"convert colors" causes jpeg compression?

Question

I recently had to re-install Acrobat, and since doing so whenever I run my preflight profile which is set to convert spot colors to cmyk, it's also apparently increasing the jpeg compression at the same time. Everything seems to be gaining bad jpeg artifacts after the color conversion (even when the colors being converted have nothing to do with the images).
It may be unrelated, but it also seems to be creating all sorts of ICC profile non-cmyk colors in the process. I.e., before "convert to cmyk for digital printing" I run a preflight that simply checks for non-cmyk colors. This profile warns me that there is a Pantone color in the ad. I check the separation preview and find only one or two things with Pantone colors. I then run the convert fix. The Pantone colors go away, but now there are sometimes dozens of items that are showing up as ICC profile colors, and this seems unfixable. I can't create a profile to convert them.
What's going on? Are there settings somewhere that can select the degree of (or lack of) jpeg compression? Why is it compressing the file at all? I have no such setting selected in the preflight profile. I tried creating a profile that does absolutely nothing at all but convert to cmyk, and it's still causing these problems.
This is using Acrobat 8. It's the same version, same disks, we used before, but these problems are new. I may have a setting wrong somewhere.

Answer 1

You are not making sense, and your methodology is fundamentally flawed.
Hitting Command+S without editing the file is NOT "saving".  It's not doing anything at all.  The program just idles.
You can verify this by observing that the file's modification date does not change.
Even your limited but flawed methodology will show the degradation if you change even a single pixel before hitting Command+S.  Then you will be degrading the image.  Just make a one-pixel change, for instance with the pencil tool, then save.  That is the same as doing a Save As.
Note that in your original query you were indeed changing a file by converting it to a different color space.  THAT is a change.
Independently from the above, your methodology of comparing two layers blended in Difference mode has the inherent limitation of the monitor's performance in displaying the shadows.  Your monitor, no matter how high-end, will NOT show you a difference between a 0,0,0 pixel (R,G,B,) and 0,0,1 or 1,0,0 or 1,0,1 for instance.  SAme goes for 1,0,2 etc., until you reach the lower threshold of your particular monitor.
There are two preferred methods of comparing two layers to see if they're identical.
Comparing allegedly identical images in Photoshop
The first one, championed by the late, lamented author and guru Bruce Fraser, is as follows [direct quote by copy and paste]:
A better way of comparing images with identical pixel dimensions is to use [Image menu >] Apply Image… > Subtract with an Offset of 128.
Difference only shows pixels that are lighter in the source than in the target (or maybe it's the other way around—I forget) where Subtract with Offset 128 shows differences in both directions.
Pixels that are identical in both images come in as RGB 128 gray, those that are different come in at a value that exactly reflects how different they are.
It also makes it much easier to spot subtle differences…
=== ===
The second one was suggested by someone in the Color Managament and Photoshop Windows forums, which follows:
(NOTE: only the methodology is of interest and pertinent, not the questionable context in which it has brought up and used.)
* 1) Open the two images to be compared in Photoshop
* 2) Move one image as a layer over the other one
* 3) select "Difference" as blending mode in the layers palette
* 4) now the whole image should appear seemingly black on the monitor
[So far this is the traditional, "time honored" method.]
* 5) select the magic wand tool with these settings: Tolerance: 0/ Anti-alias: no/ Contiguous: no/ Sample All Layers: yes
* 6) click somewhere into the formerly gray area
[This refers to an image of a Color-Checker type of card that had wide gray border around it. The test, therefore, requires a pure gray image in the image, something highly unlikely to change, in order for the magic wand to select all pure-black images (255,255,255). Such a border can easily be created around an image by increasing the canvas size and filling the newly created space with pure gray (128,128,128). ]
    Explanation: you just selected all completely black pixels (0,0,0) i.e. all pixels that are identical in both layers.
* 7) you should see "marching ants" forming rectangular patterns
* 8_) invert the selection (Shift Command I)
   Explanation: the selection now covers all the other pixels, i.e. all pixels which are different between both layers.
* 9) create a new empty layer and select it in the layers palette
* 10) set the foreground color to white
* 11) fill the selection with white (Alt+backspace on Windows, accordingly on Mac)
* 12) set the blending modes of all layers back to normal
    Explanation: you now see all identical pixels in their respective color and all different pixels in white.
This method is a lot more sensitive than the traditional one which stops at step #4 above.
Finally:
jfraze wrote:
Wow, the level of hostility is amazing on these adobe forums…
Only because people like you come in here itching for a fight, rather than to seek help.  It's just the way you choose to react—and to intereact with others.
Wo Tai Lao Le
我太老了