But the application reduces this 32-bit file to 8-bits when we see it on our screen. When working with multiple images of the same scene exposed at different levels to create an "HDR" image we often use applications that create a 32-bit floating point file. In most editing environments the image on your screen is an 8-bit image very similar to a jpeg image, but the demosaiced data used to create that image may have higher bit rates. What is changed is the way your editing application interprets and displays a portion of the information from that data. When you move the sliders or change the numerical values for various settings the raw data is not changed. It is a preview image generated by the raw editing application you are using by applying your current settings to the raw data that results in the image you view on the LCD. The image you see on your computer screen when you are editing a raw file is not the raw data. The gamma correction and any additional shaping of the light response curves is what sets brightness and contrast. How much bias is given to red, green, and blue in the demosaicing process is what sets white/color balance. This is the process we refer to as demosaicing. When the tonal values (gray intensities) of adjoining pixels filtered for the three different colors used in the Bayer mask are compared then colors may be interpolated from that information. What it does is change the tonal value (how bright or how dark the luminance value of a particular color is recorded) of various colors by differing amounts. But just like putting a red filter in front of the lens when shooting black and white film didn't result in a monochromatic red photo, the Bayer mask in front of monochromatic pixels doesn't create color either. Color is derived by comparing adjoining pixels that are filtered for one of three colors with a Bayer mask. As such there is no color information to a raw file. It is a set of single luminance values for each pixel on the sensor. (My background - I've used Photoshop since version 2.5, but I've only recently purchased Lightroom)įirst, let's remind ourselves of what a raw file is. With this non-destructive editing, the original information is preserved and edits can be tweaked or removed in the future. The difference between Photoshop and Lightroom (and one of the reasons Lightroom exists as a separate product), is that edits aren't applied as pixels to a raster image, but are saved as instructions for Lightroom on how to display the RAW file. Once Photoshop has opened the image and edited it, there are a number of file formats that you can use to save the image, some of which are capable of keeping the image as 16-bit and maintaining Photoshop layers, etc., but - as far as I understand - there isn't a way to deconstruct a Photoshop edited image back to a RAW file that has the same type of information stored the same way as a regular RAW file. Photoshop is a general purpose raster image editor, and as you state it requires an intermediate step in order to open a RAW file (which is not, as such, an RGB raster image format).
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