'Save as' and 'Subsample chroma'

[MikeA]

(Photo Mechanic 4.6.3 running under XP SP2)

When "Subsample Chroma" is selected, what is the most likely effect you'd see in terms of degradation of the image?

I've been trying "Save as" tests with and without this setting selected. In the output files, I can't detect any differences except for possibly a very, very slight increase in apparent sharpness in the files saved with "Subsample Chroma" selected. (I'm not using the Sharpen option, so I'm wondering if this difference might be caused by some very slight increase in contrast. Admittedly, it does take an almost-neurotic degree of pixel-peeping to see the difference.)

Images saved for web display at reduced sizes do sometimes need a bit of additional sharpening -- but not as much as they get in PM at the moment. In my experience so far, the 'sharpen' feature produces visible sharpening artifacts.

The 'save as' feature is excellent -- exactly what I've been looking for in a save-for-web routine. I hope that some day the amount of sharpening could be a user option.

[Kirk Baker]

Mike,

(Photo Mechanic 4.6.3 running under XP SP2)

When "Subsample Chroma" is selected, what is the most likely effect you'd see in terms of degradation of the image?

Turning this option on allows the JPEG compressor to subsamble color information in the image.  Rapid changes from one color to a completely different color (not just a shade change) will be affected most visibly.  But you really have to decrease the Quality setting to see these effects.  The positive side of using this option is that the image ends up being a fair amount smaller in size when encoded.[/quote]

-Kirk

[MikeA]

Turning this option on allows the JPEG compressor to subsamble color information in the image.  Rapid changes from one color to a completely different color (not just a shade change) will be affected most visibly.  But you really have to decrease the Quality setting to see these effects.  The positive side of using this option is that the image ends up being a fair amount smaller in size when encoded.

Kirk -- thanks for the information. I find that leaving the quality slider dead-center gives me roughly the file size I'm after (300K or less for 1204x768-pixel images made for the web). I'd have thought that kind of setting would produce small but noticeable JPEG artifacts (similar to quality '5' on a scale of 1 to 10 in Photoshop or other applications with a 'quality 1-to-10' selection) -- but it doesn't seem to. So perhaps leaving the 'subsample' option on for those kinds of saves would be ok. You're right that it makes a noticeable difference in the file's size.