22 Replies Latest reply on May 16, 2011 8:08 PM by Andrew_Hart

    A very basic question

    ct44

      Something has been bothering me for a while now.  I have used ACR for several years but have never discovered what I am looking at when I open an image in ACR.   I understand that the RAW image is the unprocessed image with settings that can be applied - from what I understand it is metadata that can change the parameters of the image and nothing is actually altered except these metadata instructions.   SO - what are we looking at when we view an image in ACR.  I don't see a bunch of zeros and ones - I see an image - so it must be an interpretation of the metadata.    So what gives us the image?  Is it a jpg preview or what?  Something has been done to enable us to view the RAW data.   Can someone please enlighten me after all these years.

       

      Many thanks

        • 1. Re: A very basic question
          Yammer Level 4

          You guessed right. It's an accurate preview of how the converted image will look, given the current workspace and develop settings.

          • 2. Re: A very basic question
            rjbuck

            The NEF has an imbedded JPEG image.  You are seeing a preview based on that JPEG and any in camera setting you made i.e. sharpening etc.

             

            Message was edited by: rjbuck

            • 3. Re: A very basic question
              Yammer Level 4

              Not in ACR you're not.

              • 4. Re: A very basic question
                Vit Novak Level 3

                Raw image consist of data from sensor and some additional data in form of exif tags. Obviously, data form sensor = image itself, as captured by sensor. Additional data are mostly descriptive and don't affect the result in ACR (date, exposure, aperture ... ) but some of them are used by ACR, like camera model, white balance info etc. Jpeg preview made by the camera can also be embedded and is embedded in nef, cr2 ... files. But when opening raw file in ACR, you don't see that preview - you see interpretation of data from the sensor, transferred from sensor color space to color space of your monitor and modified by various settings in ACR (exposure, saturation, contrast, profile ...)

                • 5. Re: A very basic question
                  rjbuck Level 1

                  I realized my mistake after I posted it.  I tried to delete it or edit it, but was unable.  Sorry if I caused any confusion

                  • 6. Re: A very basic question
                    Noel Carboni Level 7

                    To get just a bit more technical, something like the following happens:

                     

                    • The raw data, which isn't organized like an image at all in most camera files, is read from the disk and interpreted into a block of pixels of your computer's RAM.

                     

                    • The various Camera Raw controls are applied to the pixels in RAM.

                     

                    • The pixels from RAM are sent to your video card for display on your monitor.

                     

                    • Whenever you change a control, some or all of the above process is repeated.

                     

                    Modern computers are so fast that they can do the above, which literally involves billions of operations, in the blink of an eye!

                     

                    This is, of course, tremendously oversimplified for clarity.

                     

                     

                    -Noel

                    • 7. Re: A very basic question
                      Yammer Level 4

                      I'm not quite sure what was wrong with my original reply to warrant so many further explanations!!

                      • 8. Re: A very basic question
                        Noel Carboni Level 7

                        You told ct44 that he guessed right about the preview, when in fact the only time he used the word "preview" was in conjunction with the term "jpg".  So he really didn't guess right at all.

                         

                        What's seen in the Camera Raw display has NOTHING to do with JPEG previews.

                         

                        -Noel

                        • 9. Re: A very basic question
                          Yammer Level 4

                          I'm surrounded by pedants!

                          • 10. Re: A very basic question
                            Noel Carboni Level 7

                            Hey, you asked. 

                             

                            Frankly, advising him that he made a correct assumption about it being a "jpg preview" was flat wrong.  I assume you just missed reading the "jpg" part.  That might have been overlooked, but then another poster took up the JPEG cause.

                             

                            -Noel

                            • 11. Re: A very basic question
                              Yammer Level 4

                              Noel Carboni wrote:

                               

                              Hey, you asked. 

                              It was supposed to look like a rhetorical question

                              • 12. Re: A very basic question
                                ct44 Level 1

                                Thanks everyone for your explanations.  I think I understand now.

                                • 13. Re: A very basic question
                                  Andrew_Hart Level 2

                                  Ok. We've got that sorted. When you look at a file actually opened in CR you are looking at the rendered image (developed to CR defaults unless edited).

                                  .

                                  But what are you looking at when you view a thumbnail which CR builds for and displays in Bridge? Once again, it is not the embedded JPG. Is it simply a thumbnail of the rendered image converted according to the CR default settings, or is it something else?

                                   

                                  And while I'm on the point, why does CR need to build Previews as well as Thumbnails? Obviously, the thumbnails are used in Bridge, but what purpose does the Preview serve?

                                  • 14. Re: A very basic question
                                    Robert Shomler Level 4

                                    But what are you looking at when you view a thumbnail which CR builds for and displays in Bridge? Once again, it is not the embedded JPG. Is it simply a thumbnail of the rendered image converted according to the CR default settings, or is it something else?

                                    The thumbnail image is rendered image using CR edits, or CR defaults if no edits have been performed on the image.

                                     

                                    And while I'm on the point, why does CR need to build Previews as well as Thumbnails? Obviously, the thumbnails are used in Bridge, but what purpose does the Preview serve?

                                     

                                    Bridge displays the thumbnail in its Content panel. Larger preview image files are for display in the Preview panel and for full screen views such as slide show and what your view by pressing the space bar when thumbnails are selected in Content.  Bridge offers options for preview generation (including not generating them), and there is a preference setting for Bridge to generate monitor-size previews at the resolution of the largest monitor, which may produce higher quality preview images.

                                    • 15. Re: A very basic question
                                      SG... Adobe Employee

                                      Hi,

                                       

                                      Here's a nice historical whitepaper written by Bruce Fraser in 2004 you might find interesting.

                                       

                                      http://www.adobe.com/digitalimag/pdfs/understanding_digitalrawcapture.pdf

                                       

                                      regards,

                                      steve

                                      • 16. Re: A very basic question
                                        Hudechrome Level 2

                                        That was my primer back then, Steve!  Appreciate the link.

                                        • 17. Re: A very basic question
                                          Andrew_Hart Level 2

                                          Thanks, Robert.

                                           

                                          If the thumbnails are rendered then obviously the previews are as well. I'd thought as much. The amazing, and extremely useful, thing, for me, about Bridge is the almost instantaneous speed at which you can resize the thumbnails on the fly.

                                           

                                          I'd forgotten about the Preview panel, rarely ever use it. Suppose I should have twigged to the use of previews by slide show and spacebar viewing, the latter of which I use constantly.

                                           

                                          Out of curiosity, where in Bridge Preferences do you find the option NOT to generate previews? I've looked and can't see it anywhere.

                                          • 18. Re: A very basic question
                                            Andrew_Hart Level 2

                                            Steve,

                                             

                                            Yes, thanks, I'd read that Fraser whitepaper many years ago. However on rereading it I confirmed my recollection that it had nothing to say about the nature of the images comprising the thumbnails and previews generated by CR for Bridge. Was there some other reason you mentioned it?

                                            • 19. Re: A very basic question
                                              Robert Shomler Level 4

                                              Out of curiosity, where in Bridge Preferences do you find the option NOT to generate previews? I've looked and can't see it anywhere

                                              It is not in preferences; option to not generate previews may be selected by buttons in the Bridge application bar.  Mouse over the first button and you should see "Browse Quickly By Preferring Embedded Images," which will direct Bridge to use the thumbnails embedded in the source file.  You can click on that to toggle 'prefer embedded' on and off.  Or mouse over the next button, which should display "Options For Thumbnail Quality And Preview Generation."  Click on that for pulldown menu then you can select "Prefer Embedded (Faster)" to accomplish  the same as the toggle button.  That pulldown also includes an option "High Quality On Demand" -- use embedded thumbnail and delay rendering preview until needed -- when you preview an image.

                                               

                                              The option to generate monitor-size previews is in Preferences.

                                              • 20. Re: A very basic question
                                                Andrew_Hart Level 2

                                                Ah, I see, thanks.

                                                 

                                                Not much point to choosing "preferring embedded images" for either thumbnails or previews because the embedded JPEGs of proprietary Raw files, as distinct from DNGs, can't be updated with the ACR edits. Also, you can't mix and match, ie you either have to settle with one or the other, namely embedded JPEGs for both thumbnails And previews, or ACR generated thumbnails And previews derived from the rendered files. Only the latter is really satisfactory, IMO.

                                                • 21. Re: A very basic question
                                                  ELPDave@gmail.com

                                                  Hi,

                                                   

                                                  I read  your question and, probably, you've already pretty much had the question answered

                                                  in your mind. Like you, I wondered about the question, and I bought a great book from

                                                  Amazon called "Camera Raw with Adobe Photoshop CS5"

                                                   

                                                  This book has really revolutionized how I have started to use Adobe. I probably don't have the time

                                                  you have on this program - I'm about a year and a portion in use - but this book is really great

                                                  at explaining how we look at colors and how our camers look at colors.

                                                   

                                                  This book has taught me so much  on how to use Camera Raw!!

                                                   

                                                  "Camera Raw with Adobe Photoshop CS5

                                                  by Jeff Schewe and Bruce Fraser"

                                                   

                                                  Real World Books -  I bought mine on Amazon

                                                   

                                                  Thanks

                                                   

                                                  Dave Harman

                                                  • 22. Re: A very basic question
                                                    Andrew_Hart Level 2

                                                    Dave,

                                                     

                                                    Thanks, I also have a copy of Schewe's book. If it touches upon the nature of the images comprising the Previews in Bridge I hadn't noticed it. But as you say, its all academic now that we have it sorted out.