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FAQ / FILE MANAGER > COMPRESS IMAGES
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Compress BMP JPEG PNG TIFF graphic files



COMPRESSION OF IMAGE FILE TYPES

OPTIMIZE PICTURE DISK SPACE OCCUPATION (FORMAT, SIZE)

MORE INFORMATION ABOUT GRAPIC DATA COMPRESSION

optimize picture compression



Some types of graphic files (as lossy or lossless .JPEG, .PNG, .GIF, and compressed .TIFF) may be difficut to be efficiently compressed, as some picture/photo file formats employ specific algorithms meant to efficiently compress graphic data, and consequently the already compressed image formats leads to very poor compression ratio when added to an archive using general purpose compression algorithms, even if higest compression levels are set.

When archiving already compressed graphic files it is recommended to use lowest/fastest compression settings in order to spare compuational resources, rather than gaining a small percentual improvement of compression using maximum compression sets or slower algorithms, as the tradeoff between performance penaly and compression ratio gain would not be favourable - if it is needed to keep output under a maximum size limit (i.e. for email attachment), it may be recommended, instead, to split output in multiple volumes.

Alternative ways, detailed below, to reduce images disk occupation are to conver picture format to a more suitable one (this apply graphic-specific compression on the data), or to reduce actual image size, either by cropping (reduce the picture to a smaller selection, containing relevant images) or resizing it to a smaller size suited to the intended use.

Optimize picture disk space occupation (format, size)


How to convert picture format


An alternative approach to enhance compression efficiency of pictures, photo and CGI graphic files is chosing the most appropriate graphic coding format, and convert original picture to a more suitable image format.

optimize images for the web

In example, PNG (and to a lessen extent compressed TIFF) is extremely efficient on regular shapes with low noise (geometric shapes, charts, simple drawings and computer-generated imagery imagery) so recompressing a raw BMP or uncompressed TIFF file to PNG format can really improve disk occupation - moreover, being PNG compression lossless, no actual picture's data is lost in the transformation.

On the other side, JPEG is more efficient on photographic images, even with average or high noise, so it should be chose over BMP, compressed or uncompressed TIFF, and PNG when saving actual photo or scans rather than CGI graphic; it is consequently a popular choice for consumer / prosumer digital photograpy.

Lossy JPEG compression, however, degrades the quality of the picture data at each iteration, so for better results it is recommended to keep original data, edit it using lossless formats (PNG, TIFF, or specific photoediting file formats) for intermediate steps, and only apply lossy JPEG compression when finalizing the work - keeping in account the platform the graphic is meant to be used for.

Uncompressed graphic files formats (i.e. RAW images, BMP files, uncompressed TIFF) usually compresses well with traditional general purpose compression (ZIP, 7Z...), but in this case is often preferable to evaluate if it is needed to keep the original, large, uncompressed files, or rather convert them to a lossless picture format (usually PNG or TIFF) that does not modify the original file information but stores it in a smaller file, ready to use/view without requiring extraction.

PeaZip features a simple set of image editing tools, with Transform dialog providing the needed functions to convert any readable picture format to BMP, PNG, or JPEG.
If JPEG format is chosen, lossy JPG compression quality can be set in a range from 0 to 100: lower quality means more efficient picture compression and smaller output pictures, but the increase of JPG compression artifacts will degrade the quality of the image; higher JPG quality value will result in better pictures, but saved to larger output files.

How to crop and resize images


Another critical factor for optimizing graphic files disk occupation is picture size, i.e. reducing the original picture size to 50% brings the output to the 25% of the original file size.

Resizing the picture to a smaller size (featured in PeaZip graphic files' Transform dialog) is a lossy operation: the removed information is lost and expanding back the image to a larger size will not add back the original information, so resizing the graphic should be done in the final step, accurately chosen for the intended platform.
If the smaller size is acceptable for the intended use, reducing picture size is a very effective mean to decrease file size.
PeaZip's Transform dropdown menu also features fit to screen pre-sets entries to scale the image to most common screen sizes.

Picture cropping (provided by PeaZip picture Crop dialog), removes unwanted or less important area of the raw image: it is too an obviously lossy operation and cut area cannot be recovered from the cropped image, but in this way both size of the picture and size of the file can be reduced without altering the quality of the remaining portion of the graphic.

More information about graphic data compression


External online resources: computer generated imagery (CGI)reduce file size without loss wiki, digital photographyreduce file size without loss wiki, RAW image formatreduce file size without loss wiki, lossyjpeg compression and losslessreduce file size without loss wiki compression definition on Wikipedia.

Topics and serach suggestions: crop, resize, compress pictures wiki, fit to screen, convert graphic files, optimize and re-compress images, reduce disk occupation of pictures collections, improve JPEG, PNG, TIFF, GIF, BMP, raw files compression, photo scaling and cropping for the web.


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