ascii85 | a c # implementation of an ascii85 text encoding algorithm | Graphics library
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kandi X-RAY | ascii85 Summary
a c# implementation of an ascii85 text encoding algorithm.
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QUESTION
I want to encode a string in Go using ASCII encoding like my C# function below:
...ANSWER
Answered 2021-Oct-08 at 14:32ascii85.MaxEncodedLen()
returns the maximum number of output bytes for the given number of input bytes. You may use this upper estimation.
The actual number of bytes used / written is returned ascii85.Encode()
. If you passed a bigger slice to Encode()
, you must use this to slice the destination slice, bytes beyond this are "garbage".
Same goes for ascii85.Decode()
: it returns the number of written bytes, you must use that to slice the destination if you passed a bigger slice.
Also since decoding may fail (invalid input), you should also check the returned error.
Also since it's not guaranteed the given input will result in an output that is a multiple of the used 32-bit blocks, pass flush=true
to consume the given input slice (and not wait for more input).
The final, corrected code:
QUESTION
Given a random integer, for example, 19357982357627685397198. How can I compress these numbers into a string of text that has fewer characters?
The string of text must only contain numbers or alphabetical characters, both uppercase and lowercase.
I've tried Base64 and Huffman-coding that claim to compress, but none of them makes the string shorter when writing on a keyboard.
I also tried to make some kind of algorithm that tries to divide the integer by the numbers "2,3,...,10" and check if the last number in the result is the number it was divided by (looks for 0 in case of division by 10). So, when decrypting, you would just multiply the number by the last number in the integer. But that does not work because in some cases you can't divide by anything and the number would stay the same, and when it would be decrypted, it would just multiply it into a larger number than you started with.
I also tried to divide the integer into blocks of 2 numbers starting from left and giving a letter to them (a=1, b=2, o=15), and when it would get to z it would just roll back to a. This did not work because when it was decrypted, it would not know how many times the number rolled over z and therefore be a much smaller number than in the start.
I also tried some other common encryption strategies. For example Base32, Ascii85, Bifid Cipher, Baudot Code, and some others I can not remember.
It seems like an unsolvable problem. But because it starts with an integer, each number can contain 10 different combinations. While in the alphabet, letters can contain 26 different combinations. This makes it so that you can store more data in 5 alphabetical letters, than in a 5 digit integer. So it is possible to store more data in a string of characters than in an integer in mathematical means, but I just can't find anyone who has ever done it.
...ANSWER
Answered 2021-Jun-01 at 21:47You switch from base 10 to eg. base 62 by repeatedly dividing by 62 and record the remainders from each step like this:
QUESTION
Is there a "base64.b85decode" function in nodejs?
It uses the following character set -
ANSWER
Answered 2020-Feb-21 at 17:25I solved it by using the ascii85 package and using a customized character set -
QUESTION
I have used the following code to decode text stream in pdf. There are instances where the stream needs to be decoded by 2 filters. << /Length 2348 /Filter [ /ASCII85Decode /FlateDecode ] >> I decode the stream first by ASCII85Decode and then Flatedecode. For some cases, flatedecoded final result becomes null. Any idea on the issue?
...ANSWER
Answered 2020-Jan-29 at 14:46I don't know your InflaterInputStream
, so I used the System.IO.Compression.DeflateStream
instead.
I took all stream contents with /Filter [ /ASCII85Decode /FlateDecode ]
from your example file and tried to decode them in a String rawStreamChars
like this:
QUESTION
I'm trying to figure out how to swap an image that is embedded in an .eps file with a jpeg. My "template" .eps file contains several sections that look this, each representing a different image:
...ANSWER
Answered 2020-Jan-08 at 08:38Realistically you shouldn't try to replace the image.
PostScript is a programming language and unless all the EPS files you ever plan to handle are produced by the same application, and to be realistic exactly the same version of that application, then the exact semantics of the program may vary. If the semantics vary then search and replace will fail.
The section you have supplied is incomplete, it looks like its a 4 colour image in CMYK space (because it has 4 procedures to read the data, and what's probably a Decode array has 8 elements) but there is no attempt to set the colour space, nor do you know the CTM in force. Scaling a different image to fit into the same area would be difficult unless it has the same number of rows and columns.
The image data is not simply ASCII85 encoded, it is also run-length encoded (ascii85 applied after run-length encoding), and the data is supplied as interleaved rasters. A line of Cyan followed by a line of Magenta, followed by a line of Yellow and a line of blacK. In order for an image application to read this you will have to read a set of 4 rasters, undo the ascii85 encoding, and then undo the run-length encoding, then take samples individually from each raster and interleave them to produce 4 lines of CMYKCMYKCMYK... data. (Note that very few image applications can handle CMYK data at all).
In order to replace the image data, and assuming the replacement is precisely the same dimensions, you would need to decode the image data into image samples (i.e. undo the JPEG compression). Break it up into C, M, Y, K planes, run length encode the planes, then ascii85 encode each raster, then write the image data a raster line at a time.
If there are any differences in the colour space, dimensions, bits per component or encoding then you would also need to replace the section of program which reads the image data and massages it into a form suitable for passing to the interpreter, and that's going to be a large task requiring you to learn the PostScript programming language.
The 'img' procedure (which will be defined earlier in the program) takes the dictionary data and either turns it into an image dictionary to be supplied to the PostScript image operator or turns it into equivalent level 1 operands to be supplied to the image operator if the interpreter is extremely old and only supports level 1.
In general, the only way to handle EPS files is to use a full PostScript interpreter, such as Ghostscript (as used by ImageMagick and, I presume GraphicsMagick). Because you really need to interpret the program. You can make limited changes to programs which conform to the EPS specification, but wholesale replacement of image data is not one of the intended purposes.
I don't know what you mean by 'layers'. There is no concept of layers in PostScript, which is because it's a page description language; there is no need for a 'layer'. Perhaps if you could explain what you want to achieve it might be possible to offer a different solution.
[additional]
OK so the 'normal' way to proceed in this sort of situation is for the PostScript with the 'template' to be generated such that it includes the content from your customers.
Ordinarily the customer content would be supplied as EPS (might be PDF these days), the tool to create the output for the printer would generate PostScript (not EPS, a full PostScript program) and would embed the EPS in the program. That's the point of EPS, you include it in a PostScript program.
EPS files are not really editable and not intended to be altered, in fact altering them potentially invalidates the BoundingBox information. The only way to understand what the PostScript program does is to interpret it, which is why trying to search and replace is not really a future-proof solution.
I'm also a little concerned that you seem to be using JPEG compressed images in a print environment! JPEG is (ordinarily) a lossy compression method, so a JPEG compressed image will have artefacts, I'd ordinarily consider it unsuitable for the kind of process you seem to be implying here.
Now I can see several ways to approach the problem which don't involve editing the EPS file. Assuming you know the size and position of each of the 'boxes' in the EPS, and your customer content is in EPS format, you simply concatenate the files together, generating positional information as required.
PostScript has an opaque imaging model, that means that if you start with the 'template' and then set up the CTM correctly, you can include an entire EPS file in such a way that when rendered it exactly covers the area you want to replace.
To do this you need to know the precise size and location which the EPS should cover (I'm assuming you know this) and the exact area covered by the EPS, you get that from the %%BoundingBox comment of the EPS file. Its then a trivial matter to add scale and translate operations so that the EPS is correctly sized an positioned.
Here's a skeleton of what I mean:
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