Image Batch Processor - Option to disable chroma subsampling (4:4:4 / 1x1)

[jarraun]

Hi all,

Unless I´m wrong, the Image Batch Processor when output JPEG files applies chroma subsampling to the files at maximum level: 4:2:0 / 2x2. Some people state that this way 75% of the Chroma resolution is destroyed, see here:
https://www.flickr.com/groups/capturenx/discuss/72157645476303083/
and here:
http://www.impulseadventure.com/photo/chroma-subsampling.html
I´d like the Image Batch Processor could have the option to disable chroma subsampling, quote from second link:

The resolution of chrominance information (Cb & Cr) is preserved at the same rate as the luminance (Y) information(4:4:4 / 1x1)

to preserve the maximum color quality in JPEG files.

Javier

[ubacher]

Jpeg is a lossy compression format. It seems you are complaining here about the kind of loss
which is used.  If jpeg at minimum compression is not to your liking you should use a loss-less format.

[jarraun]

Ubacher,

Thank you for your answer, sorry but I´m not complaining, just have launched a feature request.
I actually need compressed JPEG´s and having the possibility of saving them in IM5 with the best quality would speed up my workflow. the problem here is that JPEG´s seem to be rendered in the Image Batch Processor at maximum compression, not minimum and this seems to be noticeable in a little loss of quality in the reds an blues of the images. Files would be a little bigger buy I´d prefer loosing space in my drives and not colours in my images.

Javier

[Mario]

The Batch processor allows you to control the compression for JPEG. The default quality is 85, which is a good trade-off between file size and quality.
IMatch uses 2, 2, 1, 1, 1, 1 (Y h/v,Cb h/v,Cr h/v) for chrome subsampling. So far nobody ever has complained.

[jarraun]

Mario,

No doubt, I´m not an expert in color, may be different compression metods I´m not aware of, I may be wrong and the JPEG´s rendered by IM5 are as best as any others but theese seem to be the facts:

File: javimg20140627_190506_IM5

TIF file converted in Image Processor with "SettingsImageProcessor"

Report from "ExifToolGuy"

Report from "JeffreysExifViewer"



[attachment deleted by admin]

[ColinIM]

(....) So far nobody ever has complained.

Well ... ummm... No complaints so far until we have had a reason to look behind the (IMatch) scenery .... or until we've had this detail about IMatch's Batch Processor pointed out to us.  Thank you Jarraun!

+1 for this Feature Request.

I admit that I'm jumping ahead of myself here by supporting Jarraun's request because I haven't reached the point in my IM5 implementation where I've used the Batch Processor to export JPEG files.  Also, I'll admit too that in another context during the IM5 beta phase I almost replied to a different Forum discussion to urge strongly that development of the IMatch DAM feature set should emphatically not be distracted by any "image processing", or white balance correction options, or whatever non-DAM-related bells and whistles were being discussed at the time ...

However, given that this IMatch 5 Batch Processor is such a phenomenally powerful and flexible tool (it's hard to over-rate it!) and given the almost limitless parameter adjustments it offers for exporting, it would be a real shame if (as seems to be the case here) IMatch was not able to export JPEG files at really, actually, convincingly "100%" quality!

In my standard image processing (outside of IMatch) I jump through many hoops in order to retain all possible image data until the very last processing stage - which is usually the point where I'll export a 'final' JPEG-format file at "zero compression" or "maximum quality" based on my 'finally edited' RAW or 16-bit TIF image file.  I am hoping and planning for IMatch to be the main "output" cog in my photography workflow (after all image tweaking), but if I discover that I can't turn OFF chroma subsampling during an IMatch / final JPEG export then I'll be disinclined even to use IMatch for creating my 'final' JPEGs at all.

Yes, these minor sub-sampling details matter! They matter to me because I want to know where and when my image-quality is (sometimes unavoidably) eroded; the details matter too to the printing company to whom I'll complain if they can't optimally render the carefully colour-managed images in the JPEG files I send to them (putting sRGB / printer ICC profile limitations aside for now) ... and these details matter also to my Picture Library / Agency, to whom I promise to send the highest-possible quality JPEGs (in spite of the sad irony that even the highest possible quality 8-bit JPEG carries only a fraction of the image colour-data that was in the RAW file or in the 16-bit TIF image from which it was exported!).

So yes, I'd be a very happy chap if IMatch's JPEG-processing could be re-tuned or enhanced to remove any doubts or uncertainties about output colour sub-sampling.

Colin P.

[Mario]

I've made a few tests on Sunday to see which parameters are available.

I decided to slip this in under the hood. If a JPEG quality > 70% is requested, IMatch now disables chroma subsampling completely. This gives the best possible output quality and files which are maybe 5% larger. Under quality 70 the effect of chroma subsampling can be ignored anyway. The default compression ratio in the Batch Processor is 85%.

I've also implemented this change in the IMImage scripting class.

[sinus]

A very good solution! 

[Ferdinand]

It will be interesting to see how this works in practice. Bibble 5 did something similar and the resulting JPGs were much much larger.  I have a hunch that 70% is too low.

[Mario]

I think that most users will use 85% anyway.
The resulting change in file size is about 2% to 5%. If you want really small JPEG files, set quality to 50 to 60.

[ColinIM]

Thank you Mario!
Very much appreciated here.
Colin P.

[jarraun]

Mario,

Outstanding support, it´s going to be really helpful for me, I hope for others as well.

Thank you.

Javier