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Understanding the effects of compression

From: Scanning Techniques for Photography, Art, and Design

Video: Understanding the effects of compression

Previously we discussed the evils of applying interpolation to your image and the benefits of minimizing the amount of interpolation. Here I would like to visit a similar related topic and that is Compression, and where we want to avoid it and particularly if you're trying to maintain maximum image quality. What we have on screen here is two images. The one on the left is saved out as a . PSD, a native Photoshop file coming right from a RAW file, no compression. On the right is another version of this file. It's saved out instead of .PSD as a level 4 JPEG, so fair amount of JPEG compression has been applied to.

Understanding the effects of compression

Previously we discussed the evils of applying interpolation to your image and the benefits of minimizing the amount of interpolation. Here I would like to visit a similar related topic and that is Compression, and where we want to avoid it and particularly if you're trying to maintain maximum image quality. What we have on screen here is two images. The one on the left is saved out as a . PSD, a native Photoshop file coming right from a RAW file, no compression. On the right is another version of this file. It's saved out instead of .PSD as a level 4 JPEG, so fair amount of JPEG compression has been applied to.

When you look at these two images, as you can see here we're looking at them at 100%, the image quality is fairly similar although the more you look in some of the details here you can see that this doesn't have quite as much detail. But you know what at a cursory inspection both images look okay. So you know maybe saving it out as JPEG is not so bad. But now let's zoom in and let's take both images up so we're comparing exactly the same view to 250%. We'll take the one on the right to 250 as well, and let's orient them just about the same on the screen and now look at there detail.

Couple of different places here, take a look at down in this area where you have the big indent in through here and compare the same area, see how broken up. You can see these blocks of pixels that are created by the JPEG compression. What's going on here is that this is a lossy type of compression which means that data in the image is averaged and then re-created so you end up with losing a lot of sharpness and a lot of detail in your image. And look along this one vein here and up in this area where you see lots of fine detail, all of that detail is completely lost up in here because of the JPEG compression. Now if you're viewing this on screen at 100%, in particularly even smaller, not a big deal, if you're printing to a low-quality printing device doesn't show up nearly as much.

But when you're printing to high-quality devices that really do show the detail, such as a very high-quality inkjet printer or a commercial printing press you're really going to see the differences in image quality, sharpness, and detail. In addition to avoiding interpolation we want to avoid compression as much as possible if you want to maintain maximum image quality.

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This video is part of

Image for Scanning Techniques for Photography, Art, and Design
Scanning Techniques for Photography, Art, and Design

58 video lessons · 8474 viewers

Taz Tally
Author

 
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  1. 6m 48s
    1. Welcome
      1m 11s
    2. What you should know before watching this course
      3m 54s
    3. Using the exercise files
      1m 43s
  2. 1h 0m
    1. Scanners and digital cameras
      3m 6s
    2. Types of scanners
      5m 2s
    3. Scanner location
      3m 19s
    4. What scanners and digital cameras create
      7m 22s
    5. Understanding grayscale values and channels
      3m 19s
    6. Understanding pixels and vectors
      4m 1s
    7. Choosing pixels or vectors
      2m 27s
    8. Resolving resolution
      6m 32s
    9. Working with interpolation
      3m 31s
    10. Understanding the effects of compression
      2m 4s
    11. Evaluating and correcting images with histograms
      8m 26s
    12. Saving to different file formats
      7m 4s
    13. Color management
      4m 23s
  3. 33m 22s
    1. Cleaning your scanner
      7m 31s
    2. Cleaning your images
      7m 47s
    3. Calibrating your scanner
      9m 13s
    4. Creating and applying a color management profile
      8m 51s
  4. 20m 55s
    1. Evaluating your scan challenges
      9m 46s
    2. Reproducing vs. assigning colors
      6m 20s
    3. Recognizing continuous tone (contone) vs. dot pattern images
      4m 49s
  5. 36m 32s
    1. Understanding bit depth
      8m 49s
    2. Selecting a scan mode
      8m 20s
    3. Sharpening and its effects
      10m 40s
    4. Creating and assigning color management profiles
      8m 43s
  6. 2h 25m
    1. Taking the Tazmanian Oath!
      3m 38s
    2. Choosing your weapon
      4m 2s
    3. Setting up your scanning preferences
      12m 14s
    4. Performing a prescan
      2m 53s
    5. Assigning a scan frame
      5m 40s
    6. Determining scan resolution
      7m 57s
    7. Choosing a scan mode and bit depth
      5m 53s
    8. Naming images
      1m 49s
    9. Scanning simple logos and line art
      12m 21s
    10. Scanning complex line art
      7m 33s
    11. Scanning grayscale contones
      13m 22s
    12. Scanning color contones
      13m 54s
    13. Sharpening
      9m 39s
    14. Scanning printed/screened or patterned images
      7m 1s
    15. Scanning positive transparency film
      12m 33s
    16. Scanning negative transparency film
      9m 11s
    17. Capturing high dynamic range (HDR) scans
      1m 47s
    18. Setting up wet scans
      14m 29s
  7. 1h 48m
    1. Scanning, converting, and using simple line art
      5m 32s
    2. Scanning and using detailed line art
      10m 52s
    3. Scanning landscapes
      15m 50s
    4. Scanning product shots
      11m 58s
    5. Scanning combo/complex images
      9m 3s
    6. Adjusting distressed images
      11m 12s
    7. Scanning images with no neutrals
      11m 57s
    8. Post-scan touch-ups
      2m 7s
    9. Scanning images for multiple uses
      10m 44s
    10. Automatic scanning
      10m 40s
    11. Streamlining big jobs with batch scanning
      5m 22s
    12. Using your manufacturer's scanning software
      3m 14s
  8. 27s
    1. Goodbye
      27s

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