How do I send a base64 image to Microsoft-ocr api? - image

Question

I'm trying to use Microsoft Azure OCR API service to extract some text from an image.
The image I have for sending to the API service has a "data:image/png; base64, " structure and therefore I can't send it with content-type "application/json".
I tried sending it with content-type "multipart/form-data" or "application/octet-stream", but it also fails...
// this "url" gives me the "data:data:image/png;base64, " code
var sourceImageUrl = document.getElementById("myImage").src;
// Perform the REST API call.
$.ajax({
url: uriBase + "?" + $.param(params),
// Request headers.
beforeSend: function(jqXHR){
jqXHR.setRequestHeader("Content-Type","multipart/form-data");
jqXHR.setRequestHeader("Ocp-Apim-Subscription-Key", subscriptionKey);
},
type: "POST",
// Request body.
data: [sourceImageUrl]
})
.done(function(data) {
// Show formatted JSON on webpage.
$("#responseTextArea").val(JSON.stringify(data, null, 2));
})
.fail(function(jqXHR, textStatus, errorThrown) {
// Display error message.
var errorString = (errorThrown === "") ?
"Error. " : errorThrown + " (" + jqXHR.status + "): ";
errorString += (jqXHR.responseText === "") ? "" :
(jQuery.parseJSON(jqXHR.responseText).message) ?
jQuery.parseJSON(jqXHR.responseText).message :
jQuery.parseJSON(jqXHR.responseText).error.message;
alert(errorString);
});
I am bit confused about how I should be sending the image or if I should do some transformations.
Which content-type should I be using to do a proper request?
Should I change the encoding of the image source? How?
Thank you all!

Answer 1

I finally got it working by adding a makeBlob function that returns a blob out of a base64 code. I also set the content-type to "application/octet-stream".
Final code looks like this:
function makeblob(b64Data, contentType, sliceSize) {
contentType = contentType || '';
sliceSize = sliceSize || 512;
var byteCharacters = atob(b64Data);
var byteArrays = [];
for (var offset = 0; offset < byteCharacters.length; offset += sliceSize) {
var slice = byteCharacters.slice(offset, offset + sliceSize);
var byteNumbers = new Array(slice.length);
for (var i = 0; i < slice.length; i++) {
byteNumbers[i] = slice.charCodeAt(i);
}
var byteArray = new Uint8Array(byteNumbers);
byteArrays.push(byteArray);
}
var blob = new Blob(byteArrays, { type: contentType });
return blob;
}
function recognizeText() {
imageToSend = image.src;
binDataImage = imageToSend.replace("data:image/png;base64,","");
// Perform the REST API call.
$.ajax({
url: uriBase + "?" + $.param(params),
// Request headers.
beforeSend: function(jqXHR){
jqXHR.setRequestHeader("Content-Type","application/octet-stream");
jqXHR.setRequestHeader("Ocp-Apim-Subscription-Key", subscriptionKey);
},
type: "POST",
// Request body.
data: makeblob(binDataImage, 'image/jpeg'),
cache: false,
processData: false
})
.done(function(data) {
// Show formatted JSON on webpage.
$("#responseTextArea").val(JSON.stringify(data, null, 2));
})
.fail(function(jqXHR, textStatus, errorThrown) {
// Display error message.
var errorString = (errorThrown === "") ?
"Error. " : errorThrown + " (" + jqXHR.status + "): ";
errorString += (jqXHR.responseText === "") ? "" :
(jQuery.parseJSON(jqXHR.responseText).message) ?
jQuery.parseJSON(jqXHR.responseText).message :
jQuery.parseJSON(jqXHR.responseText).error.message;
alert(errorString);
});
};