[Zz] thumbnail related knowledge

The so-called Thumbnail (thumbnail) is a thumbnail image in the same and JPEG image folders {Note: This data is a Windows system file, you can click/file option/View/select [show all files and folders], and cancel [hide protected operating system files] to view this data}
For Windows XP, in order to speed up reading and writing, XP does not read and write content in JPG, BMP, and other conventional image formats by default. It only reads the built-in preview content {thumbnail} of the image file }.

Due to the complexity of JPEG compression, In order to quickly view its thumbnails, the JPEG standard records some EXIF information in the file {Note: this concept should be somewhat impressive after playing digital }.
The image taken by a digital camera carries many camera parameters, all of which are EXIF information and thumbnails are part of it.
A thumbnail is a small JPEG image stored in the EXIF information segment.
Images that support the format of the exifinpu image data library are in addition to the format (.jpg).jpeg and. jpe), as well as PSD, PDD, EPS, Tif, Tiff, and other formats.

Windows reads "thumbs. DB "{Note: thumbnail database} determines whether a thumbnail of the image exists. {Note: When you change the XP topic, you may see that the thumbnail of the image and folder is a bit out of coordination, this is because "thumbs. DB "file not changed },
If the "thumbs. DB" file does not exist or the image thumbnail does not exist in the library,
Windows will try to obtain the EXIF information in the image to determine whether there is thumbnail data.

If there is no thumbnail or information error in the EXIF information in the image, Windows will use the extract value algorithm {actually belongs to the interpolation algorithm, I think this is the time to call the extract value algorithm} to re-generate a thumbnail and save it to "thumbs. DB "in the thumbnail database.
Most of the images downloaded from the internet have their own thumbnails, but only a few do not. All the images created using Photoshop have thumbnails.
{Note: EXIF will be erased after you perform layer and rotation operations on the photo in a version earlier than ps7.0}
{Note: Because the EXIF information is added to the JPEG file header with the relevant shooting parameters and indexes, the digital photos must first read the EXIF information, when we process the captured photo with some image processing software, the EXIF information will be lost or damaged, so sometimes, when we put the processed photos back in digital, the digital will not be able to read them one after another. This is what my Fujifilm camera does}

----------------------------------------------------
This chair image is a thumbnail modified by someone else in the EXIF information, so the thumbnail is different from the original image. This is not a bug in XP.

For reference, the exif2.1 standard contains the following information:
----------------------------------------------------
Image Description: Image Description and source. It refers to the image generation tool.
Artist author {some cameras can enter users' names}
Make producer {refers to the product manufacturer}
Model refers to the device model}
Orientation direction {some cameras support, some do not support}
Xresolution/yresolution x/y direction resolution this topic already has a special item to explain this problem.
Resolutionunit resolution unit is generally PPI
The software displays the firmware version.
Datetime Date and Time
Ycbcrpositioning color phase Positioning
Exifoffsetexif information location, defines the write of EXIF information in the file, some software does not show.
Exposuretime: shutter speed
Fnumber aperture Coefficient
Exposureprogram specifies the program-based Automatic exposure settings. Different cameras may have Suter priority (SHUTTER first), aperture priority (SHUTTER first), and so on.
ISO speed ratings sensitivity
Exifversion EXIF version
Datetimeoriginal Creation Time
Datetimedigitized digitization time
Componentsconfiguration Image Construction (Multi-finger color combination solution)
Compressedbitsperpixel (BPP) indicates the degree of compression of each pixel color bit.
Exposurebiasvalue exposure compensation.
Maxaperturevalue maximum aperture
Meteringmode: Average, central, and point.
Lightsource light source refers to white balance settings
Whether or not Flash is used.
Focallength focal length. Generally, the physical focal length of the lens is displayed. Some software can define a coefficient to display the focal length equivalent to 35mm of the camera.
Makernote (User comment) author Mark, description, record
Flashpixversionflashpix version (supported by some models)
Colorspace Color Gamut and Color Space
Exifimagewidth (pixel x dimension) Image Width refers to the number of horizontal dimensions
Exifimagelength (pixel y dimension) Image Height refers to the number of vertical dimensions
Interoperability IFD generic extended item definition pointer is related to the TIFF file, the specific meaning is unknown
Filesource source file
Compression compression ratio.

 

Lanczos Algorithm. Let's talk about it.