I need to convert PNG to JPEG,JPEG 2000 using ImageMagick and Matlab. I want to compress all data with ratio ( e.g. 10) and then specify some file size? Any idea or solution to achieve the specific file size? How can I do it? Thanks
Imagemagick can create a JPG of your desired file size. See http://www.imagemagick.org/Usage/formats/#jpg
-define jpeg:extent={size}
As of IM v6.5.8-2 you can specify a maximum output filesize for the JPEG image. The size is specified with a suffix. For example "400kb".
Related
I'd like to batch convert .heic images (e.g. iPhone photograph) to .jpg files with imagemagick, with the goal of retaining as much of the quality from the original image as possible. To be clear, the resulting output size is not a concern.
I've been using
magick input.heic -quality 100% output.jpg
Is it possible to do better?
No, its not possible to do better per ImageMagick's website:
Set the quality to 100 to produce lossless HEIC images. Requires the libheif delegate library.
I interpret lossless as NOTHING is lost from original picture. However since you ARE converting to another file type maybe its possible you lose something, are you seeing any artifacts/issues?
I have to process a lot of images and save results to image files with transparency in Matlab. But PNG compression takes too much time for me. How can I save PNG with no compression or TIFF with transparency? Are there other ways to save an image without compression and with transparency?
It's my first question here, sorry for my bad English and wrong question style if there are any mistakes in question.
Using the TIFF class in Matlab you can write TIFFs with transparancy:
%# create a synthetic RGBA image
ch = checkerboard(100);
rgba = repmat(ch,[1,1,4]);
rgba(:,:,4) = rgba(:,:,4)==0;
rgba = uint8(round(rgba*255));
%# create a tiff object
tob = Tiff('test.tif','w');
%# you need to set Photometric before Compression
tob.setTag('Photometric',Tiff.Photometric.RGB)
tob.setTag('Compression',Tiff.Compression.None)
%# tell the program that channel 4 is alpha
tob.setTag('ExtraSamples',Tiff.ExtraSamples.AssociatedAlpha)
%# set additional tags (you may want to use the structure
%# version of this for convenience)
tob.setTag('ImageLength',size(ch,1));
tob.setTag('ImageWidth',size(ch,2));
tob.setTag('BitsPerSample',8);
tob.setTag('RowsPerStrip',16);
tob.setTag('PlanarConfiguration',Tiff.PlanarConfiguration.Chunky);
tob.setTag('Software','MATLAB')
tob.setTag('SamplesPerPixel',4);
%# write and close the file
tob.write(rgba)
tob.close
%# open in Photoshop - see transparency!
Matlab's imwrite does not have parameter for the PNG compression level. If it did, you could set it to zero for no compression. While for TIFF it does have a none option for Compression, there is no alpha channel. You can write to the old Sun Raster (RAS) format with an alpha channel and no compression. Though nothing would likely be able to read it.
"There is no uncompressed variant of PNG. It is possible to store uncompressed data by using only uncompressed deflate block"
The uncompressed deflate block uses a header of 5 bytes + up to 65535 bytes of uncompressed data per block.
http://www.w3.org/TR/PNG-Rationale.html
I have a matlab code and it generates a .png image of 1024*768 resolution. The images are about 450KB in size and I need to know how to optimise and compress these images using matlab.
Can't I play with the quality as in JPEG ?
I read the imwrite manual and don`t seem to find a good way to do this.
Is there any way to achieve it in matlab ?
By design PNG files are lossless - there is no 'quality' to be adjusted (it's probably why a mod changed your question title).
You can reduce the number of colors in the image (the color depth) which will in turn reduce filesize (PNG-8 instead of PNG-24, for example), but the whole point of PNG is it produces lossless images, so there is simple no quality value a la JPEG.
Taken from the manual :
A parameter of input in case it is JPEG:
'Quality' - A number between 0 and 100; higher numbers mean higher quality (less image degradation due to compression), but the resulting file size is larger.
imwrite(x,'c:\1.jpg','Quality',10)
edit: Sorry, I answered this one while the title was JPEG and not PNG.
PNG doesn't support any quality settings - it is a lossless format. The compression it applies is generally as good as possible.
i have to convert 60px X 60px images to png for my web site with imagemagick.
convert image.jpg image.png
But it's return an image with 4kbyte size.
I want get a size around 1kbyte.
How can i do?
thanks
Compression level is controlled by the -quality parameter, look here for more information. If you are only having images with less than 256 colors, use -format PNG8 to save some bytes. And try to add -type optimize.
Is there anyway to reduce the Image file size or Raw RGB buffer ?
Actually I have RGB buffer which it has 500KB with 320X420 size.I tried to save it to disk using UIimage and it comes to 240 KB.
As per the image size, I want it to have less than 50KB or so.(loosing quality is OK)
Is it possible ?
Thanks,
Raghu
See Trevor Harmon's excellent post on the subject.
The 240KB size sounds exactly like the raw RGB image data, uncompressed (320x420x3). Doesn't the iPhone have a PNG or JPEG exporter? The internet says to use UIImageJPEGRepresentation or UIImagePNGRepresentation and NSData writeToFile.