Since Lightroom is so good, what do you use Photoshop for?

Started Apr 25, 2014 | Discussions thread
MiraShootsNikon Senior Member • Posts: 1,007
Bayer Interpolation?

Ron AKA wrote:

Dave Stott wrote:

This is a strange dialogue. Lightroom doesn't alter pixels 'cos a RAW file doesn't have any pixels. ACR likewise doesn't create a pixel based file till you exit it.

A RAW file has to have pixel data. That is basically what it has captured from the pixels in your sensor. Just look at the metadata for a RAW file, and it will tell you the height and width in pixels, and total pixels. What it doesn't have is a physical dimension such as inches. So there is no resolution in pixels per inch, just dimensions in pixels.

No. This explanation misunderstands RAW pretty significantly.

If you shoot a Bayer-sensor camera (everything but Sigma-Foveon), then your camera sensor's pixels are an alternating mosaic of red, green, and blue that get interpolated later to actually start looking like an image. The actual pixel data from a Bayer sensor looks nothing like a photograph, unless you're judging from the perspective of your third wild LSD ride of the day.

RAW processing is the business of assembling groups of red-green-blue pixel data from your camera's sensor into single pixels of a given color.

It's why the number of pixels your camera sensor has is not the same as the number of pixels in your processed raster image.

It's one reason (though not the only reason) why different RAW converters produce different-looking results with the same RAW data. They assemble or interpolate raster pixels differently.

It's why many RAW converters have a terrible time with Fuji X-Trans RAW data. The X-Trans sensor doesn't use the same regularly-repeating distribution of red, green, and blue pixels as every other Bayer-sensor array, so the process of summing the pixel mosaic is more complex.

Your explanation--that the difference between RAW data and a raster image is only physical dimension--makes no sense at all. It's not even true for the Sigma-Foveon sensor design, which does actually collect all color information in each camera sensor pixel. In that case, the the RAW file contains three times the "pixel" count of the eventual raster file--two color channels and one color-luminance channel.

Basically, Dave Stott is 100% correct.

When you make changes in Lightroom (and ACR), you're altering the Bayer interpolation process for your RAW data. Lightroom (and ACR) give you a preview that show you how your interpolated data will look based on the changes you've requested. But you aren't altering raster pixels because none have been produced--except, of course, for those of the preview image. Lightroom and ACR only produce a raster image when you leave them--when you export to a TIFF or a JPEG in Lightroom, or when you exit ACR in photoshop.

This is why Lightroom is powerful. Any change you make is simply a filed instruction on how to process RAW; you're never actually touching the RAW data itself.

The same is true with the Photoshop ACR plug-in. If you use ACR in conjunction with Photoshop Bridge, you're basically using Lightroom with a somewhat different UI.

The same is not true with Photoshop as a whole. Photoshop alters real raster pixels. That's what it does, that's why it exists. When Marvin the Martian, who's never seen any of this stuff, asks the president of Adobe, "what is this 'Photoshop' I have heard you earthlings speak of while aiming my Illudium Q-36 Explosive Space Modulator?" the president of Adobe says, "It's a raster image editor; it alters pixels."

This thread is seriously goofy, and it probably needs to stop before further bloviating confuses anyone else. It's based on this weirdo premise that Lightroom and Photoshop are competing rather than complementary products, and that your skill / talent / perspicacity as a photographer rests largely on your "choice" among them. Good grief. Good luck trying to make Marvin the Martian understand that.

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