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Making sure this is up to date.

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git-svn-id: https://svn.code.sf.net/p/gphoto/code/trunk/libgphoto2@2218 67ed7778-7388-44ab-90cf-0a291f65f57c
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Nathan Stenzel
2001-09-10 00:43:29 +00:00
parent a3fdfad1c3
commit c19eefa2a0
1 changed files with 16 additions and 8 deletions
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24
camlibs/polaroid/jpeg.txt
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@@ -4,20 +4,22 @@ Oh well, I will try to explain here anyway.
Jpeg markers in general:
------------
0xFF marker# 0x00 lenth data
0xFF marker# lenth(2 bytes) data
length is the size of the information after the 0xFF XX
Quantization tables:
-------------------
0xFF 0xDB 0x00 length data
0xFF 0xDB 0x00 length tables
Funny.....for what I have the data is all 0x01's.
I guess there is a precision number in there somewhere, but I don't know.
For what I have, both quantization tables are precision 0.
Precision 1 will not be used by us. We need precision 0.
Start of Frame 0:
----------------
0xFF 0xC0 0x00 length bits-per-pixel 0x00 height(2 bytes) width(2 bytes)
#_of_components component# v/h huh component# v/h huh component# v/h huh
#_of_components sets(1 or 3 of them)
A set would be component# v/h quantization table number.
The v/h is the vertical to horizontal compression ratio.
I forget what the "huh" is.
I misplaced some info I had on the components here.
@@ -31,15 +33,21 @@ I need to sift through my email to find what number is for what.
Huffman tables:
--------------
0xFF 0xC4 0x00 length table# data
0xFF 0xC4 0x00 length ACorDC bits(16 bytes) Huffman_values
length is the size of that huffman table (you don't count the FFCO)
Table# is 0x00, 0x01, 0x10, or 0x11
Repeat until length is exhausted (usually 4 Huffman tables):
If ACorDC>0x10 it is an AC table, otherwise, it is a DC table
The length of the Huffman_values is the sum of the previous 16 bytes
Ending piece of header (I have no clue what to call it):
-------------------------------------------------------
0xFF 0xDA 0x00 length sets
The sets are 3 bytes long.
I think the sets are supposed to correspond with the huffman tables.
0xFF 0xDA length(2 bytes) #_of_components(1 byte) sets Ss Se Ah Al
Ss and Se, I guess are each one byte.
I guess Ah and Al are one byte total.
The sets are: component#(1 byte) DC+ACtable#'s
For DC+ACtable#'s, the high nibble is DC table# and the low byte is AC table#