Why is my raw image displayed differently in different viewers?

[nickdu]

This maybe a photoshop question so forgive me if it's not appropriate.

I've been using BBPro to process my images. I just recently downloaded the trial version of Photoshop because it appears I had some dust on the camera lense and I need to edit the result out of the picture. To my surprise Photoshop displays the Canon 30D raw images differently than BBPro. In my opinion the BBPro display is correct. The Photoshop image appears to have a blue tint to it. So my question is why would the same raw image display differently in two different applications?

I thought that maybe it's just displaying it that way for some reason and if I edited it and saved it to another file and displayed it in BBPro it would look ok. I was wrong. After editing out the dust artifact and saving the photo I loaded it in BBPro and the blue tint showed up in the BBPro image. I did notice that Adobe Camera Raw utility after opening the raw image displays the color as Adobe RGB (little link at the bottom of the camera raw utility). But the Canon 30D stores the image as sRGB, right? Could it be a problem with the Canon 30D plug-in?

I decided to check the RGB values of similar spots on the image in both BBPro and Adobe Camera Raw. The RGB values are different. So my question is: what's stored in the raw file? Aren't the RGB values stored there? If so, wouldn't you expect both viewers to have the same RGB values for the same pixels?

Thanks,
Nick

[Clive]

As a preamble to answers that may be more specific -

You never see a "raw" image. It could be represented, but would look more like a colour-blindness test chart! The raw image file is not intended to be seen by humans.

What we see is always an interpretation, including the jpeg display on the camera's lcd. This interpretation is sometimes determined by the various settings for contrast, saturation, skin toning, white balance, etc, in the camera, or Exif data stored with the image, or something completely of the software designers' choosing.

Even a jpeg interpretation of course depends on your colour management procedures for colour space, monitor luminance, colour profiles, etc.

The point is - we see only an interpretation, so we need to control the parameters and devices that give rise to the interpretation.

[nickdu]

Ok, but the camera stores some sort of RGB values, correct? If so, should a pixel of a certain RGB value look the same in all viewers on the same machine/monitor?

Nick

[DavidB]

A couple of points to add to Clive's explanation, which, I believe, is entirely correct.

If your photography goes back to the days of film, it is often convenient to think of a RAW file as a 'digital negative'. If you've had any experience of how different prints from the same negative can be, the differences in the way RAW files are interpreted by viewers will not be surprising.

For your 30D images, BB Pro will use the Canon libraries to convert the RAW files to JPEG or whatever. Also, for viewing RAW files, BB pro will use the JPEG embedded in the RAW image. This JPEG represents what will happen if the RAW file is converted 'as shot'. Of course, the whole point of RAW is that the user controls the processing. RAW processors which do not use the Canon libraries will have their own way of generating the preview image which will certainly not make use of any Canon proprietary settings.

The bottom line here is that there is no one absolutely right way of converting any given image. You have to use your own judgement as to what is right for you. Settings will also have to change depending on both the target audience and the means of transmission (print, web page, etc.). If that sounds complex and challenging, just experiment and decide what you like. If an image convinces you, the chances are that it will convince the target audience as well.

Hope this helps.

[nickdu]

It seems others have noticed the same/similar problem:

http://photo.net/bboard/q-and-a-fetch-msg?msg_id=00GmLH

It seems that ACR need a better profile that more closely matches the canon processing.

Nick

[Clive]

Actually, no, the raw file is not a standard RGB file, where one pixel has an R content, a G one and a B one.

It is a mosaic where 50% of the pixels are green, and 25% are red and 25%blue, in varying intensities. The file must go through a de-mosaicing process to make it an RGB image. There is more than one set of mathematical statements that can be used to do this. However, we would probably give up photography if we saw that output - many more stages are required to arrive at a possible interpretation of the original mosaic.

The surprise is not that there can be differences in the interpretation but that there can at times be such close agreement.

[Clive]

It seems others have noticed the same/similar problem:
http://photo.net/bboard/q-and-a-fetch-msg?msg_id=00GmLH
It seems that ACR need a better profile that more closely matches the canon processing. Nick
My 30D seems to require magenta correction, but Auto and Custom White Balance evaluates and documents the required colour correction on the Blue/Amber and Green/Magenta axes.

Unfortunately it seems that only Canon software makes proper use of those values. I use DxO to process CRW and CR2 files, and it acknowledges only one of those pairs. It refers to the other correction but ignores it. It's annoying that DxO say they are science-based, but ignore a hunk of it!

If you use Canon and have used the Breeze/Canon Libraries raw conversion, you will have seen the correction correctly handled. Few if any others do.

It's not just "profile" with ACR - its also the programming decisions and the algorithms used. There is not just one way to do the conversion, and the user-settable values do not always have the same meaning.

[nickdu]

That explains things a bit more. So if I like the BBPro (/canon) interpretation of the raw image and need to edit them in Photoshop what's the best way to do this? Should I use BBPro to export to a PSD file and use that in Photoshop?

Thanks,
Nick

[nickdu]

It's not just "profile" with ACR - its also the programming decisions and the algorithms used. There is not just one way to do the conversion, and the user-settable values do not always have the same meaning.

So is there anyway to get a Photoshop raw plug-in to use the canon libraries to interpret the images?

Nick

[DavidB]

So is there anyway to get a Photoshop raw plug-in to use the canon libraries to interpret the images?
Obviously, it's technically possible, but common sense suggests that Adobe will not readily make itself beholden to anyone else's proprietary libraries when they have the resources and commercial clout to write and promote their own. By the same token, the major camera manufacturers have studiously ignored Adobe's attempts to promote a standardised RAW format (DNG).

Of course, the end product matters more than the starting point, and posts in the thread to which you link point out that ACR can be calibrated to correct the problem. But, if it still worries you, you could use BB Pro or DPP to produce TIFF files which you could then edit in Photoshop. You could also use PSD as you suggest, but that will create issues with image metadata, which may or may not matter to you.