DSC-F1 (serv.man2) - Sony Digital Camera Service Manual (repair manual). Page 40

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JPEG stands for “Joint Photographic Coding Experts Group”. It is an international standard for the still picture data

compression format. Originally it was the name of the group performing the standardization of natural images, but today it is
used as the name of the still picture compression format.

Currently, JPEG is used for color faxes, electronic still cameras, and multi media PCs.

In data compression, the file size is compressed based on DCT (Discrete Cosine Transform). The JPEG is able to compress

still picture data to up to 1/100 but images are considerably poor in quality. For this reason, the normal compression rate is
about 1/10 to 1/30.

With the DSC-F1, data is compressed to about 1/3.5 in the fine mode, 1/7 in the standard mode, and 1/14 in the snap shot

mode.

With the JPEG method, compression is performed for every 64 pixels (8x8) of the screen, and data before compression

(approx. 450 kbytes=3.6 Mbits) is compressed.

The image memory (32 Mbits) storing DSC-F1 images records data such as adjustment values, etc.

Fine mode

: 120 kbyte = 0.9 Mbit

n Max. 30 images

Standard mode

: 64 kbyte = 0.5 Mbit

n Max. 58 images

Snap short mode

: 32 kbyte = 0.3 Mbit

n Max. 108 images

The data amount of one image compressed by JPEG differs according to the image. (E.g. Blue only image have little data

amount.)

However, because the area for recording one image is fixed in the memory, the total number of storable images is the same.

The filing format of image data exposed by the DSC-F1 conforms to the picture MD format. For example, the data

compression rate used by the fine/standard/snap shot modes can be used also by the picture MD.

The main functions of the picture MD are as follows.

• Index image
• Protect setting
• Exposure date and time
• Rotation of image

• Album
• Comment

• Index image

When image data is input by the picture MD format, “full image data” and “index image data” are created and recorded.
Index images are small images used for image search, and can be transferred more quickly than full images due to the

smaller data amount.

When data is transferred to the PC, index images are used for displaying album and pictures in a list.

• Protect setting

Protect can be set by image to prevent accidentally erasure of images.
The protect information is sent together with the image data during data transfer.
Therefore, when protected image data is transferred to the PC, the data read by the PC is also protected.
Unless the protect is canceled, images cannot be erased with the PC software.
However images can be erased with the delete. command of the PC as one file.