आप jpeg बाइनरी डेटा को एक फ़ाइल के रूप में लोड कर सकते हैं और jpeg हेडर को स्वयं पार्स कर सकते हैं। जिसे आप देख रहे हैं वह 0xFFC0 या फ़्रेम हेडर का प्रारंभ है:
Start of frame marker (FFC0)
* the first two bytes, the length, after the marker indicate the number of bytes, including the two length bytes, that this header contains
* P -- one byte: sample precision in bits (usually 8, for baseline JPEG)
* Y -- two bytes
* X -- two bytes
* Nf -- one byte: the number of components in the image
o 3 for color baseline JPEG images
o 1 for grayscale baseline JPEG images
* Nf times:
o Component ID -- one byte
o H and V sampling factors -- one byte: H is first four bits and V is second four bits
o Quantization table number-- one byte
The H and V sampling factors dictate the final size of the component they are associated with. For instance, the color space defaults to YCbCr and the H and V sampling factors for each component, Y, Cb, and Cr, default to 2, 1, and 1, respectively (2 for both H and V of the Y component, etc.) in the Jpeg-6a library by the Independent Jpeg Group. While this does mean that the Y component will be twice the size of the other two components--giving it a higher resolution, the lower resolution components are quartered in size during compression in order to achieve this difference. Thus, the Cb and Cr components must be quadrupled in size during decompression.
हेडर के बारे में अधिक जानकारी के लिए विकिपीडिया की jpeg प्रविष्टि देखें या मुझे यहाँ उपरोक्त जानकारी मिली ।
मैंने नीचे दिए गए कोड के समान एक विधि का उपयोग किया, जो मुझे इस पोस्ट से सूर्य मंचों पर मिला :
import java.awt.Dimension;
import java.io.*;
public class JPEGDim {
public static Dimension getJPEGDimension(File f) throws IOException {
FileInputStream fis = new FileInputStream(f);
// check for SOI marker
if (fis.read() != 255 || fis.read() != 216)
throw new RuntimeException("SOI (Start Of Image) marker 0xff 0xd8 missing");
Dimension d = null;
while (fis.read() == 255) {
int marker = fis.read();
int len = fis.read() << 8 | fis.read();
if (marker == 192) {
fis.skip(1);
int height = fis.read() << 8 | fis.read();
int width = fis.read() << 8 | fis.read();
d = new Dimension(width, height);
break;
}
fis.skip(len - 2);
}
fis.close();
return d;
}
public static void main(String[] args) throws IOException {
System.out.println(getJPEGDimension(new File(args[0])));
}
}
jstack
)।