility of the top layer off and on, I see no percetible difference in any of the colors.

When you opened the original PNG, did you ASSIGN the sRGB profile to it?

Why are you saving it as a JPEG, a lossy format? For what possible purpose? <br /> <br /> Well, let's leave that aside, as it is really none of my business. :/ <br /> <br /> I downloaded the PNG straight from the browser to a folder (not my Desktop). I opened it with Photoshop 11, and saved one copy as a PSD, a TIFF, and a Quality-12 JPEG. I see nothing like what your image shows. Here's my JPEG on Pixentral: <br /> <br />c <a href="http://www.pixentral.com/show.php?picture=1vCQGy0rp4Cj826NOvgAtzKM40Z1" /></a> <img alt="Picture hosted by Pixentral" src="http://www.pixentral.com/hosted/1vCQGy0rp4Cj826NOvgAtzKM40Z1_thumb.jpg" border="0" /> <br />c Click on the thumbnail for the full image. <br /> <br /> Dragging the JPEG as a layer on top of the PNG, then setting the top layer to Difference blending mode, I get a solid black rectangle.