I've read lossless jpeg is invoked when the user selects a 100% quality factor in an image tool.
What is the image tool they meant?
Thanks in advance.
OK Image Compression is sorta like a ZIP file; JPG Takes up less space but has less quality then a PNG or TIFF. In short it removes Bytes and Changes The Algorithm, the Higher the Quality The More Space it Takes for the Algorithm Compression, Read More Here:
https://en.wikipedia.org/wiki/Lossless_compression
Related
I'm converting images with embedded ICC profiles to the sRGB color space using LittleCMS. I want to efficiently detect when this conversion is lossy due to the image containing pixels that are out-of-gamut for the sRGB (e.g. the image is using Display P3 and contains saturated colors).
Note that I don't want to merely check if the embedded profile has a wide gamut, because the image pixels may not be taking advantage of its full gamut, and still fit in sRGB.
I know there's cmsSetAlarmCodes, but this seems like it could cause false positives, because there's nothing stopping the image from actually containing the same color that I set for my alarm color. Does LCMS have some out of band signal for this?
Another approach that comes to my mind is applying conversion twice: to sRGB and then back to the original color space, and checking how lossy it was. But that more than doubles processing time. Is there a more efficient way?
I've successfully used jpegtran to combine JPEGs of the same size (512x512) using the method described in this stackoverflow answer: https://stackoverflow.com/a/29615714/2364680
These are tiled JPEGs from the internet that make a 360 panorama when combined. As I said, the 512x512 images combined perfectly with jpegtran; however, I realized that some of the tiles that make up the panorama are 256x256 and need to be doubled in size when combined with the other tiles in order to form the panorama (in the 2D form of an equirectangular projection).
Simply put, I need to know if jpegtran can losslessly combine two JPEGs of different sizes -- for instance, if I can losslessly double the resolution of a 256x256 tile and then combine it with another 512x512 tile.
I know this can be done through reencoding, but I'm asking if it can be done totally losslessly. Thanks.
Not currently, no. We'd need the following:
Lossless crop - long supported
SmartScale - note that this is not ITU JPEG compliant, will change the pixel size of macroblocks, and will fail with many decoders.
Ability to change macroblock size partway through a file. My guess is that SmartScale doesn't support this, but some newer image/video compression formats do.
Supporting software - not currently available. I tested the latest available at this time, JPEG-9e, which cannot append JPEGs of differing SmartScale ratios / macroblock sizes
Here's what I came up with given that jpegtran's -crop, -scale and -drop operations cannot be combined:
#start with two images
#512x512.jpg - 64x64 macroblocks
#256x256.jpg - 32x32 macroblocks
#uncrop 2x1x using libjpeg7+ to give us space for later.
#out.jpg resolution is 1024x512, 128x64 macroblocks
jpegtran -crop 1024x512+0+0 -outfile out.jpg 512x512.jpg
#upscale the 256px image to 512x512 using libjpeg8+'s SmartScale
#Note: Does not change image width/height in macroblocks!
#Note: Only changes width/height of macroblocks!
#upscale.jpg is 512x512 but still 32x32 macroblocks
jpegtran -scale 8/4 -outfile upscale.jpg 256x256.jpg
#drop in upscale.jpg on the right half of the output image.
jpegtran -drop +512+0 upscale.jpg -outfile out.jpg out.jpg
However, the last command fails with: "Bogus virtual array access" which is the string for JERR_BAD_VIRTUAL_ACCESS error thrown by jpeg-9e/jmemmgr.c line 857.
It fails because end_row > ptr->rows_in_array where rows_in_array is 32 macroblocks and end_row reaches 33 macroblocks - the first macroblock row not present in upscale.jpg
jpegtran is expecting a 512x512 pixel image to be 64x64 macroblocks using the destination image macroblock size, so halfway through upscale.jpg it runs out of source macroblocks and walks off the end of the image. If we patched libjpeg to use the correct macroblock size, we'd need some way to encode into the file that the size of macroblocks has changed, but I'm not sure how that would be done.
I am reading a jpeg image (input.jpg) and on writing the same image on disk(as output.jpg), why does its size getting changed. Can i retain the same size.
library(jpeg)
img <- readJPEG('input.jpg')
file.info('input.jpg')$size
writeJPEG(img,'output.jpg',1)
file.info('output.jpg')$size
#is different from input.jpg size
Well, what's you doing is not reading and writing back the same file. readJPEG decodes compressed (lossy) JPEG data into raster array, writeJPEG encodes it back again. To get approximately the same size, you should (at least) set quality parameter to appropriate value. See ?writeJPEG:
writeJPEG(image, target = raw(), quality = 0.7, bg = "white", color.space)
There are a number of factors that affect the compression:
Sampling Rates
Quantization table selection
Huffman tables (optimal or canned)
Progressive or Sequential
If progressive, the breakdown of the scans.
Metadata included
If you do not compress using the same settings as the input, you will get a different size.
You can also get rounding errors in the decompression process that could cause slight differences.
I have a image with size of 5760 x 3840px with size of 1.14mb. But I would like to reduce its size to 200 kb by not changing the dimensions of the image. How Could I do this using photoshop? Please help me
This answer is based on a large format file size that has a resolution of 300 dpi. If the image is 5760 x 3840, your canvas size will be 19.2 x 12.8. in order to not "reduce" the dimension (printable area) you are going o have to reduce the image size [ALT + CTRL/CMD + I] and then reduce the resolution from there.
At 300 DPI:
At 72 DPI:
This reduction in resolution can decrease the file size dramatically, There is a chance of artifacts, but as you are starting at a high resolution the compression algorithms will smooth it out to almost non-existent.
NOW... If you are starting at 72dpi and you are looking for a good way to generate a lower file size for the web, your best bet may be to do a Safe for web option [ALT + CTRL/CMD + SHIFT + S] and generat a .jpg, .gif or a .png based on the final needs of the file. If it is an photograph with a lot of colors, I would go .jpg. If you have a lot of areas of solid color (logo perhaps) I would go with .png or .gif.
The Save for Web option allows you to see, side by side, the results of the export BEFORE going through the save process. it also allows you to alter the settings of the save process to dial in your results. best of all, it gives you a pretty good preview of the expected file size.
Either way this should help you save that larger file size for future use.
I am currently doing an assigment and cannot find the answer to this question..as Algorithm is supposed to mean (solving problems as such)
The main difference is that JPEG uses a lossy algorithm, and GIF uses a losless algorithm (LZW). In addition, GIF is limited to 256 colors, while JPEG is truecolor (8 bits per color per pixel)
Some info is here.
Basically, JPEG is good for real life images, and GIF is good for computer generated images with solid areas or when you need some text to not be blurred (JPEG is lossy, GIF is not). There are many other differences too.
See also Wikipedia:
GIF
JPEG
For bonus points in your assignment you might want to mention other commonly used standards such as PNG.
i found a very good web site that explains about the difference between gif and jpeg plus it shows image examples of several scenarios. enjoy.
http://www.siriusweb.com/tutorials/gifvsjpg/