Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>If you're OK with region co-ordinates being multiples of 8, the JPEG library from <a href="http://www.ijg.org/" rel="nofollow noreferrer">ijg</a> may be able to help you load partial JPEG images.</p> <p>You'd want to:</p> <ol> <li>Get all DCT coefficients for the entire image. Here's an <a href="https://stackoverflow.com/questions/4470107/extracting-dct-coefficients-from-encoded-images-and-video">example of how to do this</a>. Yes, this will involve entropy decoding of the entire image, but this is the less expensive step of JPEG decoding (IDCT is the most expensive one, and we're avoiding it).</li> <li>Throw away the blocks that you don't need (each block consists of 8x8) coefficients. You'll have to do this by hand, but since the layout is quite simple (the blocks are in scanline order) it shouldn't be that hard.</li> <li>Apply block inverse DCT to each of the frames. You can probably get IJG to do that for you. If you can't, then you'll have to do your own IDCT and color transform back to [0, 255] because intensities are in [-127, 128] in the world of JPEG.</li> <li>If all goes well, you'll get your decoded JPEG image. Because of <a href="http://en.wikipedia.org/wiki/Chroma_subsampling" rel="nofollow noreferrer">chroma subsampling</a>, the luma and chroma channels may be of different dimensions, and you will have to compensate for this yourself by scaling.</li> </ol> <p>The first two steps are pretty much covered by the links. The fourth one is quite trivial (you can get the type of chroma subsampling using the IJG interface, and scaling -- essentially upsampling -- is easily achieved by using something like <a href="http://opencv.willowgarage.com/wiki/" rel="nofollow noreferrer">OpenCV</a> or rolling your own code). The <strong>third</strong> one is something I haven't tried yet, but it sounds like it would be possible.</p>
    singulars
    1. This table or related slice is empty.
    1. POLarge JPEG/PNG Image Sequence Looping
      singulars
      1. PTQuestion
    1. PTAnswer
    1. USCommunity
    1. USmisha
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    1. CO+1: But you might want to add the rescaling of the different color components and the color transform.
      singulars
      1. PO
      1. This table or related slice is empty.
    2. COThanks for pointing that out. I updated the answer. BTW, IJG does the color transform as part of its IDCT step so you only have to do that yourself if you're using a different library for the IDCT.
      singulars
      1. PO
      1. USmisha
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload