how to convert a Jpeg Base64 string to a jpeg image in Qt

Question

I am beginning with Qt

I need to convert a Base64 string of a Jpeg image into a Qimage and display it in a QLabel

Can someone please direct me as to how to go about doing this?

I think people are being a bit harsh to the OP here in marking this down. He or she is clearly new to SO and it was clear as to what they were asking, even with the unnecessary Base64 jpeg added to the question. — TheDarkKnight, Jan 08 '15 at 09:20
I am sorry for I could not make the question clear. I was trying to assign the base64 value of a jpeg picture on to a QByteArray variable. The string was more than 200,000 characters in length. The assignment was not working properly. Thanks Merlin069 for suggestions. — SAHLA, Jan 08 '15 at 10:02

Christian Rapp · Accepted Answer · 2015-01-09T19:29:16.663

5

Well there is QByteArray and QImage. QImage has loadFromData method which can be used with base64 encoded data.

QByteArray imageData = QByteArray::fromBase64("YourBase64EncodedString");
QImage img;
if (img.loadFromData(imageData)) {
    // show this label somewhere.
    QLabel label;
    label->setPixmap(QPixmap::fromImage(img)); 
}

Here you can find more information on how to read and write images

A more complete example can be found in my github repository. I wrote this app some years ago to restore base64 encoded images from e-mails that were accidentally deleted.

edited Jan 09 '15 at 19:29

answered Jan 08 '15 at 08:33

Christian Rapp

1,853
24
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Your first line of code does not have a valid syntax. Considering the OP is new to Qt, it's only going to cause confusion. – TheDarkKnight Jan 08 '15 at 09:14
You are right the syntax was not correct. I should have marked this as pseudo code. – Christian Rapp Jan 08 '15 at 09:34
Note that the OP also asks how to add the image to a QLabel. I was writing the answer when the question was closed. – TheDarkKnight Jan 08 '15 at 09:58
Ah yes missed that point :) – Christian Rapp Jan 08 '15 at 10:18
@Merlin069 Could you vote to re-open it? The question isn't that bad after you edited it. – Tay2510 Jan 08 '15 at 10:37
@Tay2510, I have already voted. – TheDarkKnight Jan 08 '15 at 10:51
Thanks @Christian Rapp for the reply. I am able to load image using this method. (But if I use toAscii() conversion there is an error) – SAHLA Jan 08 '15 at 11:17
@SAHLA No problem. I used toAscii() to convert a QString to a ByteArray. My test environment was still running under Qt4.8. With Qt 5 you have to use toLatin1(). See my edit above for a complete desktop application I once wrote. Maybe it helps... – Christian Rapp Jan 09 '15 at 19:32

score 1 · Answer 2 · answered Jan 08 '15 at 08:45

1

You can do it with QByteArray and QImage::loadFromData(const QByteArray & data)

  QByteArray barray = QByteArray::fromBase64("base64 string");
  QImage image;
  image.loadFromData(barray);

answered Jan 08 '15 at 08:45

shinichy

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1
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how to convert a Jpeg Base64 string to a jpeg image in Qt

2 Answers2